Fragmenting gadolinium: Mononuclear polyoxometalate-based magnetic coolers for ultra-low temperatures

The polyoxometalate clusters with formula [Gd(W 5O 18) 2] 9- and [Gd(P 5W 30O 110)] 12- each carry a single magnetic ion of gadolinium, which is the most widespread element among magnetic refrigerant materials. In an adiabatic demagnetization, the lowest attainable temperature is limited by the presence of magnetic interactions that bring about magnetic order below a critical temperature. We demonstrate that this limitation can be overcome by chemically engineering the molecules in such a way to effectively screen all magnetic interactions, suggesting their use as ultra-low-temperature coolers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular spintronics: the role of coordination chemistry.

Welcome to this themed issue of Dalton Transactions entitled ‘Molecular spintronics: the role of coordination chemistry’.

Carbon Nanotubes: In-Situ Growth of Ultrathin Films of NiFe-LDHs: Towards a Hierarchical Synthesis of Bamboo-Like Carbon Nanotubes (Adv. Mater. Interfaces 6/2014)

Molekulare magnetische Materialien

Spectroscopic analysis of vibronic relaxation pathways in molecular spin qubit [Ho(W5O18)2]9−: sparse spectra are key

Molecular vibrations play a key role in magnetic relaxation processes of molecular spin qubits as they couple to spin states, leading to the loss of quantum information. Direct experimental determination of vibronic coupling is crucial to understand and control the spin dynamics of these nano-objects, which represent the limit of miniaturization for quantum devices. Herein, we measure the vibrational properties of the molecular spin qubit $[$Ho(W$_5$O$_{18}$)$_2]^{9-}$ by means of magneto-infrared spectroscopy. Our results allow us to unravel the vibrational decoherence pathways in combination with $ab$ $initio$ calculations including vibronic coupling. We observe field-induced spectral cha…

Incommensurate nature of the multilayered molecular ferromagnetic metals based on bis(ethylenedithio)tetrathiafulvalene and bimetallic oxalate complexes.

The salt [ET]x[MnRh(ox)(3)].CH(2)Cl(2) (x = 2.526(1)) has been obtained and characterized. This paramagnetic metal is essentially isostructural to the ferromagnetic metal [ET]y[MnCr(ox)(3)].CH(2)Cl(2) (y approximately equal to 3) and provides a definite answer on the origin of the structural disorder present on such systems. As in the ferromagnetic analogue, this material shows high electrical conductivity at room temperature (13 S.cm(-1)) and metallic behavior.

Koexistenz mobiler und lokalisierter Elektronen in Salzen des Bis(ethylen)dithiotetrathiafulvalen-Radikals (BEDT-TTF) mit paramagnetischen Polyoxometallaten: Synthese und physikalische Eigenschaften von (BEDT-TTF)8[CoW12O40]·5.5H2O

Design of molecular materials combining magnetic, electrical and optical properties †

The possibilities offered by hybrid functional materials formed by two molecular networks in the context of crystal engineering are illustrated with two different examples: (i) hybrid magnets constructed from combination of an extended ferromagnetic or ferrimagnetic inorganic network, with a molecular paramagnetic metal complex acting as template. (ii) Hybrid organic–inorganic compounds combining an organic π-electron donor network that furnishes the pathway for electronic conductivity, with inorganic metal complexes that act as structural and/or magnetic components. These examples illustrate how this hybrid approach allows the design of molecular materials combining non-conventional magnet…

Towards Molecular Conductors with a Spin‐Crossover Phenomenon:Crystal Structures, Magnetic Properties and Mössbauer Spectra of[Fe(salten)Mepepy][M(dmit) 2 ] Complexes

Three new iron(III) compounds of formula [Fe(salten)Mepepy][M(dmit)2]·CH3CN (M = Ni, Pd, Pt; H2salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate); Mepepy = 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl) ethane; dmit2– = 1,3-dithiole-2-thione-4,5-dithiolato) have been synthesised and the crystal structure of each compound has been solved at different temperatures. The structures consist of alternating layers of [M(dmit)2]– units and [Fe(salten)Mepepy] cations. In the Ni compound photo-isomerisation of the Mepepy ligand can be observed in dichloromethane solution. The temperature dependence of the magnetic susceptibility of the compounds reveals a gradual S = 5/2 blabla S = 1/2 spin crossove…

Green Light-Emitting Solid-State Electrochemical Cell Obtained from a Homoleptic Iridium(III) Complex Containing Ionically Charged Ligands

An efficient bluish-green light-emitting Ir(III) complex was prepared by introducing charged side groups onto phenylpyridine ligands. Green light emission with a first maximum at 487 nm (CIE coordinates x = 0.337 and y = 0.501) was observed from a single layer light-emitting electrochemical cell using this new complex; this is the lowest wavelength observed so far for devices based on ionic transition metal complexes.

Polymer‐Based Composites for Engineering Organic Memristive Devices

Memristive materials are related to neuromorphic applications as they can combine information processing with memory storage in a single computational element, just as biological neurons. Many of these bioinspired materials emulate the characteristics of memory and learning processes that happen in the brain. In this work, we report the memristive properties of a two-terminal (2-T) organic device based on ionic migration mediated by an ion-transport polymer. The material possesses unique memristive properties: it is reversibly switchable, shows tens of conductive states, presents Hebbian learning demonstrated by spiking time dependent plasticity (STDP), and behaves with both short- (STM) an…

Custom coordination environments for lanthanoids: tripodal ligands achieve near-perfect octahedral coordination for two dysprosium-based molecular nanomagnets

Controlling the coordination sphere of lanthanoid complexes is a challenging critical step toward controlling their relaxation properties. Here we present the synthesis of hexacoordinated dysprosium single-molecule magnets, where tripodal ligands achieve a near-perfect octahedral coordination. We perform a complete experimental and theoretical investigation of their magnetic properties, including a full single-crystal magnetic anisotropy analysis. The combination of electrostatic and crystal-field computational tools (SIMPRE and CONDON codes) allows us to explain the static behavior of these systems in detail. NRF-2015R1A2A1A10055658 Grant NRF-2012-0008901 NRF2010-0020209 ERC-CoG-647301 DEC…

Efficient Polymer Light‐Emitting Diode Using Air‐Stable Metal Oxides as Electrodes

Poly(phenylenevinylene)‐based organic light‐emitting diodes (OLEDs) are fabricated using air‐stable metal oxides as electrodes, producing very efficient and bright electroluminescent devices. Efficiencies of 8 cd A−1 and luminances above 20000 cd m−2 are obtained, comparable to the values reported for classic OLED structures using reactive metals as cathodes.

Functionalisation of MoS2 2D layers with diarylethene molecules

Functionalisation of two dimensional (2D) materials with stimuli-responsive molecules has been scarcely investigated. Here, MoS2 layers obtained by chemical exfoliation are covalently and non-covalently functionalised using two photoswitchable diarylethene derivatives under their open- and closed-ring isomers. The choice of these light-responsive molecules is based on their excellent thermal irreversibility and fatigue resistance. The characterisation of the resultant molecular/2D heterostructures proves the successful anchoring of the molecules by both approaches as well as the influence that the driving interaction has in the photoswitching behaviour of the diarylethene isomers after thei…

Exploring the High-Temperature Frontier in Molecular Nanomagnets: From Lanthanides to Actinides.

Molecular nanomagnets based on mononuclear metal complexes, also known as single-ion magnets (SIMs), are crossing challenging boundaries in molecular magnetism. From an experimental point of view, this class of magnetic molecules has expanded from lanthanoid complexes to both d-transition metal and actinoid complexes. From a theoretical point of view, more and more improved models have been developed, and we are now able not only to calculate the electronic structure of these systems on the basis of their molecular structures but also to unveil the role of vibrations in the magnetic relaxation processes, at least for lanthanoid and d-transition metal SIMs. This knowledge has allowed us to o…

A spin-crossover complex based on a 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligand functionalized with a carboxylate group

Combining Fe(ii) with the carboxylate-functionalized 2,6-bis(pyrazol-1-yl)pyridine (bppCOOH) ligand results in the spin-crossover compound [Fe(bppCOOH)2](ClO4)2 which shows an abrupt spin transition with a T1/2 of ca. 380 K and a TLIESST of 60 K due to the presence of a hydrogen-bonded linear network of complexes.

A SIM-MOF: Three-Dimensional Organisation of Single-Ion Magnets with Anion-Exchange Capabilities

The formation of a metal-organic framework (MOF) with nodes that have single-molecule magnet (SMM) behaviour has been achieved by using mononuclear lanthanoid analogues, also known as single-ion magnets (SIMs), which enormously simplifies the challenging issue of making SMM-MOFs. Here we present a rational design of a family of MOFs, [Ln(bipyNO)4](TfO)3⋅x solvent (Ln=Tb (1); Dy (2); Ho (3); Er (4); TfO=triflate), in which the lanthanoid centres have an square-antiprismatic coordination environment suitable for SIM behaviour. Magnetic measurements confirm the existence of slow magnetic relaxation typical of SMMs, which has been rationalised by means of a radial effective charge model. In add…

Oxalate-based 2D magnets: the series [NBu4][MIIMnIII(ox)3] (MII= Fe, Co, Ni, Zn; ox = oxalate dianion)

The synthesis, structure and physical properties of the bimetallic oxalate-based molecular magnets containing MnIII of formula [NBu4][MIIMn(ox)3] (MII = Fe, Co, Ni, Zn; ox = oxalate dianion) are presented here. All compounds are isostructural, containing two-dimensional honeycomb bimetallic networks formed by alternating MII and MIII ions connected by oxalate anions. These compounds exhibit antiferromagnetic interactions that give rise to ferrimagnets or weak ferromagnets ordering at critical temperatures up to 21 K.

Inside Front Cover: Long-Living Light-Emitting Electrochemical Cells - Control through Supramolecular Interactions (Adv. Mater. 20/2008)

Tailoring magnetic properties of electrodeposited thin films of the molecule-based magnet Cr5.5(CN)12 11.5H2O

This paper reports on molecular-based magnetic thin films of Prussian blue analogues (PBA) with high critical temperatures composed of mixed-valence chromium cyanides. The thin films of PBA were synthesized by means of electrodeposition technique. Morphology and magnetic study are presented in a function of electrochemical deposition conditions. We present the electrochemical methods as a promising and effective tool for preparing molecular-based magnetic thin films of Prussian blue analogue.

Insertion of FeII complexes with Schiff base ligands derived from imidazole or pyridine into 3D bimetallic oxalate-based ferromagnets

Abstract The syntheses, structures and magnetic properties of the compounds [FeII(imid2-trien)][MnII(CH3OH)CrIII(ox)3]2·(CH3OH)4(CH3CN)(H2O) (1), [FeII(tren(6-Me-py)3)][MnIICrIII(ox)3][MnII(CH3OH)0.58(H2O)0.42CrIII(ox)3]·(CH3OH)2(CH3CN)0.5(H2O)0.42 (2) and [FeII(tren(imid)3)]2[Mn2.5(CH3OH)3Cr3(ox)9]·(CH3OH)4.75·(H2O)4.25 (3) are reported. They are prepared by the insertion of FeII-Schiff base complexes derived from imidazole and pyridine into bimetallic oxalate networks. Different types of 3D oxalate networks are obtained for each templating cation. Thus, [FeII(imid2-trien)]2+ and [FeII(tren(6-Me-py)3)]2+ give rise to unusual 3D achiral bimetallic oxalate networks with heptacoordinated MnII…

Efficient blue emitting organic light emitting diodes based on fluorescent solution processable cyclic phosphazenes

Solution processable blue fluorescent dendrimers based on cyclic phosphazene (CP) cores incorporating amino-pyrene moieties have been prepared and used as emissive layers in organic light emitting diodes (OLEDs). These dendrimers have high glass transition temperatures, are monodisperse, have high purity via common chromatographic techniques, and form defect-free amorphous films via spin/dip coating. The solution processable blue light emitting OLEDs reach current efficiencies of 3.9 cd/A at brightness levels near 1000 cd/m2. Depending on the molecular bridge used to attach the fluorescent dendron to the inorganic core, the emission wavelength changes from 470 to 545 nm, corresponding to bl…

Design of bimetallic magnetic chains based on oxalate complexes: towards single chain magnets

We describe the synthesis, structure and magnetic characterization of several oxalate-based bimetallic 1D systems. We will exemplify how by suitable choice of the molecular building blocks and strict control of their arrangement in the solid state, the magnetic properties of these low-dimensional materials can be tuned to finally obtain bimetallic oxalate chains behaving as single-chain magnets (SCM). First, we will focus on compounds [K(18-crown-6)][MII(bpy)Cr(ox)3] (1, 2; MII = Mn, Co; bpy = C10N2H8). The MnCr derivative behaves as a 1D ferromagnet down to 2 K, the lowest investigated temperature. The lack of magnetic ordering in this chain prompted us to prepare the more anisotropic MnCo…

Low-Frequency Imaginary Impedance at the Superconducting Transition of 2 H - Nb Se 2

Strain Switching in van der Waals Heterostructures triggered by a Spin-Crossover Metal Organic Framework

Van der Waals heterostructures (vdWHs) combine different layered materials with properties of interest,1 such as two-dimensional (2D) semimetals, semiconductors, magnets or superconductors. These heterostructures provide the possibility of engineering new materials with emergent functionalities that are not accessible in another way. Beyond inorganic 2D materials, layered molecular materials remain still rather unexplored, with only few examples regarding their isolation as atomically thin-layers. By a proper chemical design, the physical properties of these systems can be tuned, as illustrated by the so-called spin-crossover (SCO) compounds, in which a spin transition can be induced by app…

A pseudo-Jahn–Teller model of the photochromic effect in sodium nitroprusside

Abstract A new model for the photochromic effect in sodium nitroprusside Na2[Fe(CN)5(NO)]·2H2O based on the concept of the pseudo-Jahn–Teller effect is proposed. The model takes into account the electron transfer from the Fe2+ ion to the π* orbitals of the NO-ligand as well as the vibronic mixing of three electronic states of the Fe NO fragment through the non-symmetric and full-symmetric modes. The problem is solved within the adiabatic approximation. Under certain conditions the lower sheet of the adiabatic potential is shown to possess three minima with the increasing energies that correspond to the N-bound, sideways bound and O-bound NO group. The barriers between the minima are estimat…

Increased conductivity of a hole transport layer due to oxidation by a molecular nanomagnet

Thin film transistors based on polyarylamine poly?N,N?-diphenyl-N,N ?bis?4-hexylphenyl?- ?1,1?biphenyl?-4,4?-diamine ?pTPD? were fabricated using spin coating in order to measure the mobility of pTPD upon oxidation. Partially oxidized pTPD with a molecular magnetic cluster showed an increase in mobility of over two orders of magnitude. A transition in the mobility of pTPD upon doping could also be observed by the presence of a maximum obtained for a given oxidant ratio and subsequent decrease for a higher ratio. Such result agrees well with a previously reported model based on the combined effect of dipolar broadening of the density of states and transport manifold filling. Peer Reviewed

Tuning the nuclearity of iron(iii) polynuclear clusters by using tetradentate Schiff-base ligands

Three novel octanuclear, hexanuclear and tetranuclear complexes of high-spin Fe(III) ions were obtained by the reaction of the N,N′-bis-(1R-imidazol-4-ylmethylene)-ethane-1,2-diamine ligand (R = H, CH3) and its derivatives with Fe(ClO4)3·6H2O and KSCN. The tetradentate Schiff-base ligand acts as a bis(bidentate) chelating bridge between two adjacent high-spin Fe(III) centers. The presence of a methyl group in the imidazolyl substituent, the change of counterions or the replacement of imidazole by pyridine has a drastic effect on the nuclearity of the cluster. The magnetic properties of all compounds exhibit antiferromagnetic interactions via μ-oxo or μ-hydroxo pathways in Fe(III) dimers.

Mixed-Valence Molecular Unit for Quantum Cellular Automata: Beyond the Born-Oppenheimer Paradigm through the Symmetry-Assisted Vibronic Approach.

In this article, we focus on the electron-vibrational problem of the tetrameric mixed-valence (MV) complexes proposed for implementation as four-dot molecular quantum cellular automata (mQCA).1 Although the adiabatic approximation explored in ref 2 is an appropriate tool for the qualitative analysis of the basic characteristics of mQCA, like vibronic trapping of the electrons encoding binary information and cell-cell response, it loses its accuracy providing moderate vibronic coupling and fails in the description of the discrete pattern of the vibronic levels. Therefore, a precise solution of the quantum-mechanical vibronic problem is of primary importance for the evaluation of the shapes o…

Heptanuclear hydroxo-bridged copper cluster of the dicubane-like type: structural and magnetic characterisations of [Cu7(OH)6Cl2(pn)6(H2O)2](C(CN)3)4Cl2 (pn = 1,3-diaminopropane)

A new polynuclear copper(II) complex [Cu7(OH)6Cl2- (pn)6(H2O)2](C(CN)3)4Cl2 with hydroxo-bridging ligands has been prepared; the centrosymmetric cluster cation can be described as two Cu4O3Cl distorted cubane units sharing one copper cation. Clemente Juan, Juan Modesto, Juan.M.Clemente@uv.es ; Gomez Garcia, Carlos Jose, Carlos.Gomez@uv.es ; Coronado Miralles, Eugenio, Eugenio.Coronado@uv.es

Interplay between Chemical Composition and Cation Ordering in the Magnetism of Ni/Fe Layered Double Hydroxides

We report the synthesis of a family of ferrimagnetic NiFe layered double hydroxides (LDHs) with a variable Ni(2+)/Fe(3+) in-plane composition of [Ni(1-x)Fe(x)(OH)2](CO3)(x/2)·yH2O (x = 0.20, 0.25, and 0.33) by following a modified homogeneous precipitation. These layered magnets display high crystallinity, homogeneous hexagonal morphologies, and micrometric size that enable their quantitative exfoliation into single layers by sonomechanical treatment of the solids in polar solvents. This was confirmed by dynamic light scattering, UV-vis spectroscopy, high-resolution transmission electron miscroscopy, and atomic force microscopy methodologies to study the resulting steady suspensions. Our ma…

Single-Component Magnetic Conductors Based on Mo3S7 Trinuclear Clusters with Outer Dithiolate Ligands

A trinuclear cluster complex containing the Mo(3)S(7) central unit coordinated to dithiolate ligands, in particular the organic dmit (1,3-dithia-2-thione-4,5-dithiolate) anion, has been used to prepare a single-component molecular conductor formed by the threefold symmetry magnetic building block Mo(3)S(7)(dmit)(3) (1). The [Mo(3)S(7)(dmit)(3)](2)(-) ([1](2)(-)) diamagnetic anion forms dimers by interaction between the electrophilic cluster axial sulfur atoms and the sulfur atoms of the outer dithiolate ligand. Additional contacts between adjacent dmit ligands result in chain formation. The two-electron oxidation of [1](2)(-) yields to a three-dimensional molecular solid formed by neutral M…

Magnetic Exchange between Orbitally Degenerate Metal Ions: The Problem of Magnetic Anisotropy

Abstract In this paper we show that a strong magnetic anisotropy appears in exchange mixed–valence clusters containing orbitally degenerate metal ions. Combining an effective Hamiltonian approach with the technique of the irreducible tensor operators (ITO) and pseudoangular momentum representation we have solved the problem of magnetic exchange in localized and delocalized (mixed–valence) systems with different overall symmetries ( D 2 h , D 3 h , D 4 h ). The energy pattern as well as the character of the magnetic anisotropy is closely related to the ground term of the ions, electron transfer pathways, and overall symmetry of the system being affected also by the local crystal fields, spin…

In-Situ Growth of Ultrathin Films of NiFe-LDHs: Towards a Hierarchical Synthesis of Bamboo-Like Carbon Nanotubes

The synthesis of ultrathin films (UTFs) of NiFe-LDHs has been achieved by means of an in situ hydrothermal approach, leading to a flat disposition of the LDH crystallites on the substrate, in clear contrast to the most common perpendicular orientation reported to date. Experimental factors like time of synthesis or the nature of the substrate, seem to play a crucial role during the growing process. The 2D morphology of the NiFe-LDH crystallites was kept after a calcination procedure, leading to a topotactic transformation into mixed-metal oxide platelets. Hereby, in order to study the catalytic behavior of our samples, a chemical vapor deposition process is explored upon the as-synthesized …

Magnetoresistance studies of the ferromagnetic molecular metal (BEDT-TTF)3[MnCr(C2O4)3] under pressure

(BEDT-TTF)3[MnCr(C2O4)3] is the first ferromagnetic molecular metal, in which organic layers of BEDT-TTF alternate with infinite layers of the bimetallic oxalate complex [MnCr(C2O4)3]-. While the bimetallic layer undergoes a magnetic phase transition into a canted ferromagnetic state at 5.5 K, the metallic character of the conductivity is not affected by the magnetic transition [Nature 408 (2000) 447]. We performed magnetoresistance measurements (B≤17 T) at low temperatures (T≥900 mK) and under hydrostatic pressures of up to 2.0 GPa. Oscillations in the magnetoresistance develop under pressure that can be interpreted as Shubnikov-de Haas oscillations, if an internal magnetic field is taken …

Unusual Magnetic Behavior in the Layered Ferromagnet [Ni(C6H14N2)2]3[Fe(CN)6]2·2H2O

The cyano-bridged molecular complex [Ni(C6H14N2)2]3[Fe(CN)6]2·2H2O, with a rectangular 2D structure, displays long-range ferromagnetic ordering at 14 K, and exhibits unusual magnetic properties for this type of material, as confirmed by the appearance of two different peaks in the AC magnetic susceptibility plot, and a high coercive field (2.3 kOe) and remnant magnetization (6.8 μB). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Preface for the Forum on Molecular Magnetism: The Role of Inorganic Chemistry

Molecular magnetism is a rapidly expanding field of research whose central theme is the design and study of magnetic molecules and materials with tunable properties. In the early stages of the field, which began to take shape in the 1980s, much of the effort was directed at the pursuit of molecule-based magnetic solids that order at high temperatures. These materials are basically of two types: those based on tetracyanoethylene (TCNE) and those based on cyanide. As the field rapidly evolved over the past two decades, exciting new challenges appeared on the horizon, including the use of building block approaches for the preparation of complex multifunctional magnetic materials, the fabricati…

Molecule-based magnetic materials.

Current rectification in a single molecule diode: the role of electrode coupling.

We demonstrate large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 10^5 A/cm^2. By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions u…

Increasing the Nuclearity of Magnetic Polyoxometalates. Syntheses, Structures, and Magnetic Properties of Salts of the Heteropoly Complexes [Ni3(H2O)3(PW10O39)H2O]7-, [Ni4(H2O)2(PW9O34)2]10-, and [Ni9(OH)3(H2O)6(HPO4)2(PW9O34)3]16-

The rational synthesis and the structural and magnetic characterization of three different nickel clusters encapsulated in Keggin trivacant fragments are presented. The three complexes show how it is possible to increase the nuclearity of the clusters (from 3 and 4 to 9) by slightly changing the synthetic conditions. These three anionic clusters crystallize as mixed salts of K+ and Na+. The trimeric complex [Ni3(H2O)3PW10O39H2O]7- (Ni3) crystallizes in the triclinic space group P1 (a = 10.896(6) A, b = 12.869(5) A, c = 20.373(6) A, α = 94.67(6)°, β = 101.12(8)°, γ = 110.72(8)°, Z = 2) and presents a ferromagnetic triangular cluster. The tetranuclear complex [Ni4(H2O)2(PW9O34)2]10- (Ni4) cry…

Magnetic mixed-valence d2-d1-d1 trimers with partial electron delocalization: vibronic coupling and magnetic properties

Abstract The energy levels and magnetic properties of a triangular mixed-valence cluster d1-d1-d2 with electron delocalization in a pair of sites are examined from a model that takes into account electron transfer, magnetic exchange, and vibronic coupling. We show that the electron transfer process involves besides the usual double-exchange parameter, and additional parameter referred to as exchange transfer. This last parameter accounts for the interaction between the moving electron of the mixed valence pair and the electron localized in the third side. We notice that the role of double exchange is to stabilize a ferromagnetic alignment of the spins on the mixed-valence pair. A comparison…

ChemInform Abstract: Hybrid Materials Based on Magnetic Layered Double Hydroxides: A Molecular Perspective

ConspectusDesign of functional hybrids lies at the very core of synthetic chemistry as it has enabled the development of an unlimited number of solids displaying unprecedented or even improved properties built upon the association at the molecular level of quite disparate components by chemical design. Multifunctional hybrids are a particularly appealing case among hybrid organic/inorganic materials. Here, chemical knowledge is used to deploy molecular components bearing different functionalities within a single solid so that these properties can coexist or event interact leading to unprecedented phenomena. From a molecular perspective, this can be done either by controlled assembly of orga…

Exchange coupling in an electrodeposited magnetic bilayer of Prussian blue analogues

Bilayers of Prussian blue analogues (PBA) constituted of hard and soft magnets have been fabricated by means of electrochemical deposition. This method affords a good contact between two PBA thin films of nanometer thickness. Complete characterization of the resulting system has been performed, which has allowed the determination of the preservation of the chemical identity of both materials during the electrodeposition and the establishment of a clear interface between them. The magnetic behavior of the bilayer can be explained in terms of an exchange-spring magnet.

Plasmon-assisted spin transition in gold nanostar@spin crossover heterostructures

Aquí presentamos el diseño de nanopartículas core@shell formadas por un núcleo de nanoestrella de Au metálico y una capa cruzada de espín basada en el polímero de coordinación [Fe(Htrz)2(trz)](BF4). Este procedimiento es general y se ha extendido a otras morfologías metálicas (nanovarillas, nanotriángulos). Gracias al efecto fototérmico derivado de las propiedades plasmónicas de la nanoestrella de Au, el 60 % de los centros de hierro experimentan una transición de espín térmico dentro de la histéresis térmica provocada por una irradiación de baja intensidad con un láser de 808 nm. En comparación con otras morfologías de Au, la gran ventaja de la forma de nanoestrella surge de los puntos cal…

Functional Hybrid Materials Containing Polypyrrole and Polyoxometalate Clusters: Searching for High Conductivities and Specific Charges

Switching the Magnetic Vortex Core in a Single Nanoparticle.

Imaging and manipulating the spin structure of nano- and mesoscale magnetic systems is a challenging topic in magnetism, yielding a wide range of spin phenomena such as skyrmions, hedgehog-like spin structures, or vortices. A key example has been provided by the vortex spin texture, which can be addressed in four independent states of magnetization, enabling the development of multibit magnetic storage media. Most of the works devoted to the study of the magnetization reversal mechanisms of the magnetic vortices have been focused on micrometer-size magnetic platelets. Here we report the experimental observation of the vortex state formation and annihilation in individual 25 nm molecular-bas…

Energy Storage: Giant Enhancement in the Supercapacitance of NiFe–Graphene Nanocomposites Induced by a Magnetic Field (Adv. Mater. 28/2019)

Iron(ii) complexes of tris(2-pyridylmethyl)amine (TPMA) and neutral bidentate ligands showing thermal- and photo-induced spin crossover

Three new mononuclear Fe(ii) complexes have been prepared and characterized by the combination of tetradentate tris(2-pyridylmethyl)amine (TPMA) with three neutral bidentate ligands, such as ethylenediamine (en), 1,2-diaminopropane (pn) and 2-picolylamine (2-pic), in compounds [FeII(TPMA)(en)](ClO4)2 (1), [FeII(TPMA)(2-pic)](ClO4)2 (2) and [FeII(TPMA)(pn)](ClO4)2 (3). Structural and magnetic characterization demonstrates that the three compounds present a complete SCO behavior. The absence of strong intermolecular interactions and solvent molecules leads to reversible and gradual spin transitions. The different ligands allow tuning T1/2 from 130 K (2) to 325 K (3). The compound with the low…

A decacobalt(ii) cluster with triple-sandwich structure obtained by partial reductive hydrolysis of a pentacobalt(ii/iii) Weakley-type polyoxometalate.

Partial reductive hydrolysis of a penta-CoII/III cluster [CoII4(H2O)2(CoIIIW9O34)(PW9O34)]12− (1) leads to the formation of [Co2{Co3(H2O)(Co(OH)2W7O26)(PW9O34)}2]22− (2). This polyoxometalate is made up of two capping [PW9O34]9− units and two bridging [W7O26]10− units that assemble to encapsulate a novel deca-CoII cluster core comprising octahedral and tetrahedral CoII ions.

Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2H−TaS2

The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides $2H\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density wave is found to collapse at 8.5 GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5 GPa. Our report constitutes a new observation of such Raman active H…

Study of charge density waves in suspended 2H-TaS 2 and 2H-TaSe 2 by nanomechanical resonance

The charge density wave (CDW) state in van der Waals systems shows interesting scaling phenomena as the number of layers can significantly affect the CDW transition temperature, $T_{CDW}$. However, it is often difficult to use conventional methods to study the phase transition in these systems due to their small size and sensitivity to degradation. Degradation is an important parameter which has been shown to greatly influence the superconductivity in layered systems. Since the CDW state competes with the onset of superconductivity, it is expected that $T_{CDW}$ will also be affected by the degradation. Here, we probe the CDW phase transition by the mechanical resonances of suspended 2H-TaS…

Magnetic molecular metals based on the organic donor molecule BET (BET = Bis(ethylenethio)tetrathiafulvalene): The series BET2[MCI4] (M3⊕= Ga, Fe)

Molecular hybrids formed by oxalate bridged dinuclear anions and organometallic cations

Abstract The syntheses, magnetic properties and infrared spectra of a new series of molecular hybrids formed by association of two magnetic sublattices: (i) oxalate bridged dinuclear anions [V 2 O 2 (ox)(NCS) 6 ] 4− and [M′M′'(ox)(NCS) 8 ] 4 ( M′= Fe III , Cr III ; M′' - Fe III , Cr III ; ox 2 = C 2 O 4 2 and (ii) decamethylferrocenium organometallic cation are presented. The crystal structure of [Fe(Cp * ) 2 ][(C 2 H 5 ) 4 N] 2 [V 2 O 2 (ox)(NCS) 6 ] is also discussed.

Classical-spin approach to a magnetic comb-like chain: application to the two-sublattice chain compound MnMn(CDTA)·7H2O

Abstract We report on the magnetic properties of the two-sublattice manganese chain MnMn(CDTA)·7H 2 O. In view of the structural features, this compound may give rise to a novel type of one-dimensional magnetic network formed by a chain of exchange coupled triangles. A classical-spin model that considers two magnetic sites coupled through two different and isotropic exchange interactions is developed and used in order to analyze the magnetic properties of this compound. The possibility of having a spinfrustration is also examined.

Prussian blue@MoS2 layer composites as highly efficient cathodes for sodium- and potassium-ion batteries

Prussian blue (PB) represents a simple, economical, and eco‐friendly system as cathode material for sodium‐ion batteries (SIBs). However, structural problems usually worsen its experimental performance thus motivating the search for alternative synthetic strategies and the formation of composites that compensate these deficiencies. Herein, a straightforward approach for the preparation of PB/MoS2‐based nanocomposites is presented. MoS2 provides a 2D active support for the homogeneous nucleation of porous PB nanocrystals, which feature superior surface areas than those obtained by other methodologies, giving rise to a compact PB shell covering the full flake. The nanocomposite exhibits an ex…

Boosting the supercapacitive behavior of CoAl-layered double hydroxides via tuning the metal composition and interlayer space

Layered double hydroxides (LDHs) are promising supercapacitor materials due to their wide chemical versatility, earth abundant metals and high specific capacitances. Many parameters influencing the supercapacitive performance have been studied such as the chemical composition, the synthetic approaches, and the interlayer anion. However, no systematic studies about the effect of the basal space have been carried out. Here, two-dimensional (2D) CoAl-LDHs were synthesized through anion exchange reactions using surfactant molecules in order to increase the interlayer space (ranging from 7.5 to 32.0 Å). These compounds exhibit similar size and dimensions but different basal space to explore excl…

Single-Crystal-to-Single-Crystal Anion Exchange in a Gadolinium MOF: Incorporation of POMs and [AuCl4]−

The encapsulation of functional molecules inside porous coordination polymers (also known as metal-organic frameworks, MOFs) has become of great interest in recent years at the field of multifunctional materials. In this article, we present a study of the effects of size and charge in the anion exchange process of a Gd based MOF, involving molecular species like polyoxometalates (POMs), and [AuCl4]−. This post-synthetic modification has been characterized by IR, EDAX, and single crystal diffraction, which have provided unequivocal evidence of the location of the anion molecules in the framework.

Correction of the tip convolution effects in the imaging of nanostructures studied through scanning force microscopy

AFM images are always affected by artifacts arising from tip convolution effects, resulting in a decrease in the lateral resolution of this technique. The magnitude of such effects is described by means of geometrical considerations, thereby providing better understanding of the convolution phenomenon. We demonstrate that for a constant tip radius, the convolution error is increased with the object height, mainly for the narrowest motifs. Certain influence of the object shape is observed between rectangular and elliptical objects with the same height. Such moderate differences are essentially expected among elongated objects; in contrast they are reduced as the object aspect ratio is increa…

Design of high-temperature f-block molecular nanomagnets through the control of vibration-induced spin relaxation† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c9sc03133b

An efficient general first-principles methodology to simulate vibration-induced spin relaxation in f-block molecular nanomagnets that drastically reduces the computation time.

CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties

The gram-scale synthesis of carbon spheres with a diameter of ca. 740 nm has been achieved by means of a chemical vapour deposition method using NiFe-layered double hydroxides as a solid catalytic precursor. The presence of the catalyst (FeNi3) allows controlling the final size distribution, resulting in a monodisperse sample. Their structural properties exhibited a high degree of graphitization according to their ID/IG ratio. In addition, their morphological features were unveiled by FIB-SEM and HRTEM, showing that they are formed by solid inner cores, and presenting labile chain-like structures due to accretion procedures. The solution and posterior sonication of the samples in toluene ga…

Observation of electroluminescence at room temperature from a ruthenium(II) bis-terpyridine complex and its use for preparing light-emitting electrochemical cells.

A terpyridine ruthenium (II) complex containing a substituted and an unsubstituted terpyridine ligand was synthesized, and its luminescence properties were studied in a solid-state single-layer light-emitting electrochemical cell. The obtained devices emitted light of a very deep red color (CIE, x = 0.717 y = 0.282) at low external applied bias. It is the first example of an electroluminescence device based on a bis-chelated ruthenium complex. Its ambient atmosphere decay is remarkably different from analogous devices using tris-chelated ruthenium complexes.

Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization

Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional (2D) materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust and magnetic functionalized monolayers of coordination polymers. A series of five isostructural layered magnetic coordination polymers based on Fe(ii) centres a…

Polyoxometalates: From Magnetic Models to Multifunctional Materials

In this article we have presented some recent achievements of the polyoxometalates in the fields of molecular magnetism and functional molecular materials. In the context of the molecular magnetism we have shown that POMs provide ideal examples of magnetic clusters with coexisting ferro and antiferromagnetic exchange interactions which can be investigated using a variety of magnetic techniques, including the Inelastic Neutron Scattering spectroscopy, to get a thorough characterization of the magnetic levels in these large clusters, and to test the validity of the spin hamiltonians commonly used in magnetism.

Nanofabrication of TaS2 conducting layers nanopatterned with Ta2O5 insulating regions via AFM

It is demonstrated how local oxidation nanolithography performed with an atomic force microscope (AFM-LON) may be successfully employed for the nanopatterning of insulating regions of Ta2O5 on TaS2 ultrathin metallic layers. This provides a simple approach for the fabrication of electronic devices, such as single-electron transistors, at the nanoscale.

[MnM(egta)]· 8H2O(M= Mn, Cd): A Novel Type of Two-Dimensional Magnetic Lattice

Two Consecutive Magneto-Structural Gas-Solid Transformations in Non-Porous Molecular Materials

Modification of the magnetic properties in a solid-state material upon external stimulus has attracted much attention in the recent years for their potential applications as switches and sensors. Within the field of coordination polymers, gas sorption studies typically focus on porous solids, with the gas molecules accommodating in the channels. Here we present a 1D non-porous coordination polymer capable of incorporating HCl gas molecules, which not only causes a reordering of its atoms in the solid state but also provokes dramatic changes in the magnetic behavior. Subsequently, a further solid-gas transformation can occur with the extrusion of HCl gas molecules causing a second structural…

MAGPACK1A package to calculate the energy levels, bulk magnetic properties, and inelastic neutron scattering spectra of high nuclearity spin clusters

Anisotropic double exchange in orbitally degenerate mixed valence systems

Abstract The problem of the double exchange is considered for the mixed valence dimers in which one or both transition metal ions possess orbitally degenerate ground states. In the pseudo-angular momentum representation, the general formula is deduced for the matrix elements of double exchange involving the transfer integrals and all spin and orbital quantum numbers. The pairs 3 T 1 t 2 2 – 2 T 2 t 2 1 and 3 T 1 t 2 2 – 4 A 2 t 2 3 are considered in three high-symmetric topologies: edge-shared D2h, corner-shared D4h, and face-shared D3h bioctahedra. The double exchange in orbitally degenerate systems is shown to produce strong magnetic anisotropy of an orbital nature. The character of the a…

Experimental determination of single molecule toroic behaviour in a Dy8 single molecule magnet

The enhancement of toroic motifs through coupling toroidal moments within molecular nanomagnets is a new, interesting and relevant approach for both fundamental research and potential quantum computation applications. We investigate a Dy8 molecular cluster and discover it has a antiferrotoroic ground state with slow magnetic relaxation. The experimental characterization of the magnetic anisotropy axes of each magnetic center and their exchange interactions represents a considerable challenge due to the non-magnetic nature of the toroidal motif. To overcome this and obtain access to the low energy states of Dy8 we establish a multi-orientation single-crystal micro Hall sensor magnetometry ap…

Cubane-Type Mo3CoS4 Molecular Clusters with Three Different Metal Electron Populations: Structure, Reactivity and Their Use in the Synthesis of Hybrid Charge-Transfer Salts

Heterodimetallic cubane-type complexes coordinated to diphosphanes [Mo(3)CoS(4)(dmpe)(3)Cl(4)](+) ([1](+)) (dmpe=1,2-bis(dimethylphosphanyl)ethane), [Mo(3)CoS(4)(dmpe)(3)Cl(4)] (1) and [Mo(3)CoS(4)(dmpe)(3)Cl(3)(CO)] (2) with 14, 15 and 16 metal electrons, respectively, have been prepared from the [Mo(3)S(4)(dmpe)(3)Cl(3)](+) trinuclear precursor using [Co(2)(CO)(8)] or CoCl(2) as cobalt source. Cluster complexes [1](+) and 1 are easily interconverted chemically and electrochemically. The Co-Cl distance increases upon electron addition and substitution of the chlorine atom coordinated to cobalt with CO only takes place in presence of a reducing agent to give complex 2. Structural changes in…

Macrocycle-Based Spin-Crossover Materials

International audience; New iron(II) complexes of formula [Fe(L1)](BF(4))(2) (1) and [Fe(L2)](BF(4))(2) x H(2)O (2) (L1 = 1,7-bis(2'-pyridylmethyl)-1,4,7,10-tetraazacyclododecane; L2 = 1,8-bis(2'-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized by infrared spectroscopy, variable-temperature single-crystal X-ray diffraction, and variable-temperature magnetic susceptibility measurements. The crystal structure determinations of 1 and 2 reveal in both cases discrete iron(II) monomeric structures in which the two functionalized tetraazamacrocycles (L1 and L2) act as hexadentate ligands; the iron(II) ions are coordinated with six nitrogen atoms: four from …

Inverted Solution Processable OLEDs Using a Metal Oxide as an Electron Injection Contact.

A new type of bottom-emission electroluminescent device is described in which a metal oxide is used as the electron-injecting contact. The preparation of such a device is simple. It consists of the deposition of a thin layer of a metal oxide on top of an indium tin oxide covered glass substrate, followed by the solution processing of the light-emitting layer and subsequently the deposition of a high-workfunction (air-stable) metal anode. This architecture allows for a low-cost electroluminescent device because no rigorous encapsulation is required. Electroluminescence with a high brightness reaching 5700 cd m–2 is observed at voltages as low as 8 V, demonstrating the potential of this new a…

Spin dynamics in the single-ion magnet [Er(W5O18)2]9−

In this work we present a detailed NMR and ${\ensuremath{\mu}}^{+}\mathrm{SR}$ investigation of the spin dynamics in the new hydrated sodium salt containing the single-ion magnet ${[\mathrm{Er}{({\mathrm{W}}_{5}{\mathrm{O}}_{18})}_{2}]}^{9\ensuremath{-}}$. The $^{1}\mathrm{H}\phantom{\rule{0.16em}{0ex}}\mathrm{NMR}$ absorption spectra at various applied magnetic fields present a line broadening on decreasing temperature which indicates a progressive spin freezing of the single-molecule magnetic moments. The onset of quasistatic local magnetic fields, due to spin freezing, is observed also in the muon relaxation curves at low temperature. Both techniques yield a local field distribution of t…

Quantum computing with molecular spin systems

Molecular spintronics promises to combine the flexibility offered by synthetic chemistry with the advantages of an electronics which is based on the electron spin rather than its charge degree of freedom. Here, we review recent work on the description of transport across molecular spin systems and on a proposal for an all-electrical scheme for the implementation of a fundamental two-qubit gate in a certain class of molecular systems.

Double Exchange in Orbitally Degenerate Mixed Valence Clusters: Magnetic Anisotropy, Vibronic Effects

In this paper we consider the vibronic problem of the double exchange in mixed-valence dimers containing transition metal ions in orbitally degenerate ground states. The vibronic model includes interaction with the breathing local modes (Piepho-Krausz-Schatz-PKS) as well as the modulation of metal-metal distances as suggested by Piepho. The double exchange in orbitally degenerate systems is shown to produce strong magnetic anisotropy of orbital nature. PKS interaction is expected to suppress the magnetic anisotropy of the system, while the intercenter vibrations tend to enhance it. The roles of spin-orbit coupling and temperature are revealed for the systems with different geometries.

Enhancing coherence in molecular spin qubits via atomic clock transitions

Quantum computing is an emerging area within the information sciences revolving around the concept of quantum bits (qubits). A major obstacle is the extreme fragility of these qubits due to interactions with their environment that destroy their quantumness. This phenomenon, known as decoherence, is of fundamental interest1,2. There are many competing candidates for qubits, including superconducting circuits3, quantum optical cavities4, ultracold atoms5 and spin qubits6,7,8, and each has its strengths and weaknesses. When dealing with spin qubits, the strongest source of decoherence is the magnetic dipolar interaction9. To minimize it, spins are typically diluted in a diamagnetic matrix. For…

Problem of the magnetic anisotropy in orbitally degenerate exchange and mixed-valence clusters

Abstract This contribution summarizes the results obtained in the problem of orbital degeneracy of the metal ions in exchange coupled and mixed-valence (MV) clusters. The theory of the double exchange is generalized and the orbitally degenerate systems are considered. The orbitally dependent double exchange parameter is deduced for the singlet–triplet and triplet–triplet transition metal pairs in three high-symmetric topologies. A new effective Hamiltonian of the magnetic exchange between the ions with unquenched orbital angular momenta is discussed. The technique of the irreducible tensor operators is applied to the problem of the kinetic exchange in these kind of metal clusters. Strong ma…

Langmuir monolayers and Langmuir–Blodgett films of ferritin prepared by using a surfactant mixture of eicosylamine (EA) and methyl stearate (SME)

Abstract Magnetic Langmuir–Blodgett films of ferritin have been prepared by using the adsorption properties of a 1/4 mixed monolayer of eicosylamine (EA) and methyl stearate (SME). BAM images show that a more homogeneous distribution of ferritin at the air–water interface is achieved by using this mixture of surfactants instead of the DODA/SME mixed matrix of a previous work. Transfer of the monolayer onto different substrates allowed the preparation of multilayer LB films. Infrared and UV–Vis spectroscopies indicate that ferritin molecules are incorporated within the LB films. Furthermore, UV–Vis spectroscopy measurements reveal that the amount of ferritin incorporated into these LB film h…

Spin crossover complexes as building units of hydrogen-bonded nanoporous structures

The paper reports on the synthesis, crystal structure, differential scanning calorimetry (DSC) and magnetic properties of a spin crossover salt of formula [Fe(bpp)2](cis,cis-1,3,5-Hchtc)·5.5 H2O (1) (bpp = 2,6-bis(pyrazol-3yl)pyridine; cis,cis-1,3,5-Hchtc = monoprotonated cyclohexanetricarboxylate dianion). The salt shows a porous structure with water molecules sitting in the channels. The electronic configuration of the Fe2+ ions is high-spin (HS). Desolvation of 1 yields a material exhibiting an abrupt spin crossover with a thermal hysteresis loop located near room temperature (T1/2↑ = 319 K and T1/2↓ = 309 K). Rehydration of this desolvated salt yields an essentially low-spin (LS) materi…

Enhanced superconductivity in atomically thin TaS2

The ability to exfoliate layered materials down to the single layer limit has presented the opportunity to understand how a gradual reduction in dimensionality affects the properties of bulk materials. Here we use this top–down approach to address the problem of superconductivity in the two-dimensional limit. The transport properties of electronic devices based on 2H tantalum disulfide flakes of different thicknesses are presented. We observe that superconductivity persists down to the thinnest layer investigated (3.5 nm), and interestingly, we find a pronounced enhancement in the critical temperature from 0.5 to 2.2 K as the layers are thinned down. In addition, we propose a tight-binding …

Effect of Metal Complexation on the Conductance of Single-Molecular Wires Measured at Room Temperature

The present work aims to give insight into the effect that metal coordination has on the room-temperature conductance of molecular wires. For that purpose, we have designed a family of rigid, highly conductive ligands functionalized with different terminations (acetylthiols, pyridines, and ethynyl groups), in which the conformational changes induced by metal coordination are negligible. The single-molecule conductance features of this series of molecular wires and their corresponding Cu(I) complexes have been measured in break-junction setups at room temperature. Experimental and theoretical data show that no matter the anchoring group, in all cases metal coordination leads to a shift towar…

Multifunctional magnetic materials obtained by insertion of spin-crossover Fe(III) complexes into chiral 3D bimetallic oxalate-based ferromagnets.

The syntheses, structures, and magnetic properties of compounds of formula [Fe(III)(5-Clsal(2)-trien)][Mn(II)Cr(III)(ox)(3)]·0.5(CH(3)NO(2)) (1), [Fe(III)(5-Brsal(2)-trien)][Mn(II)Cr(III)(ox)(3)] (2), and [In(III)(5-Clsal(2)-trien)][Mn(II)Cr(III)(ox)(3)] (3) are reported. The structure of the three compounds, which crystallize in the orthorhombic P2(1)2(1)2(1) chiral space group, presents a 3D chiral anionic network formed by Mn(II) and Cr(III) ions linked through oxalate ligands with inserted [Fe(III)(5-Clsal(2)-trien)](+), [Fe(III)(5-Brsal(2)-trien)](+), and [In(III)(5-Clsal(2)-trien)](+) cations. The magnetic properties indicate that the three compounds undergo long-range ferromagnetic o…

Nonanuclear Spin-Crossover Complex Containing Iron(II) and Iron(III) Based on a 2,6-Bis(pyrazol-1-yl)pyridine Ligand Functionalized with a Carboxylate Group.

The synthesis and magnetostructural characterization of [Fe(III)3(μ3-O)(H2O)3[Fe(II)(bppCOOH)(bppCOO)]6](ClO4)13·(CH3)2CO)6·(solvate) (2) are reported. This compound is obtained as a secondary product during synthesis of the mononuclear complex [Fe(II)(bppCOOH)2](ClO4)2 (1). The single-crystal X-ray diffraction structure of 2 shows that it contains the nonanuclear cluster of the formula [Fe(III)3(μ3-O)(H2O)3[Fe(II)(bppCOOH)(bppCOO)]6](13+), which is formed by a central Fe(III)3O core coordinated to six partially deprotonated [Fe(II)(bppCOOH)(bppCOO)](+) complexes. Raman spectroscopy studies on single crystals of 1 and 2 have been performed to elucidate the spin and oxidation states of iron …

Design of Magnetic Polyoxometalates for Molecular Spintronics and as Spin Qubits

Abstract In the past decades, POMs have been used as minimal models in Molecular Magnetism, since they are a convenient playing ground to study fundamental phenomena such as anisotropic magnetic exchange and electron transfer. Now they have jumped to the stage of the rational design of single-ion magnets and are being considered as test subjects for simple experiments in Single-Molecule Spintronics and Molecular Quantum Computing. This chapter contains an overview of recent results that demonstrate the potential of POMs in these emerging fields.

TCNQ radical salts containing magnetic complexes: Different interaction modes of TCNQ with Copper tetraazamacrocycles

Abstract This work is devoted to the study of compounds [M(N 4 )](TCNQ) n , where N 4 = saturated or unsaturated tetraazamacrocycles, TCNQ= 7,7,8,8-tetracyanoquinodimethane, n= 2, 3. The metal is coordinated to two TCNQ groups only when there is coordinative unsaturation on it. When n= 2 all the TCNQ units are radical anions and no charge delocalization is observed. In the compounds with n= 3 only 2 3 of the TCNQ are negatively charged and a greater charge delocalization is possible. This delocalization only appears when none of the TCNQ's are coordinated to the metal and it is reflected in the higher conductivity values obtained in the solid state.

Copper(I) pseudorotaxane monolayers assembled on gold electrodes.

Two new copper (I) pseudorotaxanes bearing a thioctic acid appended unit have been prepared and deposited onto a gold electrode surface, leading to surface-attached electroactive pseudorotaxanes.

Jahn-Teller effect in molecular electronics: quantum cellular automata

The article summarizes the main results of application of the theory of the Jahn-Teller (JT) and pseudo JT effects to the description of molecular quantum dot cellular automata (QCA), a new paradigm of quantum computing. The following issues are discussed: 1) QCA as a new paradigm of quantum computing, principles and advantages; 2) molecular implementation of QCA; 3) role of the JT effect in charge trapping, encoding of binary information in the quantum cell and non-linear cell-cell response; 4) spin-switching in molecular QCA based on mixed-valence cell; 5) intervalence optical absorption in tetrameric molecular mixed-valence cell through the symmetry assisted approach to the multimode/mul…

Magnetic Langmuir–Blodgett films of ferritin with different iron loadings

Abstract Magnetic Langmuir–Blodgett multilayers of two ferritin molecules 1 and 2 , containing, respectively, 4220 and 3062 Fe atoms have been prepared by using the adsorption properties of a 6/1 mixed monolayer of dioctadecyldimethylammonium bromide (DODABr) and methyl stearate (SME). Transfer ratios close to unity were reached giving rise to LB films with a strong red colour. Infrared and UV–vis spectroscopy indicates that ferritin molecules are incorporated within the LB films. Magnetic measurements show that the superparamagnetic properties of these molecules are preserved. Thus, a marked hysteresis loop of magnetisation is obtained for LB films of 1 and 2 with a coercive field of 3400 …

Magneto-optical Investigations of Nanostructured Materials Based on Single Molecule Magnets Monitor Strong Environmental Effects

The determination of the magnetic properties of molecular magnets in environments similar to those used in spintronic devices is fundamental for the development of applications. Single-molecule magnets (SMMs) are molecular cluster systems that display magnetic hysteresis of dynamical origin at low temperature. As they behave like perfectly monodisperse nanomagnets and show clear macroscopic quantum effects in their magnetic properties, they are extremely appealing candidates for the forthcoming generation of molecular devices: they have been proposed as efficient systems for quantum computation, ultra-high-density magnetic recording media, and molecular spintronic systems. These attractive …

Cover Picture: Nanoscale Deposition of Single-Molecule Magnets onto SiO2 Patterns (Adv. Mater. 2/2007)

The cover shows a schematic of scanning probe nanolithography based on the spatial confinement of an oxidation reaction within a water meniscus, and its application for fabricating ordered arrays of cationic Mn12 single-molecule magnets. Romero, Coronado, Garcia, and co-workers report on p. 291 that electrostatic interactions between the molecules and trapped charges within the nanodots drive the positioning of the molecules at the nanoscale.

Brief encounter at the molecular level: what muons tell us about molecule-based magnets

Abstract Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin–1/2, a lifetime of 2.2 μ S , about one-ninth of the proton mass and a magnetic moment of approximately 1/200 μ B . Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a…

The design of magneto-plasmonic nanostructures formed by magnetic Prussian Blue-type nanocrystals decorated with Au nanoparticles.

Abstract: We have developed a general protocol for the preparation of hybrid nanostructures formed by nanoparticles (NPs) of molecule-based magnets based on Prussian Blue Analogues (PBAs) decorated with plasmonic Au NPs of different shapes. By adjusting the pH, Au NPs can be attached preferentially along the edges of the PBA or randomly on the surface. The protocol allows tuning the plasmonic properties of the hybrids in the whole visible spectrum.

A neutral 2D oxalate-based soluble magnet assembled by hydrogen bonding interactions

Abstract Herein we describe the synthesis, structure and magnetic properties of a novel oxalate-based layered magnetic system: {[Mn(OH2)2(S)2][Mn(S)(OH2)]2[Cr(ox)3]2(18-crown-6)}∞ (S = CH3OH; ox = C 2 O 4 2 - ; 18-crown-6 = C12H24O6) (1). In this case, no cationic templating agent is required to promote the assembling of low-dimensional oxalate-bridged metallic complexes in solution. Instead, strong enough hydrogen bonding interactions are responsible for their packing in the solid state. This magnet is soluble and presents two different types of oxalate bridges: the common bis(bidentate) and the unusual bidentate–monodentate. This structural feature has drastic consequences on the magnetis…

Anisotropic exchange coupling in the Keggin derivative K8[Co2(D2O)(W11O39)] · n D2O

Abstract 20 g of the fully deuterated title compound have been prepared in polycrystalline form and investigated by inelastic neutron scattering using both thermal and cold neutrons. Magnetic dimer excitations were observed and the energy-splitting pattern resulting from the exchange coupling within the Co 2+ dimer was determined. The coupling is highly anisotropic with the parameter values J =−2.24 meV and η =0.33 based on the effective coupling Hamiltonian H =−2J[S 1z S 2z +η(S 1x S 2x +S 1y S 2y )] . The anisotropy results mainly from the single-ion anisotropy of the Co 2+ ion in the distorted octahedral coordination.

Polycationic Mn12Single-Molecule Magnets as Electron Reservoirs withS>10 Ground States

Electronic and Magnetic Study of Polycationic Mn-12 Single-Molecule Magnets with a Ground Spin State S=11

International audience; The preparation, magnetic characterization, and X-ray structures of two polycationic Mn-12 single-molecule magnets (Mn12O12(bet)(16)(EtOH)(4)](PF6)(14)center dot 4CH(3)CN center dot H2O (1) and [Mn12O12(bet)(16)(EtOH)(3)(H2O)](PF6)(13)(OH)center dot 6CH(3)CN center dot EtOH center dot H2O (2) (bet = betaine = (CH3)(3)N+-CH2-CO2-) are reported. 1 crystallizes in the centrosymmetric P2/cspace group and presents a (0:2:0:2) arrangement of the EtOH molecules in its structure. 2 crystallizes in the noncentrosymmetric P (4) over bar space group with two distinct Mn-12 polycations, [Mn12O12(bet)(16)(EtOH)(2)(H2O)(2)](14+) (2A) and [Mn12O12(bet)(16)(EtOH)(4)](14+)(2B) per un…

Metal complexes of a picolinate-based nitronyl nitroxide free radical.

A nitronyl nitroxide free radical containing an appended picolinate moiety was synthesized. The resulting tridentate ligand picNN forms neutral mononuclear metal complexes of formula [M(picNN)(2)].3H(2)O (M = Mn, Co, Ni, Zn). These compounds are isostructural and crystallize in the orthorhombic Pnna space group. The metal complexes have a C(2) symmetric structure, with the metal centers lying on the binary axis and surrounded by two equivalent picNN radicals. The magnetic properties of this family of compounds indicate the presence of very strong metal-radical exchange interactions, ranging from J(Ni-rad) = -193 cm(-1) to J(Mn-rad) = -98 cm(-1). Relatively weak (J(rad-rad) = -15 cm(-1)) thr…

Mixed-valence molecular four-dot unit for quantum cellular automata: Vibronic self-trapping and cell-cell response

Our interest in this article is prompted by the vibronic problem of charge polarized states in the four-dot molecular quantum cellular automata (mQCA), a paradigm for nanoelectronics, in which binary information is encoded in charge configuration of the mQCA cell. Here, we report the evaluation of the electronic levels and adiabatic potentials of mixed-valence (MV) tetra-ruthenium (2Ru(ii) + 2Ru(iii)) derivatives (assembled as two coupled Creutz-Taube complexes) for which molecular implementations of quantum cellular automata (QCA) was proposed. The cell based on this molecule includes two holes shared among four spinless sites and correspondingly we employ the model which takes into accoun…

A two-dimensional radical salt based upon BEDT-TTF and the dimeric, magnetic anion [Fe(tdas)2]22−: (BEDT-TTF)2[Fe(tdas)2] (tdas = 1,2,5-thiadiazole-3,4-dithiolate)

In an attempt to synthesize new synthetic metals which couple magnetic properties to conductivity, we prepared the novel salt (BEDT-TTF)2[Fe(tdas)2] [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, hereafter referred to as ET; tdas = 1,2,5-thiadiazole-3,4-dithiolate] by the electrocrystallization technique. The crystal structure of this compound, as determined by single crystal X-ray diffraction, contains conducting, organic ET layers separated by dimerized, magnetic [Fe(tdas)2]22− anions. Due to the magnetic insulating ground electronic state of the ET layer, thermally activated conductivity is observed, with a room temperature value of about 1 S cm−1. This salt was also characterized by…

ChemInform Abstract: Dynamic Magnetic MOFs

In this review we combine the use of coordination chemistry with the concepts of molecular magnetism to design magnetic Metal–Organic Frameworks (MOFs) in which the crystalline network undergoes a dynamic change upon application of an external stimulus. The various approaches so far developed to prepare these kinds of chemically or physically responsive MOFs with tunable magnetic properties are presented.

Single ion magnets based on lanthanoid polyoxomolybdate complexes

Polyoxometalate (POM) chemistry has recently offered excellent examples of single ion magnets (SIMs) and molecular spin qubits. Compared with conventional coordination compounds, POMs provide rigid and highly symmetric coordination sites. However, all POM-based SIMs reported to date exhibit a very limited range of possibilities for chemical processability. We present herein two new families of POM-based SIMs which are soluble in organic solvents: [Ln(β-Mo8O26)2]5− {LnIII = Tb, Dy, Ho, Er, Tm and Yb} and the functionalised POMs [Ln{Mo5O13(OMe)4NNC6H4-p-NO2}2]3− {LnIII = Tb, Dy, Ho, Er, Yb and Nd}. In addition, these two families represent the first SIMs based on polyoxomolybdates. A magneto-…

Electric Field Control of Spin-Dependent Dissipative Electron Transfer Dynamics in Mixed-Valence Molecules

We demonstrate that the borderline class II/III magnetic MV dimers, which can be referred to as single molecule multiferroics, provide a unique possibility to achieve electric field control of the electron transfer (ET) dynamics. As an example, we consider a MV dimer d2-d1 in which an extra electron is delocalized over two spin-cores (s0 = 1/2), and the ET is spin-dependent due to the double exchange mechanism. It is assumed that the “extra” electron is coupled to the only intramolecular vibration, and a weak coupling to the dissipative subsystem (thermal bath) is taken into account. The vibronic energy levels and the wave functions of the isolated dimer (quantum part of the system) are num…

A new BEDT-TTF salt and polypyrrole films containing the chiral polyoxometalate [H4Co2Mo10O38]6−

Abstract The chiral polyoxometalate [H4Co2Mo10O38]6− has been used in the preparation of hybrid materials in the form of crystals or polymeric films. A new radical salt of the donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) containing the two enantiomers of this polyoxometalate has been obtained by electrocrystallization. This radical salt shows semiconducting behavior with room temperature conductivity of 9 S.cm−1 and activation energy of 40 meV. Polypyrrole films doped with a racemic mixture of polyoxometalates and also the enantiomerically pure (+)589-[H4Co2Mo10O38]6− have been prepared electrochemically. Circular dichroism experiments suggest that the chiral polyoxometalate…

The Use of Polyoxometalates in the Design of Layer‐Like Hybrid Salts Containing Cationic Mn 4 Single‐Molecule Magnets

Herein, we describe the combination of polyoxometalates (POMs) with a polynuclear metallic cluster Mn4 {Mn4 = [Mn4(OAc)2(pdmH)6]2+, (pdmH = deprotonated pyridine-2,6-dimethanol; C7H8NO2)} for the construction of ionic crystals with layered architectures. Choosing a POM with the appropriate charge and size not only allows for the fine tuning of the stacking periodicity, but it also allows modifying the in-plane packing motif and density of the cationic metallic clusters. The isolation of differently layered hybrid crystals with the same Mn4 single-molecule-magnet (SMM) system allowed for the direct comparison of the magnetic properties of such materials. The variation of the slow relaxation …

Exploiting Reaction-Diffusion Conditions to Trigger Pathway Complexity in the Growth of a MOF.

Coordination polymers (CPs), including metal–organic frameworks (MOFs), are crystalline materials with promising applications in electronics, magnetism, catalysis, and gas storage/separation. However, the mechanisms and pathways underlying their formation remain largely undisclosed. Herein, we demonstrate that diffusion-controlled mixing of reagents at the very early stages of the crystallization process (i.e., within ≈40 ms), achieved by using continuous-flow microfluidic devices, can be used to enable novel crystallization pathways of a prototypical spin-crossover MOF towards its thermodynamic product. In particular, two distinct and unprecedented nucleation-growth pathways were experimen…

Room-temperature electrical addressing of a bistable spin-crossover molecular system.

Polyoxometalate-Based Molecular Materials.

Molecule-based materials with active physical properties, in particular electrical, magnetic, and optical, are a focus of contemporary materials chemistry research. Certainly, one reason for this interest has been the realization that these materials can exhibit cooperative properties typically associated with the inorganic network solids, as for example metallic conduction or even superconductivity,1 ferromagnetism,2 and nonlinear optical properties.3 With respect to the electrical properties, many important achievements were obtained in the 1970s with the discovery of the first molecule-based metal in 1972,4 namely the π-electron donor-acceptor complex [TTF][TCNQ] (TTF ) tetrathiafulvalen…

Magnetic Molecular Conductors

Nitroxide Radicals as Templating Agents in the Synthesis of Magnets Based on Three-Dimensional Oxalato-Bridged Heterodimetallic Networks

Magnetic Properties of Ni II Cr III Layered Double Hydroxide Materials

This paper describes the isolation of four layered double hydroxide (LDH) compounds having the general formula[NiII3–xCrIIIx(OH)6](CO3)x/2·yH2O [x = 0.57 (1), 0.69 (2), 0.81 (3) and 0.93 (4)] by using homogeneous precipitation methods and varying the metal ratio in the synthetic solutions. All the reported compounds have carbonate anions in the interlamellar space. This fact forces the interlayer distances to remain unchanged in all the cases, thus providing an ideal system in which the changes observed in magnetic properties can be correlated with metal composition along the hydroxide layers.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Subphthalocyanines as narrow band red-light emitting materials

A series of new light emitting subphthalocyanines, lower homologues of phthalocyanines, were synthesized having color points covering the red-orange region of the visible spectrum. Additionally, they were found to be of potential use as narrow band emitters for red-light emitting diodes.

Near Isotropic D4d Spin Qubits as Nodes of a Gd(III)-Based Metal-Organic Framework

Embedding coherent spin motifs in reproducible molecular building blocks is a promising pathway for the realization of quantum technologies. Three-dimensional (3D) MOFs are a versatile platform for the rational design of extended structures employing coordination chemistry. Here, we report the synthesis and characterization of a gadolinium(III)-based MOF, [Gd(bipyNO)4](TfO)3·xMeOH (bipyNO = bipyridine,N,N′-dioxide; TfO = triflate; and MeOH = methanol) (quMOF-1), which presents a unique coordination geometry that leads to a tiny magnetic anisotropy (in terms of D, an equivalent zero-field splitting would be achieved by D = 0.006 cm–1) even compared with regular Gd(III) complexes. Pulsed elec…

Ferromagnetism and Chirality in Two-Dimensional Cyanide-Bridged Bimetallic Compounds

The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.

Ultra-broad spectral photo-response in FePS3 air-stable devices

Van der Waals materials with narrow energy gaps and efficient response over a broadband optical spectral range are key to widen the energy window of nanoscale optoelectronic devices. Here, we characterize FePS as an appealing narrow-gap p-type semiconductor with an efficient broadband photo-response, a high refractive index, and a remarkable resilience against air and light exposure. To enable fast prototyping, we provide a straightforward guideline to determine the thickness of few-layered FePS nanosheets extracted from the optical transmission characteristics of several flakes. The analysis of the electrical photo-response of FePS devices as a function of the excitation energy confirms a …

Synthesis, crystal structures and electronic properties of imidazoline nitroxide radicals bearing active groups in electropolymerisation

Thiophene-, phenylthiophene-, and indole-based nitronyl nitroxide (NN) and imino nitroxide (IN) radicals have been synthesised and their electrochemical and magnetic properties have been studied. Cyclic voltammetry measurements show that NN radicals (1–3) exhibit a one-electron quasi-reversible oxidation process that results in the formation of the corresponding nitrosonium cations. This behaviour pushes the oxidation potential of the other redox-active moiety to very high values. The oxidation of the thiophene subunit occurs at 2.35 V, whereas the oxidation of the phenylthiophene and indole moieties takes place at 1.65 and 1.39 V, respectively. Oxidation of IN radicals (4–5) is irreversibl…

Optimization of Polymer Blue-Light-Emitting Devices by Introducing a Hole-Injection Layer Doped with the Molecular Nanomagnet [Mn12O12(H2O)4(C6F5COO)16]

Isolated Mn-12 single-molecule magnets grafted on gold surfaces via electrostatic interactions

Electrostatic interactions drive the adsorption of polycationic single-molecule magnets onto anionic monolayers self-assembled on gold surfaces. Well-isolated magnetic clusters have been deposited and characterized using scanning tunneling microscopy and X-ray photoemission spectroscopy.

Insertion of a single-molecule magnet inside a ferromagnetic lattice based on a 3D bimetallic oxalate network: Towards molecular analogues of permanent magnets

The insertion of the single-molecule magnet (SMM) [MnIII(salen) (H2O)]2 2+ (salen2-=N,N-ethylenebis- (salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [MnIII(salen)(H2O)] 2[MnIICrIII(ox)3] 2×(CH3OH)×(CH3CN)2 (1). This cationic Mn2 cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn III(salen)(H2O)]2[ZnIICr III(ox)3]2×(CH3OH) ×(CH3CN)2 (2) and [InIII(sal 2-trien)][MnIICrIII(ox)3] ×(H2O)0.25×(CH3OH) 0.25×(CH3CN)0.25 (3), which are used as reference compounds. In 2 it has been shown that the magnetic isolatio…

Design of chiral magnets: Cyanide-bridged bimetallic assemblies based on cyclohexane-1,2-diamine

Abstract Four magnetic compounds based on chiral ligands trans-(1S,2S)-chxn and trans-(1R,2R)-chxn (chxn: cyclohexane-1,2-diamine), [Ni(trans-(1S,2S)-chxn)2]3[Fe(CN)6]2·2H2O (1), [Ni(trans-(1R,2R)-chxn)2]3[Fe(CN)6]2·2H2O (2), [Cu(trans-(1S,2S)-chxn)2]3[Fe(CN)6]2·4.5H2O (3) and [Cu(trans-(1R,2R)-chxn)2]3[Fe(CN)6]2·4.5H2O (4), are reported. The four compounds are chiral, as confirmed by X-ray analyses and circular dichroism measurements. From the magnetic point of view, 1 and 2 behave as ferromagnets, whereas 3 and 4 show a paramagnetic behavior.

Cover Feature: Fundamental Insights into the Covalent Silane Functionalization of NiFe Layered Double Hydroxides (Chem. Eur. J. 29/2020)

Molecular materials based upon organic π-donors and magnetic anions

Electrochemical combination of the magnetic dinuclear anion [MM'(C 2 O 4 )(NCS) 8 ] 4- (MM' = CrCr, CrFe) or paramagnetic mononuclear anion [Cr(NCS) 6 ] 3- with the ET organic π-donor (ET = BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) gives rise to two new series of molecular hybrid salts formulated (ET) 5 [MM'(C 2 O 4 )(NCS) 8 (MM' = CrCr (1), CrFe (2)), (ET) 8 [MM'(C 2 O 4 )(NCS) 8 ] (3), (ET) 5.5 f Cr(NCS) 6 ] (4) and (ET) 5 [(C 2 H 5 ) 4 N] [Cr(NCS) 6 ](THF) (5) (THF = tetrahydrofuran). The crystal structures consist of alternating organic and inorganic layers. The organic part does not produce any detectable effect on the magnetic properties coming from the inorganic sublattice. T…

An updated version of the computational package SIMPRE that uses the standard conventions for Stevens crystal field parameters

The crystal field approach used by SIMPRE is analyzed, verifying the exactness of the results concerning energy levels and magnetic properties calculated by the package. To coincide with the prevailing conventions, we reformulate the presentation of the crystal field parameters, so that the results are now, also from a formal point of view, strictly correct. New calculations are presented to test the influence of neglecting the excited J states, a common but critical approximation employed by SIMPRE. For that, we examine the case of Er(trensal) complex (H3 trensal = 2,2',2″-tris(salicylideneimino)triethylamine) where the influence of this approximation is found to be minimal. A patched vers…

ChemInform Abstract: Magnetic Exchange Between Metal Ions with Unquenched Orbital Angular Momenta: Basic Concepts and Relevance to Molecular Magnetism

This review article is a first attempt to give a systematic and comprehensive description (in the framework of the unified theoretical approach) of the exchange interactions in polynuclear systems based on orbitally degenerate metal ions in the context of their relevance to the modern molecular magnetism. Interest in these systems is related to the fundamental problems of magnetism and at the same time steered by a number of impressive potential applications of molecular magnets, like high-density memory storage units, nanoscale qubits, spintronics and photoswitchable devices. In the presence of orbital degeneracy, the conventional spin Hamiltonian (Heisenberg–Dirac–van Vleck model) becomes…

Polyoxometalates in Langmuir–Blodgett films: toward new magnetic materials

Abstract Polyoxometalates having various structures and properties can be organized by the Langmuir–Blodgett (LB) technique. The adsorption of such polyanions along a positively charged monolayer of DODA (dimethyldioctadecylammonium) induces large changes in the compression isotherm and enables the transfer of the Langmuir film onto solid substrate. X-ray diffraction and infrared dichroism experiments demonstrate that the polyoxometalates are organized in monolayers within the LB films. Furthermore, these magnetic multilayers were characterized by their paramagnetic susceptibility measured by a SQUID magnetometer.

High‐nuclearity mixed‐valence magnetic clusters : A general solution of the double exchange problem

We report here a general solution of the double‐exchange problem in the high‐nuclearity mixed valence systems containing arbitrary number P of the electrons delocalized over the network of N (P<N) localized spins. The developed approach is based on the successive (chainlike) spin‐coupling scheme and takes full advantage from the quantum angular momentum theory. In the framework of this approach the closed‐form analytical expressions are deduced for the matrix elements of the double exchange interaction, two‐electron transfer, and three‐center interaction that can be referred to as the potential exchange transfer. For the arbitrary nuclearity mixed‐valence systems the matrix elements of all …

Exchange transfer in high-nuclearity mixed valence magnetic clusters: Theoretical approach and expected manifestations

Abstract We report here a general solution of the exchange transfer problem in the high-nuclearity mixed valence clusters containing arbitrary number of itinerant electrons. The concept of two kinds of exchange transfer, namely kinetic and potential, is introduced by analogy with basic Anderson's mechanisms of the magnetic exchange. The kinetic exchange transfer is treated as a second order transfer process between two centres through the excited state of a third centre. The potential exchange transfer is also considered as a three-centre interaction but in this case only the ground states of the constituent ions are involved. The actual parameters of the exchange transfer are expected to b…

Insights on the coupling between vibronically active molecular vibrations and lattice phonons in molecular nanomagnets

Spin-lattice relaxation is a key open problem to understand the spin dynamics of single-molecule magnets and molecular spin qubits. While modelling the coupling between spin states and local vibrations allows to determine the more relevant molecular vibrations for spin relaxation, this is not sufficient to explain how energy is dissipated towards the thermal bath. Herein, we employ a simple and efficient model to examine the coupling of local vibrational modes with long-wavelength longitudinal and transverse phonons in the clock-like spin qubit [Ho(W$_5$O$_{18}$)$_2$]$^{9-}$. We find that in crystals of this polyoxometalate the vibrational mode previously found to be vibronically active at …

Synthesis and Characterization of a Soluble Bimetallic Oxalate-Based Bidimensional Magnet:  [K(18-crown-6)]3[Mn3(H2O)4{Cr(ox)3}3]

The "templating" K crown ether cation allows for the preparation of soluble layered oxalate-based bimetallic magnets, as in [K(18-crown-6]3{Mn3(H2O)4[Cr(ox)3]3}, with an unprecedented bidimensional polymeric anionic network that involves both oxalato bridges and H bonds. As in other 2D oxalate-bridged compounds, the compound behaves as a soft ferromagnet, with the onset of magnetic ordering occurring at 3.3 K.

Single-crystal EPR study of the bimetallic ferrimagnetic chain MnCu(EDTA)·6H2O

Abstract A single-crystal EPR study of the bimetallic chain compound MnCu(EDTA)·6H2O is reported. The angular dependence of the linewidth is discussed in relation to the magnetic dipole-dipole interaction, manganese zerofield splitting (ZFS) and copper hyperfine coupling. The calculation of the second moments indicates that ZFS is comparable to the dipolar contribution. The EPR data support the one-dimensional character of the compound.

Layered double hydroxide nanocomposites based on carbon nanoforms

Abstract Carbon nanoform (CNF)/layered double hydroxide (LDH) nanocomposites have been widely studied in recent years thanks to the combination of properties of both LDH and carbon nanomaterials. They exhibit improved or unexpected properties as a consequence of their hierarchical structures. There are three main reported approaches to prepare the nanocomposites: reassembly of nanocarbons and LDHs, direct formation of LDHs on nanocarbon materials, and the direct synthesis of nanocarbons on the LDH phase. The resulting CNF/LDH nanocomposites exhibit improved conductivity, mechanical properties, and redox reactivity; moreover, the hybridization confers hierarchical porosities and better dispe…

Solvent-Free Synthesis of a Pillared Three-Dimensional Coordination Polymer with Magnetic Ordering

A new magnetic coordination polymer, [Fe(bipy)(im)2] (bipy = 4,4-bipyridine and im = imidazole), has been synthesized in a solvent-free reaction. Structural analysis reveals a pillared 3D coordination polymer composed by neutral layers, formed by iron(II) and imidazolate linkers, interconnected by bipy ligands which serve as pillars. Magnetic measurements show that the material magnetically orders at low temperatures (Tc = 14.5 K) as a weak ferromagnet, likely due to a spin canting.

MVPACK: a package to calculate energy levels and magnetic properties of high nuclearity mixed valence clusters.

We present a FORTRAN code based on a new powerful and efficient computational approach to solve the double exchange problem for high-nuclearity MV clusters containing arbitrary number of localized spins and itinerant electrons. We also report some examples in order to show the possibilities of the program.

Organic/inorganic molecular conductors based upon perylene and Lindquist-type polyoxometalates

The preparation, structures and physical properties of the organic/inorganic radical salts based upon perylene (per) and Lindquist type polyoxometalates (POMs) are reported. Three new hybrid salts have been prepared: (per)5[Mo6O19] (1), (per)5[W6O19] (2), and (per)5[VW5O19] (3). Only structures 1 (P, Z = 2) and 3 (P, Z = 2) were fully determined as compound 2 was found to have unit cell parameters practically identical to 1 and, therefore, is considered isostructural with the latter. The structures consist of interpenetrated organic and mixed organic/inorganic layers in the ac plane alternating along the a direction. The organic layers present a novel packing mode of the perylene molecules …

Design of high-temperature f-block molecular nanomagnets through the control of vibration-induced spin relaxation

One of the main roadblocks that still hamper the practical use of molecular nanomagnets is their cryogenic working temperature. In the pursuit of rational strategies to design new molecular nanomagnets with increasing blocking temperature, ab initio methodologies play an important role by guiding synthetic efforts at the lab stage. Nevertheless, when evaluating vibration-induced spin relaxation, these methodologies are still far from being computationally fast enough to provide a useful predictive framework. Herein, we present an inexpensive first-principles method devoted to evaluating vibration-induced spin relaxation in molecular f-block single-ion magnets, with the important advantage o…

Hybrid Materials Based on Polyoxometalates with Solid State Properties

Molecular materials with cooperative physical properties constitute one of the most active focus of interest in contemporary materials science. An attractive chemical feature of these materials derives from the possibility of building them from molecular bricks using the advantages provided by molecular chemistry and the knowledge achieved over the last 20 years in the so-called molecular engineering. From the point of view of the physical properties, it is well known that molecular materials can exhibit the properties typically associated with the inorganic network solids, as for example metallic conductivity and superconductivity [1], ferromagnetism [2] and non-linear optics [3].

Confined growth of cyanide-based magnets in two dimensions

Herein we report the first hybrid magnetic material resulting from the intercalation of a cyanide-based molecular magnet into a solid-state layered host. More specifically, the use of a diamagnetic cationic Zn(II)-Al(lII) layered double hydroxide host allows for the formation of an anionic two-dimensional ferromagnetic Ni(II)-Cr(III) Prussian Blue analogue, from the templated assembly of its ionic molecular components in the confined interlamellar space offered by the inorganic host.

Preconcentration of emerging contaminants in environmental water samples by using silica supported Fe3O4 magnetic nanoparticles for improving mass detection in capillary liquid chromatography

A magnetic material based on Fe(3)O(4) magnetic nanoparticles incorporated in a silica matrix by using a sol-gel procedure has been used to extract and preconcentrate emerging contaminants such as acetylsalicylic acid, acetaminophen, diclofenac and ibuprofen from environmental water samples prior to the analysis with Capillary LC-MS. The use of the proposed silica supported Fe(3)O(4) magnetic nanoparticles enables surfactant free extracts for the analysis with MS detection without interferences in the ionisation step. Under the optimum conditions, we demonstrated the reusability of the magnetic sorbent material during 20 uses without loss in the extraction efficiency. In addition, no cleanu…

Coexistence of superconductivity and magnetism by chemical design.

Although the coexistence of superconductivity and ferromagnetism in one compound is rare, some examples of such materials are known to exist. Methods to physically prepare hybrid structures with both competing phases are also known, which rely on the nanofabrication of alternating conducting layers. Chemical methods of building up hybrid materials with organic molecules (superconducting layers) and metal complexes (magnetic layers) have provided examples of superconductivity with some magnetic properties, but not fully ordered. Now, we report a chemical design strategy that uses the self assembly in solution of macromolecular nanosheet building blocks to engineer the coexistence of supercon…

Ionically Assisted Charge Injection in Hybrid Organic−Inorganic Light-Emitting Diodes

We have developed hybrid organic−inorganic light-emitting diodes (HyLEDs) featuring a buffer layer of a conjugated polyelectrolyte (CPE) sandwiched between a light emitting polymer (LEP) film and a ZnO electron injection layer. Efficacies exceeding 5 cd/A and the possibility of employing various LEPs are demonstrated. These improvements, compared to HyLEDs without any interlayer, are attributed to the redistribution of ions in the CPE film, causing hole accumulation at the CPE/LEP interfaces and enhanced electron injection from the ZnO into the electroluminescent polymer. The intrinsic air-stability of the electrodes used in HyLEDs, together with the solution processability of the ZnO/CPE/L…

SIMPRE: A software package to calculate crystal field parameters, energy levels, and magnetic properties on mononuclear lanthanoid complexes based on charge distributions

This work presents a fortran77 code based on an effective electrostatic model of point charges around a rare earth ion. The program calculates the full set of crystal field parameters, energy levels spectrum, and wave functions, as well as the magnetic properties such as the magnetization, the temperature dependence of the magnetic susceptibility, and the Schottky contribution to the specific heat. It is designed for real systems that need not bear ideal symmetry and it is able to determine the easy axis of magnetization. Its systematic application to different coordination environments allows magneto-structural studies. The package has already been successfully applied to several mononucle…

Photomagnetic properties of an Fe(ii) spin-crossover complex of 6-(3,5-diamino-2,4,6-triazinyl)-2,2'-bipyridine and its insertion into 2D and 3D bimetallic oxalate-based networks.

International audience; The Fe(ii) complex of the L1 ligand (L1 = 6-(3,5-diamino-2,4,6-triazinyl)-2,2'-bipyridine) has been used as a templating cation for the growth of oxalate-based networks. The magnetic characterization of the [Fe(II)(L1)2](ClO4)2·CH3CN (1) precursor in the solid state has been performed for the first time showing that the low-spin (LS) state is predominating from 2 to 400 K with 10% of Fe(ii), which undergoes a gradual and irreversible spin-crossover above 350 K. 1 presents the LIESST effect with a photo-conversion close to 25% and a T(LIESST) of 49 K. During the preparation of 1, a secondary product of the formula [Fe(II)(L1)(CH3CN)2(H2O)](ClO4)2·CH3CN (2) has been ob…

Low Temperature Investigation of the Thermal and Magnetic Properties of 1-d Ferrimagnetic Systems

The series of structurally ordered bimetallic chains formulated as MM′ (EDTA).6H2O, in short (MM′), provides the most versatile known example of 1-dimensional ferrimagnets, since on the same structural support many different magnetic ions (Mn, Co, Ni and Cu(II)) can be selectively accommodated.1 Consequently, many choices of alternating magnetic moments with Heisenberg or Ising exchange couplings can be investigated. Moreover, taking into account that the M-M′ distances along the chain are alternating, this series could show at the same time an alternation of the exchange parameter2.

Tunable crossover between one- and three-dimensional magnetic dynamics inCoIIsingle-chain magnets organized by halogen bonding

Low-temperature magnetometry, ac susceptibility, and calorimetry have been employed to study Co-based single-chain magnets (SCMs) organized through halogen bonding. Magnetic hysteresis and maxima in the dc and ac susceptibilities, respectively, confirm the SCM behavior of the system. Several characteristic magnetic relaxation regimes are observed at different temperatures, which can be associated with both intra- and interchain exchange interactions. Remarkably, tweaking the rate at which an external magnetic field is swept along the axis of the chains enables a controlled transition between the one- and three-dimensional dynamics. Experiments on an isostructural Co-based SCM system crystal…

Single-crystal EPR spectroscopy of a Co(II) single-chain magnet

Abstract An electron paramagnetic resonance (EPR) study of a single crystal of Co II -based single-chain magnets (SCM) is presented. Discrete resonant absorptions are associated to the presence of magnetic domains within the chains of finite lengths determined by a competition between intra-chain exchange interactions and thermally excited single spin fluctuations. The results are interpreted as a transition from single spin dynamics at high temperature ( T  ∼20 K), associated to the Kramers doublet ground state of the individual Co II ions, to archetypical SCM dynamics at low temperatures, where intra-chain correlations form long magnetic domains, whose average length is imposed by the con…

ChemInform Abstract: High Nuclearity Magnetic Clusters: Magnetic Properties of a Nine Cobalt Cluster Encapsulated in a Polyoxometalate, (Co9(OH)3(H2O)6(HPO4) 2(PW9O34)3)16-.

Combination of magnetic susceptibility and electron paramagnetic resonance to monitor the 1D to 2D solid state transformation in flexible metal-organic frameworks of Co(II) and Zn(II) with 1,4-bis(triazol-1-ylmethyl)benzene.

Two families of coordination polymers, {[M(btix)(2)(OH(2))(2)]·2NO(3)·2H(2)O}(n) [M = Co (1), Zn (2), Co-Zn (3); btix = 1,4-bis(triazol-1-ylmethyl)benzene] and {[M(btix)(2)(NO(3))(2)]}(n) [M = Co (4), Zn (5), Co-Zn (6)], have been synthesized and characterized. The two conformations of the ligand, syn and anti, lead to one-dimensional (1D) cationic chains or two-dimensional (2D) neutral grids. Extrusion of the water molecules of the 1D compounds results in an irreversible transformation into the 2D compounds, which involves a change in conformation of the btix ligands and a rearrangement in the metal environment with cleavage and reformation of covalent bonds. This structural transformation…

Magneto-Optical Properties of Electrodeposited Thin Films of the Molecule-Based Magnet Cr5.5(CN)12·11.5H2O

Prof. E. Coronado , M. Makarewicz , J. P. Prieto-Ruiz , Dr. H. Prima-Garcia , Dr. F. M. Romero Instituto de Ciencia Molecular (ICMol) Universitat de Valencia C/Catedratico Jose Beltran, 2, 46980-Paterna, Spain E-mail: eugenio.coronado@uv.es; helena.prima@uv.es; fmrm@uv.es

Deciphering the Role of Dipolar Interactions in Magnetic Layered Double Hydroxides

Layered double hydroxides (LDHs) exhibit unparalleled anion exchange properties and the ability to be exfoliated into 2D nanosheets, which can be used as a building block to fabricate a wide variety of hybrid functional nanostructured materials. Still, if one wants to use LDHs as a magnetic building blocks in the design of complex architectures, the role played by the dipolar magnetic interactions in these layered materials needs to be understood. In this work, we synthesized and characterized a five-membered CoAl-LDH series with basal spacing ranging from 7.5 to 34 Å. A detailed experimental characterization allows us to conclude that the main factor governing the dipolar interactions betw…

Pseudo-Jahn–Teller Origin of the Metastable States in Sodium Nitroprusside

Abstract A new model for the photochromic effect in sodium nitroprusside Na 2 [Fe(CN) 5 (NO)]·2H 2 O based on the concept of the pseudo-Jahn–Teller effect is proposed. The model takes into account the electron transfer from the Fe 2+ ion to the π ∗ orbitals of the NO-ligand as well as the vibronic mixing of three electronic states of the Fe–NO fragment through the non-symmetric and full symmetric modes. The problem is solved within the adiabatic approximation. Under certain conditions, the lower sheet of the adiabatic potential is shown to possess three minima with the increasing energies that correspond to the N-bound, sideways bound, and O-bound NO group. The barriers between the minima a…

Hybrid Molecular Materials Based upon Organic π-Electron Donors and Metal Complexes. Radical Salts of Bis(ethylenethia)tetrathiafulvalene (BET-TTF) with the Octahedral Anions Hexacyanoferrate(III) and Nitroprusside. The First Kappa Phase in the BET-TTF Family

The synthesis, structure, and physical characterization of two new radical salts formed with the organic donor bis(ethylenethia)tetrathiafulvalene (BET-TTF) and the octahedral anions hexacyanoferrate(III), [Fe(CN)(6)](3-), and nitroprusside, [Fe(CN)(5)NO](2-), are reported. These salts are (BET-TTF)(4)(NEt(4))(2)[Fe(CN)(6)] (1) (monoclinic space group C2/c with a = 38.867(7) A, b = 8.438(8) A, c = 11.239(6) A, beta = 90.994(9) degrees, V = 3685(4) A(3), Z = 4) and (BET-TTF)(2)[Fe(CN)(5)NO].CH(2)Cl(2) (2) (monoclinic space group C2/c with a = 16.237(6) A, b = 18.097(8) A, c = 12.663(7) A, beta = 106.016(9) degrees, V = 3576(3) A(3), Z = 4). In salt 1 the organic BET-TTF molecules are packed …

Beyond the spin model: exchange coupling in molecular magnets with unquenched orbital angular momenta.

In this critical review we review the problem of exchange interactions in polynuclear metal complexes involving orbitally degenerate metal ions. The key feature of these systems is that, in general, they carry an unquenched orbital angular momentum that manifests itself in all their magnetic properties. Thus, interest in degenerate systems involves fundamental problems related to basic models in magnetism. In particular, the conventional Heisenberg-Dirac-Van Vleck model becomes inapplicable even as an approximation. In the first part we attempt to answer two key questions, namely which theoretical tools are to be used in the case of degeneracy, and how these tools can be employed. We demons…

Correction: Effect of nanostructuration on the spin crossover transition in crystalline ultrathin films

Correction for ‘Effect of nanostructuration on the spin crossover transition in crystalline ultrathin films’ by Víctor Rubio-Giménez et al., Chem. Sci., 2019, DOI: 10.1039/c8sc04935a.

Isostructural compartmentalized spin-crossover coordination polymers for gas confinement

[EN] Here we present two FeII coordination polymers that possess discrete compartments suitable for CO2 physisorption despite the lack of permanent channels. The two crystalline materials, of general formula [Fe(btzbp)3](X)2 (X = ClO4 or BF4), present voids of ca. 250 Å3, which each can accommodate up to two CO2 molecules. The abrupt spin transition can be modified upon CO2 sorption, and different magnetic behaviour is observed depending on the number of molecules sorbed.

Publisher's Note: “Attosecond state-resolved carrier motion in quantum materials probed by soft x-ray XANES” [Appl. Phys Rev. 8, 011408 (2021)]

Recent developments in attosecond technology led to table-top x-ray spectroscopy in the soft x-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real-time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, and TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near-edge spectroscopy to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the ele…

High-nuclearity magnetic clusters: Magnetic interactions in clusters encapsulated by molecular metal oxides

Abstract The ability of the molecular metal oxides derived from the Keggin anion [PW 12 O 40 ] 3− to accommodate magnetic ions at specific sites, giving rise to polymetallic clusters with increasing spin nuclearities is discussed. Examples of magnetic clusters with three, four and nine metal ions exhibiting ferromagnetic exchange couplings or a coexistence of ferro- and antiferromagnetic couplings are reported.

Intercalation of cobalt(II)-tetraphenylporphine tetrasulfonate complex in magnetic NiFe-layered double hydroxide

Abstract Hybrid magnetic multilayers have been synthesized by means of intercalation of [5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato]cobalt(II) (CoTPPS) complex in the interlayer space of a Ni II Fe III layered double hydroxide (LDH), through anion-exchange reaction. A sebacate ( − OOC–(CH 2 ) 8 –COO − ) intercalated NiFe-LDH have been used as precursor, facilitating the anion exchange reaction, thus permitting the inclusion of a paramagnetic macrocycle inside the ferrimagnetic NiFe-LDH layers. The material has been characterized by XRD, FT-IR, SEM, SQUID and ESR. The T c for the hybrid NiFe–CoTPPS, ca. 11–12 K, is very close to that shown by the precursor, despite that the intercala…

First tetrathiafulvalene (TTF) cation-radical salt containing the inorganic polyoxometalate β-[Mo8O26]4⊖

Scanning tunnelling spectroscopy study of paramagnetic superconducting β''-ET(4)[(H(3)O)Fe(C(2)O(4))(3)]·C(6)H(5)Br crystals.

Scanning tunnelling spectroscopy (STS) and microscopy (STM) were performed on the paramagnetic molecular superconductor β''-ET(4)[(H(3)O)Fe(C(2)O(4))(3)]·C(6)H(5)Br. Under ambient pressure, this compound is located near the boundary separating superconducting and insulating phases of the phase diagram. In spite of a strongly reduced critical temperature T(c) (T(c) = 4.0 K at the onset, zero resistance at T(c) = 0.5 K), the low temperature STS spectra taken in the superconducting regions show strong similarities with the higher T(c) ET κ-derivatives series. We exploited different models for the density of states (DOS), with conventional and unconventional order parameters to take into accoun…

Bimetallic cyanide-bridged complexes based on the photochromic nitroprusside anion and paramagnetic metal complexes

Abstract Three novel compounds formed by the photochromic nitroprusside anion, [Fe(CN)5NO]2−, and the paramagnetic complexes [Cu(C19H18N6)]2+, [Ni(C6H14N2)2]2+ and [Ni(cyclam)]2+ are reported. The structure of [Cu(C19H18N6)][Fe(CN)5NO] (1) comprises binuclear complexes with a [Fe(CN)5NO]2− anion linked to a [Cu(C19H18N6)]2+ cation. The structure of [Ni(C6H14N2)2][Fe(CN)5NO]·6.5H2O (2) and [Ni(cyclam)][Fe(CN)5NO]·4H2O (3) consists of zigzag chains formed by an alternate array of the paramagnetic cations and [Fe(CN)5NO]2− anions. The three compounds are paramagnets; a fourth compound containing [cis-Ni(en)2]2+ cations and [Fe(CN)5NO]− anions does not show a change in the magnetic properties a…

Probing the spin dimensionality in single-layer CrSBr van der Waals heterostructures by magneto-transport measurements

Two-dimensional (2D) magnetic materials offer unprecedented opportunities for fundamental physics and applied research in spintronics and magnonics. Beyond the pioneering studies on 2D CrI3 and Cr2Ge2Te6, this emerging field has expanded to 2D antiferromagnets exhibiting different spin anisotropies and textures. Of particular interest is the layered metamagnet CrSBr, a relatively air-stable semiconductor formed by antiferromagnetically-coupled ferromagnetic layers (Tc~150 K) that can be exfoliated down to the single-layer. It presents a complex magnetic behavior with a dynamic magnetic crossover leading to a low-temperature hidden order below T*~40 K. Here, we inspect the magneto-transport …

Synthesis and characterisation of polymeric metal-ion carboxylates from benzene-1,3,5-tricarboxylic acid with Mn(II), Co(II) or Zn(II) and 2,2-bipyridyl, phenanthroline or a pyridyl-2-(1-methyl-1H-pyrazol-3-yl) derivative

A total of 13 new co-ordination solids have been prepared of composition [Co(HBTC)(PHEN)(H2O)] (12), [Mn-3(BTC)(2)(PHEN)(3)] (13), [Mn(HBTC)(6)(H2O)] (14), [Mn(HBTC)(7)(H2O)] (15), [Zn-3(BTC)(2)(6)(3)(H2O)(3)]. 4H(2)O (16), [Zn-(HBTC)(6)(H2O)] (17), [Zn(H2BTC)(2)(6)] (18), [Zn(HBTC)(7)(H2O)] (19), [Zn(HBTC)(8)(H2O)] (20), [Zn-2(HBTC)(2)(9)(2)]. 2H(2)O (21), [Zn(HBTC)(10)(H2O)].H2O (22), [Co(HBTC)(10)(H2O)].H2O (23) and [Co(HBTC)(11)(H2O)] (24) 6 = pyridine-2-(1-methyl-1H-pyrazol-3-yl); 7 = pyridine-2-(1-methyl-4-bromo-1H-pyrazol-3-yl); 8 = pyridine-2-(1-methyl-4-nitro-1H-pyrazol-3-yl); 9 = pyridine-2-(1-methyl-5-trifluoromethyl-1H-pyrazol-3-yl); 10 = pyridine-2-(1-methyl-5-tert-butyl-1H-pyr…

Quantum coherent spin-electric control in a molecular nanomagnet at clock transitions

Electrical control of spins at the nanoscale offers significant architectural advantages in spintronics, because electric fields can be confined over shorter length scales than magnetic fields1–5. Thus, recent demonstrations of electric-field sensitivities in molecular spin materials6–8 are tantalizing, raising the viability of the quantum analogues of macroscopic magneto-electric devices9–15. However, the electric-field sensitivities reported so far are rather weak, prompting the question of how to design molecules with stronger spin–electric couplings. Here we show that one path is to identify an energy scale in the spin spectrum that is associated with a structural degree of freedom with…

2D magnetic MOFs with micron-lateral size by liquid exfoliation

The isolation in large amounts of high-quality flakes of 2D MOFs remains a challenge. In this work, we develop a liquid exfoliation procedure to obtain nanosheets for a whole family of Fe-based magnetic MOFs, MUV-1-X. High-quality crystalline layers with lateral sizes of 8 µm and thicknesses of 4 nm, which keep the structural integrity and magnetic properties, are obtained.

Coherent manipulation of three-qubit states in a molecular single-ion magnet

We study the quantum spin dynamics of nearly isotropic Gd3+ ions entrapped in polyoxometalate molecules and diluted in crystals of a diamagnetic Y3+ derivative. The full energy-level spectrum and the orientations of the magnetic anisotropy axes have been determined by means of continuous-wave electron paramagnetic resonance experiments, using X-band (9-10 GHz) cavities and on-chip superconducting waveguides and 1.5-GHz resonators. The results show that seven allowed transitions between the 2S+1 spin states can be separately addressed. Spin coherence T2 and spin-lattice relaxation T1 rates have been measured for each of these transitions in properly oriented single crystals. The results sugg…

Ultrafast Coherent THz Lattice Dynamics Coupled to Spins in the van der Waals Antiferromagnet FePS3

Coherent THz optical lattice and hybridized phonon–magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS3. The laser-driven lattice and spin dynamics are investigated in a bulk crystal as well as in a 380 nm-thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump-probe magneto-optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2 THz decreases as the sample is heated up to the Néel temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long-ra…

Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound

Crystal engineering--the planning and construction of crystalline supramolecular architectures from modular building blocks--permits the rational design of functional molecular materials that exhibit technologically useful behaviour such as conductivity and superconductivity, ferromagnetism and nonlinear optical properties. Because the presence of two cooperative properties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of molecular materials with two properties that are difficult or impossible to combine in a conventional inorganic solid with a continuous lattice. A promising strategy for creating this…

Force-free state in a superconducting single crystal and angle-dependent vortex helical instability

Superconducting 2H-NbSe2 single crystals show intrinsic low pinning values. Therefore, they are ideal materials with which to explore fundamental properties of vortices. (V, I) characteristics are the experimental data we have used to investigate the dissipation mechanisms in a rectangular shape 2H-NbSe2 single crystal. Particularly, we have studied dissipation behavior with magnetic fields applied in the plane of the crystal and parallel to the injected currents, i.e. in the force-free state where the vortex helical instability governs the vortex dynamics. In this regime, the data follow the elliptic critical state model and the voltage dissipation shows an exponential dependence.Moreover,…

Self-Assembly of 1D/2D Hybrid Nanostructures Consisting of a Cd(II) Coordination Polymer and NiAl-Layered Double Hydroxides

The preparation and characterization of a novel hybrid material based on the combination of a 2D-layered double hydroxide (LDH) nanosheets and a 1D-coordination polymer (1D-CP) has been achieved through a simple mixture of suspensions of both building blocks via an exfoliation/restacking approach. The hybrid material has been thoroughly characterized demonstrating that the 1D-CP moieties are intercalated as well as adsorbed on the surface of the LDH, giving rise to a layered assembly with the coexistence of the functionalities of their initial constituents. This hybrid represents the first example of the assembly of 1D/2D nanomaterials combining LDH with CP and opens the door for a plethora…

White-light phosphorescence emission from a single molecule: application to OLED.

A simple mononuclear cyclometallated iridium(III) complex exhibits white photo- and electro- luminescence in the wavelength range from 440 to 800 nm, which originates from a single emitting excited state of mixed character. Bolink Henk, Henk.Bolink@uv.es ; Coronado Miralles, Eugenio, Eugenio.Coronado@uv.es

Large Magnetic Polyoxometalates Containing the Cobalt Cubane ‘[CoIIICo3II(OH)3(H2O)6–m(PW9O34)]3− (m = 3 or 5) as a Subunit

A synthetic procedure is presented to construct new magnetic polyoxometalates (POMs) containing one or two subunits of ‘[CoIIICo3II(OH)3(H2O)6−m(PW9O34)]3−' (m = 3 or 5). The substitution of the water ligands present in these subunits by oxo or hydroxo ligands belonging to other POM fragments, gives rise to four, larger POM anions: [Co7(OH)6(H2O)6(PW9O34)2]9− (2), [Co7(OH)6(H2O)4(PW9O34)2]n9n- (2′), [Co11(OH)5(H2O)5(W6O24)(PW9O34)3]22− (3) and [{Co4(OH)3(H2O)(PW9O34)}2{K⊂(H2W12O41)2}{Co(H2O)4}2]17− (4). The crystal structures, magnetic characterization and stabilities in aqueous solutions of these POM derivatives are also presented.

Radical cation salts based on BEDT-TTF and the paramagnetic anion [Cr(NCS)6]3−

Abstract A new radical cation salt formulated as (ET)5.5[Cr(NCS)6] (ET = BEDT-TTF = bis(ethylene)dithiotetrathiafulvalene) has been synthesised and characterised by X-ray diffraction and magnetic measurements. The structure shows the presence of alternating layers of the ET units and mixed layers of anions and an isolated ET molecule. The magnetic susceptibility data in the temperature range 2–300 K show a Curie law with C = 1.771 cm3.K.mol−1 and Nα = 1.20.10−5 cm3.mol−1, in agreement with the presence of isolated Cr(III) without any contribution from the organic part.

Hybrid Interfaces in Molecular Spintronics

Molecular/inorganic multilayer heterostructures are gaining attention in molecular electronics and more recently in new generation spintronic devices. The intrinsic properties of molecular materials as low cost, tuneability, or long spin lifetimes were the original reasons behind their implementation. However, the non-innocent role played by these hybrid interfaces is a determinant factor in the device performance. In this account we will give an overview about different types of hybrid molecular system/ferromagnet interfaces, which can be of direct application in molecular spintronics. This includes the insertion of a 2D material in between the molecular system and the ferromagnet. As pers…

Attosecond state-resolved carrier motion in quantum materials probed by soft x-ray XANES

Recent developments in attosecond technology led to tabletop X-ray spectroscopy in the soft X-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near edge spectroscopy (XANES) to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the …

Path to Overcome Material and Fundamental Obstacles in Spin Valves Based on Mo S 2 and Other Transition-Metal Dichalcogenides

International audience; Experimental studies on spin valves with exfoliated 2D materials face the main technological issue of ferromagnetic electrode oxidation during the 2Ds integration process. As a twofold outcome, magne-toresistance (MR) signals are very difficult to obtain and, when they finally are, they are often far from expectations. We propose a fabrication method to circumvent this key issue for 2D-based spintronics devices. We report on the fabrication of NiFe/MoS 2 /Co spin valves with mechanically exfoliated mul-tilayer MoS 2 using an in situ fabrication protocol that allows high-quality nonoxidized interfaces to be maintained between the ferromagnetic electrodes and the 2D la…

A general approach for the calculation of the energy levels and the inelastic neutron scattering cross-section of highly nuclear magnetic clusters

Abstract We develop here a general approach to calculate in an efficient way the spin levels as well as the spin eigenfunctions and the INS intensities of clusters formed by large numbers of exchange-coupled magnetic metal ions. The approach is based on the successive use of the irreducible tensor operator techniques and takes into account all kinds of magnetic exchange interactions between the metal ions. The potentialities of this approach are illustrated from an example comprising nine exchange-coupled Ni (II) ions.

VIBPACK: A package to treat multidimensional electron-vibrational molecular problems with application to magnetic and optical properties

We present a FORTRAN code based on a new powerful and efficient computational approach to solve multidimensional dynamic Jahn-Teller and pseudo Jahn-Teller problems. This symmetry-assisted approach constituting a theoretical core of the program is based on the full exploration of the point symmetry of the electronic and vibrational states. We also report some selected examples of increasing complexity aimed to display the theoretical background as well as the advantages and capabilities of the program to evaluate of the energy pattern, magnetic and optical properties of large multimode vibronic systems. © 2018 Wiley Periodicals, Inc.

Electrical sensing of the thermal and light induced spin transition in robust contactless spin-crossover/graphene hybrid devices

Hybrid devices based on spin-crossover (SCO)/2D heterostructures grant a highly sensitive platform to detect the spin transition in the molecular SCO component and tune the properties of the 2D material. However, the fragility of the SCO materials upon thermal treatment, light irradiation or contact with surfaces and the methodologies used for their processing have limited their applicability. Here, we report an easily processable and robust SCO/2D hybrid device with outstanding performance based on the sublimable SCO [Fe(Pyrz)2] molecule deposited over CVD-graphene, which is fully compatible with electronics industry protocols. Thus, a novel methodology based on growing an elusive polymorp…

Ab initio calculations of the transfer parameters and coulombic repulsion and estimation of their effects on the electron delocalization and magnetic coupling in mixed-valence Keggin polyoxotungstates

International audience; In this work, we present ab initio calculations on embedded fragments that permit to extract the value of the effective electron transfer integral and coulombic repulsion between W nearest neighbour atoms in a mixed-valence αPW12O40 Keggin polyoxoanion. This allows us to perform a quantitative study of the influence of these two parameters on the magnetic properties of Keggin polyoxoanions reduced by two electrons. We surprisingly find that the electron transfer between edge-sharing and corner-sharing WO6 octahedra have very close values, and show that the punctual charges estimation of coulombic repulsion may not be accurate enough to study the electronic distributi…

van der Waals heterostructures based on atomically-thin superconductors

Van der Waals heterostructures (vdWHs) allow the assembly of high-crystalline two-dimensional (2D) materials in order to explore dimensionality effects in strongly correlated systems and the emergence of potential new physical scenarios. In this work, it is illustrated the feasibility to integrate 2D materials in-between 2D superconductors. Particularly, it is presented the fabrication and electrical characterization of vertical vdWHs based on air-unstable atomically-thin transition metal dichalcogenides formed by NbSe2/TaS2/NbSe2 stacks, with TaS2 being the insulator 1T-TaS2 or the metal 2H-TaS2. Phase transitions as 1T-TaS2 charge density wave and NbSe2 superconductivity are detected. An …

Localization vs. Delocalization in Molecules and Clusters: Electronic and Vibronic Interactions in Mixed Valence Systems

The interplay between electron delocalization and magnetic interactions play a key role in areas as diverse as solid state chemistry (bulk magnetic materials, superconductors,...) [1] and biology (iron-sulfur proteins, manganese-oxo clusters ...) [2]. In molecular inorganic chemistry these two electronic processes have been traditionally studied independently. Thus, the electron dynamics has been extensively investigated in mixedvalence dimers [3] as exemplified by the Creutz-Taube complex [(NH3)5RuII(pyrazine)RuIII(NH3)5]. In this kind of molecular complexes one extra electron is delocalized over two diamagnetic metal sites. Therefore, they constitute model systems for the study of the ele…

Chemical Design and Magnetic Ordering in Thin Layers of 2D Metal–Organic Frameworks (MOFs)

Through rational chemical design, and thanks to the hybrid nature of metal&minus;organic frameworks (MOFs), it is possible to prepare molecule-based 2D magnetic materials stable at ambient conditions. Here, we illustrate the versatility of this approach by changing both the metallic nodes and the ligands in a family of layered MOFs that allows the tuning of their magnetic properties. Specifically, the reaction of benzimidazole-type ligands with different metal centers (MII = Fe, Co, Mn, Zn) in a solventfree synthesis produces a family of crystalline materials, denoted as MUV-1(M), which order antiferromagnetically with critical temperatures that depend on M. Furthermore, the incorporation o…

Single chain magnets based on the oxalate ligand.

The anionic oxalate-bridged bimetallic chain [Co(H2O)2Cr(ox)3]- shows slow relaxation of the magnetization, typical of the so-called single-chain magnets, when crystallized in segregated layers in a mixed salt with the supramolecular cations [C12H24O6K]+ and [(C12H24O6)(FC6H4NH3)]+. This is the first time that such phenomenon has been observed in an oxalate-bridge material. In view of the wide synthetic versatility exhibited by the oxalate ligand, it opens the door for the realization of a complete family of SCM materials whose physical properties might be tuned by the suitable replacement of M3+ ions within the chain. The information extracted from the systematic study of these compounds s…

Unusual packing of ET molecules caused by π–π stacking interactions with TRISPHAT molecules in two [ET][TRISPHAT] salts (ET=bis(ethylenedithio)tetrathiafulvalene, TRISPHAT=(tris(tetrachlorobenzenediolato)phosphate(V)))

Abstract The synthesis, structure and physical properties of two new radical salts formed with the organic donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) and a racemic mixture of the chiral anion (tris(tetrachlorobenzenediolato)phosphate(V)) (TRISPHAT) are reported. The structure of the salts (ET)4[TRISPHAT]4 · 3.5H2O (1) and (ET)(TRISPHAT) · CH2Cl2 · CH3CN (2) has been solved by X-ray single crystal diffraction. Unusual packings of ET molecules are obtained in the two structures. The electrical properties indicate that both compounds are insulators. This is in agreement with the isolation of the ET molecules and their complete ionization. On the other hand, the anisotropy of …

Organized assemblies of magnetic clusters

Abstract In this work we have explored the possibilities to create layered organizations of the Mn 12 single-molecule magnets using the Langmuir–Blodgett technique or attaching these clusters onto a metal surface by preparing self-assembled monolayers (SAMs). In the first part we discuss the use of the Langmuir–Blodgett (LB) technique in order to obtain organized magnetic films formed by monolayers of these clusters. Two strategies have been used with this aim. The first one consists of mixing Mn 12 acetate or benzoate derivatives with an amphiphile, while the second procedure is based on the use of Mn 12 derivatives specifically designed to form LB films. An alternative method is that of p…

Permanent magnetism in apoferritin-encapsulated Pd nanoparticles

Pd nanoparticles have been prepared within the apoferritin cavity. X-Ray powder diffraction, transmission electronic microscopy and magnetization measurements have been used for characterizing the nanoparticles. The nanoparticles exhibit permanent magnetism at room temperature.

Structural re-arrangement in two hexanuclear CuIIcomplexes: from a spin frustrated trigonal prism to a strongly coupled antiferromagnetic soluble ring complex with a porous tubular structure

The addition of water to a chloroform solution of the Cu6 trigonal prism complex [Cu6(μ6F)(μ2OH)(μ3OCH3)2(μ2OCH3)2(3,5-Me2pz)6] (1) (3,5-Me2pz− = 3,5-dimethylpyrazolate) results in the formation of the Cu6 planar hexagonal ring complex [Cu6(μ2OH)6(3,5-Me2pz)6]·CH3CN·CHCl3 (2). A simple mechanism for this structural re-arrangement is proposed, in which 2 can be viewed as a hydrolysis product of 1. This process is clearly noticeable in the magnetic properties, which change from spin frustrated with a weak antiferromagnetic coupling in 1, to strongly antiferromagnetic in 2. Interestingly, the hexagonal ring complex 2 self-assembles in the solid state to form a porous hexagonal tubular structur…

Chiral Molecular Magnets: Synthesis, Structure, and Magnetic Behavior of the Series [M(L-tart)] (M = MnII, FeII, CoII, NiII;L-tart = (2R,3R)-(+)-tartrate)

A new series of layered magnets with the formula [M(L-tartrate)] (M = Mn(II), Co(II), Fe(II), Ni(II); L-tartrate = (2R,3R)-(+)-tartrate) has been prepared. All of these compounds are isostructural and crystallize in the chiral orthorhombic space group I222, as found by X-ray structure analysis. Their structure consists of a three-dimensional polymeric network in which each metal shows distorted octahedral coordination bound to four L-tartrate ligands, two of which chelate through an alcohol and a carboxylate group and the other two bind terminally through a monodentate carboxylate group. The chirality of the ligand imposes a Delta conformation on all metal centers. Magnetically, the paramag…

Hybrid materials containing organometallic cations and 3-D anionic metal dicyanamide networks of type [Cp*2M][M′(dca)3]

A new series of hybrid materials of type [Cp*2M][M′(dca)3] has been prepared by cation templation and structurally characterised (M = Fe(III), Co(III); M′ = Mn(II), Fe(II), Co(II), Ni(II), Cd(II); dca− = N(CN)2−). The crystallographic analysis of [Cp*2Fe][Cd(dca)3] showed that the [Cd(dca)3]− anionic framework is of a symmetrical 3-D α-polonium type, containing octahedral Cd nodes and μ1,5-dca bridging ligands. The [Cp*2Fe]+ cations occupy the cube-like cavities within the framework. The cationic and anionic-framework sublattices remain magnetically independent and display susceptibilities, over the range 300 to 2 K, of a Curie–Weiss nature obtained by adding a S = 1/2 (Cp*2Fe+) or a S = 0 …

Confined growth of carbon nanoforms in one-dimension by fusion of anthracene rings inside the pores of MCM-41

We report a simple two-step procedure that uses anthracene, a cheap polyaromatic hydrocarbon with low melting point, as a molecular precursor to produce carbon nanoforms (CNFs). First, we describe the chemical synthesis of graphite from the fusion of anthracene rings at relatively low temperature (520 °C) followed by cyclodehydrogenation. Next, we extend this protocol to the synthesis of CNFs by confining the molecular precursor in a mesoporous host like MCM-41. The confined environment favors one-dimensional growth of CNFs with sizes controlled by the pores of the mesoporous host.

Electron Delocalization and Electrostatic Repulsion at the Origin of the Strong Spin Coupling in Mixed-Valence Keggin Polyoxometalates: Ab Initio Calculations of the One- and Two-Electron Processes

International audience; Cet article détaille une procédure générale qui associe l′évaluation de paramètres microscopiques et la prédiction de propriétés macroscopiques. Les principales interactions entre les électrons délocalisés sur des polyoxométalates à valence mixte sont extraites à partir du calcul de la spectroscopie de valence de fragments immergés dans un bain qui reproduit les principaux effets du reste du cristal sur le fragment considéré. Nous avons extrait non seulement la valeur du transfert électronique, du couplage magnétique et du paramètre de "exchange-transfer" entre ions métalliques premiers et seconds voisins, mais encore la valeur de la répulsion électrostatique entre l…

Highly phosphorescent perfect green emitting iridium(iii) complex for application in OLEDs.

A novel iridium complex, [bis-(2-phenylpyridine)(2-carboxy-4-dimethylaminopyridine)iridium(III)] (N984), was synthesized and characterized using spectroscopic and electrochemical methods; a solution processable OLED device incorporating the N984 complex displays electroluminescence spectra with a narrow bandwidth of 70 nm at half of its intensity, with colour coordinates of x = 0.322; y = 0.529 that are very close to those suggested by the PAL standard for a green emitter. Bolink, Henk, Henk.Bolink@uv.es ; Coronado Miralles, Eugenio, Eugenio.Coronado@uv.es ; Garcia Santamaria, Sonsoles Amor, Sonsoles.Garcia@uv.es

Magnetic Polyoxometalates:  Anisotropic Antiferro- and Ferromagnetic Exchange Interactions in the Pentameric Cobalt(II) Cluster [Co3W(D2O)2(CoW9O34)2]12-. A Magnetic and Inelastic Neutron Scattering Study

The ground-state properties of the pentameric Co(II) cluster [Co(3)W(D(2)O)(2)(CoW(9)O(34))(2)](12-) were investigated by combining magnetic susceptibility and low-temperature magnetization measurements with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na(12)[Co(3)W(D(2)O)(2)(CoW(9)O(34))(2)].46D(2)O. The encapsulated magnetic Co(5) unit consists of three octahedral and two tetrahedral oxo-coordinated Co(II) ions. Thus, two different types of exchange interactions are present within this cluster: a ferromagnetic interaction between the octahedral Co(II) ions and an antiferromagnetic interaction between the octahedral and the tetrahedral…

A stable oxoverdazyl free radical: Structural and magnetic characterization

Abstract The structure and magnetic properties (susceptibility and ESR) of the stable oxoverdazyl free radical 6-(4-acetamidophenyl)-1,4,5,6-tetrahydro-2,4-dimethyl-1,2,4,5-tetrazin-3(2H)-one are presented. The crystal structure consists of chains of parallel planar molecules running along the b-axis. These chains are formed by dimers with a ring-over-bond overlap and a significant offset between dimers, although with similar inter- and intradimer distances. The susceptibility measurements show that this compound is an S = 1/2 paramagnet with weak antiferromagnetic interactions. The magnetic susceptibility can be very well reproduced with an antiferromagnetic regular chain model with g = 2.…

A quantum spin liquid candidate isolated in a two-dimensional CoIIRhIII bimetallic oxalate network

A quantum spin liquid (QSL) is an elusive state of matter characterized by the absence of long-range magnetic order, even at zero temperature, and by the presence of exotic quasiparticle excitations. In spite of their relevance for quantum communication, topological quantum computation and the understanding of strongly correlated systems, like high-temperature superconductors, the unequivocal experimental identification of materials behaving as QSLs remains challenging. Here, we present a novel 2D heterometallic oxalate complex formed by high-spin Co(II) ions alternating with diamagnetic Rh(III) in a honeycomb lattice. This complex meets the key requirements to become a QSL: a spin ½ ground…

Influence of the covalent grafting of organic radicals to graphene on its magnetoresistance

Graphene was obtained by direct exfoliation of graphite in o-dichlorobenzene (oDCB) or benzylamine, and further functionalized with 4,4′-[(1,3-dioxo-1,3-propanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl-1-piperidinyloxy] (1-TEMPO) organic radicals by using the Bingel–Hirsch cyclopropanation reaction. Here, the use of different solvents permits variation of the density of radicals anchored to the carbon layers. Covalent grafting is unambiguously demonstrated by TGA, μ-Raman, XPS and EPR measurements, which also rule out spurious physisorption. Our transport measurements indicate that the conduction mechanism varies as a function of the density of radicals grafted to the carbon layers. Moreover, t…

Nanoscale Deposition of Single-Molecule Magnets onto SiO2 Patterns

bet on a silicon oxide template while the rest ofthe macroscopic surface remains free of molecules. Local oxi-dation was used to fabricate silicon oxide nanopatterns, eitherdots or stripes, over a Si (100) surface coated with a SAM.Their width ranged from 30 to 500 nm whereas the lengthcould be modified from a few nanometers up to several mi-crometers. Nanoscale direct assembly arose from a combina-tion of three factors: i) the strength of the attractive electro-static interactions between the molecules and the local oxides;ii) the weak repulsive interaction between the molecules andthe unpatternedsurface; and iii) the size of the nanopattern.Local oxidation nanolithography (LON) allows the…

Localisation vs. delocalisation in the dimeric mixed-valence clusters in the generalised vibronic model. Magnetic manifestations

Abstract The problem of localisation–delocalisation in the dimeric mixed-valence clusters is considered in the framework of the generalised vibronic model. The model takes into account both the local vibrations on the metal sites (Piepho–Krausz–Schatz model) and the multicenter (molecular) vibrations changing the intermetallic distances (as suggested by Piepho). In the framework of the semiclassical adiabatic approach the potential surfaces are analysed and different kinds of localised and delocalised states are found. On the basis of the calculated degrees of the localisation the conventional Robin and Day classification of mixed-valence compounds is reconsidered in view of the generalised…

ChemInform Abstract: Cobalt Clusters with Cubane-Type Topologies Based on Trivacant Polyoxometalate Ligands.

Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV–vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)]4– (1) consists of a trilacunary [B-α-PW9O34]9– unit which accommodates a cubane-like {CoII4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2]9– (2), [Co7(OH)6(H2O)4(PW9O34)2]n9n– (3), and [Co7(OH)6(H2O)6(P2W15O56)2]15– (4), dicubane-like {CoII6CoIIIO8} cores are encapsulated between two heptadentate [B-α-PW9O34]9– (in…

Hybrid molecular materials formed by alternating layers of bimetallic oxalate complexes and tetrathiafulvalene molecules: Synthesis, structure, and magnetic properties of TTF4(Mn(H2O)2)[Cr(ox)3]2)·14 H2O

Spin-Polarized Hopping Transport in Magnetically Tunable Rare-Earth Quinolines

Dr. A. Bedoya-Pinto, Prof. F. Casanova, Prof. L. E. Hueso CIC nanoGUNE Consolider olosa T Hiribidea 76 , 20018 Donostia–San Sebastian , Spain E-mail: a.bedoya@nanogune.eu; l.hueso@nanogune.eu Dr. H. Prima-Garcia, Prof. E. Coronado Instituto de Ciencia Molecular (ICMoL) Universidad de Valencia C/Catedratico Jose Beltran 2 , E-46980 Valencia , Spain Prof. F. Casanova, Prof. L. E. Hueso IKERBASQUE, Basque Foundation for Science E-48011 Bilbao , Spain

Peptides as Versatile Platforms for Quantum Computing

The pursuit of novel functional building blocks for the emerging field of quantum computing is one of the most appealing topics in the context of quantum technologies. Herein we showcase the urgency of introducing peptides as versatile platforms for quantum computing. In particular, we focus on lanthanide-binding tags, originally developed for the study of protein structure. We use pulsed electronic paramagnetic resonance to demonstrate quantum coherent oscillations in both neodymium and gadolinium peptidic qubits. Calculations based on density functional theory followed by a ligand field analysis indicate the possibility of influencing the nature of the spin qubit states by means of contro…

Magnetic exchange interaction in a pair of orbitally degenerate ions: Magnetic anisotropy of [Ti2Cl9]−3

The theory of the kinetic exchange in a pair of orbitally degenerate ions developed by the authors [J. Phys. Chem. A 102, 200 (1998)] is applied to the case of face-shared bioctahedral dimer (overall D3h-symmetry). The effective kinetic exchange Hamiltonian is found for a 2T2–2T2 system taking into account all relevant transfer pathways and charge-transfer crystal field states. The influence of different transfer integrals involved in the kinetic exchange on the energy pattern and magnetic properties of the system is examined. The role of other related interactions (trigonal crystal field, spin–orbit coupling) is also discussed in detail. Using the pseudoangular momentum representation and …

New conducting radical salts based upon Keggin-type polyoxometalates and perylene

Three new radical salts, Per6[PMo12O40]·CH2Cl2 (1), Per6[PMo12O40]·CH3CN (2), and Per9(NBu4)4[SiW12O40]2 (3) (Per = perylene), have been synthesised and their electrical and magnetic properties characterised. These three salts are diamagnetic and they behave as semiconductors with room temperature conductivities of 69, 3.6 and 0.85 S cm−1. While salt 2 presents hole-type conduction and 3 exhibits electron-dominated electrical transport properties, salt 1 shows at 150 K an abrupt change in the thermal dependence of the electrical conductivity and the Seebeck coefficient suggesting a phase transition.

Liquid phase exfoliation of carbonate-intercalated layered double hydroxides.

Direct exfoliation of a carbonate layered double hydroxide (LDH) has been achieved by using a novel horn-probe sonic tip, avoiding the development of time-consuming anion-exchange reactions. The most suitable solvents were chosen based on the Hildebrand solubility parameters and the thickness of the exfoliated nanosheets confirmed unambiguously the successful delamination.

Magnetic molecular nanostructures: Design of magnetic molecular materials as monolayers, multilayers and thin films

In this paper we summarize the importance and versatility of the molecular approach in the design and development of novel magnetic molecular materials. These materials processing, in order to obtain controlled molecular structures at the nanoscale, will also be remarked.

Solid-State Electrochemical Method for Determining Core and Shell Size in Pd@PdO Nanoparticles

Electrochemical characterization of palladium nanoparticles surrounded by a palladium oxide shell (Pd@PdO) is described from a combination of voltammetry plus electrochemical quartz crystal microbalance experiments at nanoparticle deposits on graphite electrodes in contact with aqueous H2SO4 and NaOH solutions. A method for determining the metal core size and oxide shell thickness of the Pd@PdO nanoparticles, based on a combination of conventional voltammetry of nanoparticles in DMSO solution and voltammetry of nanoparticle deposits in contact with 0.10 M aqueous NaOH solution, is described.

Dynamic magnetic MOFs.

In this review we combine the use of coordination chemistry with the concepts of molecular magnetism to design magnetic Metal–Organic Frameworks (MOFs) in which the crystalline network undergoes a dynamic change upon application of an external stimulus. The various approaches so far developed to prepare these kinds of chemically or physically responsive MOFs with tunable magnetic properties are presented.

Deep-Red-Emitting Electrochemical Cells Based on Heteroleptic Bis-chelated Ruthenium(II) Complexes

Two ruthenium(II)-based complexes were prepared that show intense deep-red light emission at room temperature. Solid-state electroluminescent devices were prepared using one of the ruthenium complexes as the only active component. These devices emit deep-red light at low voltages and exhibit extraordinary stabilities, demonstrating their potential for low-cost deep-red light sources.

Nanomagnets: Quantum Rescaling, Domain Metastability, and Hybrid Domain‐Walls in 2D CrI 3 Magnets (Adv. Mater. 5/2021)

Tuning the magnetic properties in the layered molecular based magnets A[FeIIRuxIIIM1−xIII(ox)3] (MIII=Cr or Fe; ox=oxalate; A=organic or organometallic cation)

Abstract The magnetic properties of the family of layered molecular magnets A[FeIIMIII(ox)3] (MIII=Cr, Fe, Ru; ox=oxalate; A+=[NBu4]+, [ CoCp 2 ∗ ] + ) are reported. In particular, a detailed magnetic study of the solid solutions FeII(RuIIICrIII) and FeII(RuIIIFeIII) has been undertaken. We show that in these magnets both, transition temperatures and coercive fields, can be easily tuned by changing the chemical composition of the material, i.e. the ratio RuIII/MIII (MIII=Cr, Fe) within the magnetic layers and the type of cation A+ inserted in between the layers. Coercive fields as high as 2.2 T have been reached in this way.

Rational Design of Single-Ion Magnets and Spin Qubits Based on Mononuclear Lanthanoid Complexes

Here we develop a general approach to calculating the energy spectrum and the wave functions of the low-lying magnetic levels of a lanthanoid ion submitted to the crystal field created by the surrounding ligands. This model allows us to propose general criteria for the rational design of new mononuclear lanthanoid complexes behaving as single-molecule magnets (SMMs) or acting as robust spin qubits. Three typical environments exhibited by these metal complexes are considered, namely, (a) square antiprism, (b) triangular dodecahedron, and (c) trigonal prism. The developed model is used to explain the properties of some representative examples showing these geometries. Key questions in this ar…

Structural and magnetic characterization of Pd nanoparticles encapsulated in apoferritin

Pd nanoparticles exhibiting permanent magnetism at room temperature have been prepared within the apoferritin cavity. Pd nanoparticles in air and under an inert atmosphere were synthesized to study the influence of the aerobic and anaerobic conditions in the final magnetic properties. The surface of nanoparticles as well as the type of crystalline phase could determine the magnetic properties. X-ray powder diffraction, including Debye-function analysis, transmission electronic microscopy, and magnetization measurements have been used for characterizing the nanoparticles.

A “Cation-less” Oxalate-Based Ferromagnet Formed by Neutral Bimetallic Layers:  {[Co(H2O)2]3[Cr(ox)3]2(18-crown-6)2}∞ (ox = Oxalate Dianion; 18-crown-6 = C12H24O6)

Neutral layers of the bimetallic oxalate complex {[Co(H2O)2]3[Cr(ox)3]2}∞ are formed in the presence of a crown ether and stabilized by hydrogen bonding. The resulting soluble ferromagnet orders at Tc = 7.4 K.

Scanning tunneling measurements of layers of superconducting 2H-TaSe2: Evidence for a zero-bias anomaly in single layers

This work was supported by the EU (ERC Advanced Grant SPINMOL and COST MP-1201), the Spanish MINECO (Consolider-Ingenio in Molecular Nanoscience, CSD2007-00010 and projects FIS2011-23488, MAT2011-25046, MAT2011-22785 and ACI-2009-0905, co-financed by FEDER), by the Comunidad de Madrid (program Nanobiomagnet) and the Generalitat Valenciana (Programs Prometeo and ISIC-NANO)

WS2/MoS2 Heterostructures via Thermal Treatment of MoS2 Layers Electrostatically Functionalized with W3S4 Molecular Clusters

The preparation of 2D stacked layers that combine flakes of different nature, gives rise to countless number of heterostructures where new band alignments, defined at the interfaces, control the electronic properties of the system. Among the large family of 2D/2D heterostructures, the one formed by the combination of the most common semiconducting transition metal dichalcogenides WS2/MoS2, has awaken great interest due to its photovoltaic and photoelectrochemical properties. Solution as well as dry physical methods have been developed to optimize the synthesis of these heterostructures. Here a suspension of negatively charged MoS2 flakes is mixed with a methanolic solution of a cationic W3S…

Bimetallic MnIII–FeII hybrid complexes formed by a functionalized MnIII Anderson polyoxometalate coordinated to FeII: observation of a field-induced slow relaxation of magnetization in the MnIII centres and a photoinduced spin-crossover in the FeII centres

The synthesis and crystal structure of an Anderson POM functionalized with two 2,6-di(pyrazol-1-yl)-pyridine (1-bpp) ligands are reported (compound 1). High-frequency electron paramagnetic resonance (HF-EPR) and magnetic measurements show that it presents a significant negative axial zero-field splitting and field-induced slow relaxation of magnetization due to the presence of isolated MnIII anisotropic magnetic ions. Complexation of 1 with FeII gives rise to a 2D cationic network formed by Anderson POMs coordinated to two FeII ions through the two tridentate 1-bpp ligands and to other two FeII ions through two oxo ligands in compound 2, and to an anionic polymeric network formed by Anderso…

Molecular conductors based on the mixed-valence polyoxometalates [SMo12O40]n- (n = 3 and 4) and the organic donors bis(ethylenedithio)tetrathiafulvalene and bis(ethylenedithio)tetraselenafulvalene.

The synthesis, crystal structure, and physical characterization of two new radical salts formed by the organic donors bis(ethylenedithio)tetrathiafulvalene (ET) and bis(ethylenediseleno)tetrathiafulvalene (BETS) and the Keggin polyoxometalate (POM) [SMo(12)O(40)](n-) are reported. The salts isolated are ET(8)[SMo(12)O(40)] x 10 H(2)O (1) (crystal data: (1) monoclinic, space group I2/m with a = 13.9300(10) A, b = 43.467(3) A, c = 13.9929(13) A, beta = 107.979(6) degrees, V = 8058.9(11) A(3), Z = 2) and BETS(8)[SMo(12)O(40)] x 10 H(2)O (2) (crystal data: monoclinic, space group I2/m with a = 14.0878(2) A, b = 44.1010(6) A, c = 14.0930(2) A, beta = 106.739(3) degrees, V = 8384.8 A(3), Z = 2). …

Hybrid Materials Based on Magnetic Layered Double Hydroxides: A Molecular Perspective

Design of functional hybrids lies at the very core of synthetic chemistry as it has enabled the development of an unlimited number of solids displaying unprecedented or even improved properties built upon the association at the molecular level of quite disparate components by chemical design. Multifunctional hybrids are a particularly appealing case among hybrid organic/inorganic materials. Here, chemical knowledge is used to deploy molecular components bearing different functionalities within a single solid so that these properties can coexist or event interact leading to unprecedented phenomena. From a molecular perspective, this can be done either by controlled assembly of organic/inorga…

Stoichiometric Control of the Magnetic Properties in Copper( II ) Cyano‐Bridged Bimetallic Complexes

Control of the Cu2+ ion coordination environment affords a 1D, magnetically diluted compound, [Cu(cis-chxn)2]3[Fe(CN)6]2·7H2O (1) and the 2D ferromagnetic material [Cu(cis-chxn)]3[Fe(CN)6]2·6H2O (2) with a critical temperature, Tc, of 3.5 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Insights into the formation of metal carbon nanocomposites for energy storage using hybrid NiFe layered double hydroxides as precursors

[EN] NiFe-carbon magnetic nanocomposites prepared using hybrid sebacate intercalated layered double hydroxides (LDHs) as precursors are shown to be of interest as supercapacitors. Here, the low-temperature formation mechanism of these materials has been deciphered by means of a combined study using complementaryin situ(temperature-dependent) techniques. Specifically, studies involving X-ray powder diffraction, thermogravimetry coupled to mass spectrometry (TG-MS), statistical Raman spectroscopy (SRS), aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) have been carried out. The experimental results confirm the early formation o…

Improved stability of solid state light emitting electrochemical cells consisting of ruthenium and iridium complexes

ABSTRACTTwo charged organometallic complexes containing bulky hydrophobic ligands based on ruthenium (II) and iridium (III) were synthesized and their performance in solid state light emitting electrochemical cells is described. The complexes were chosen as due to their large ligands a diminished susceptibility towards the formation of destructive complexes during device operation is expected. The LEC device performances reveal the longest living devices reported so far under dc bias. Quantum chemical calculations confirm that the major effect of the bulky diphenylphenanthroline ligands is of steric origin and not related with changes in the molecular electronic structure of the complexes.

Spin Switching in Molecular Quantum Cellular Automata Based on Mixed-Valence Tetrameric Units

In this article we focus on the study of spin effects in a single square-planar mixed-valence cell comprising two electrons and in coupled molecular cells for quantum cellular automata. Using the vibronic model we demonstrate that the polarizabilities of the cell are different in spin-singlet and spin-triplet states of the electronic pair. Based on this inference the concept of spin switching in molecular quantum cellular automata is proposed, and the conditions under which this effect is feasible are derived. In order to reveal these conditions we have performed a series of quantum-mechanical calculations of the vibronic energy levels of the isolated cell and of the cell subjected to the e…

Exploiting Clock Transitions for the chemical design of resilient molecular spin qubits

Molecular spin qubits are chemical nanoobjects with promising applications that are so far hampered by the rapid loss of quantum information, a process known as decoherence. A strategy to improve this situation involves employing so-called Clock Transitions (CTs), which arise at anticrossings between spin energy levels. At CTs, the spin states are protected from magnetic noise and present an enhanced quantum coherence. Unfortunately, these optimal points are intrinsically hard to control since their transition energy cannot be tuned by an external magnetic field; moreover, their resilience towards geometric distortions has not yet been analyzed. Here we employ a python-based computational t…

High-Nuclearity Magnetic Clusters: Generalized Spin Hamiltonian and Its Use for the Calculation of the Energy Levels, Bulk Magnetic Properties, and Inelastic Neutron Scattering Spectra

A general solution of the exchange problem in the high-nuclearity spin clusters (HNSC) containing arbitrary number of exchange-coupled centers and topology is developed. All constituent magnetic centers are supposed to possess well-isolated orbitally non-degenerate ground states so that the isotropic Heisenberg-Dirac-Van Vleck (HDVV) term is the leading part of the exchange spin Hamiltonian. Along with the HDVV term, we consider higher-order isotropic exchange terms (biquadratic exchange), as well as the anisotropic terms (anisotropic and antisymmetric exchange interactions and local single-ion anisotropies). All these terms are expressed as irreducible tensor operators (ITO). This allows u…

Cover Picture: Insertion of a Single-Molecule Magnet inside a Ferromagnetic Lattice Based on a 3D Bimetallic Oxalate Network: Towards Molecular Analogues of Permanent Magnets (Chem. Eur. J. 6/2014)

Coherent Spin Dependent Landau-Zener Tunneling in Mixed Valence Dimers

In this contribution we introduce the concept of single molecule ferroelectric based on the vibronic pseudo Jahn-Teller model of mixed valence dimeric clusters belonging to the Robin and Day class II compounds. We elucidate the main factors controlling the nonadiabatic Landau-Zener tunneling between the low lying vibronic levels induced by a pulse of the electric field. The transition probabilities are shown to be dependent on the both time of the pulse and the total spin of the cluster. A possibility to control the spin-dependent Landau-Zener tunneling by applying a static magnetic field is discussed.

Modelling the properties of magnetic clusters with complex structures: how symmetry can help us

The purpose of this article is to answer the question of how symmetry helps us to investigate and understand the properties of nanoscopic magnetic clusters with complex structures. The systems of choice will be the three types of polyoxometalates (POMs): (1) POMs containing localised spins; (2) reduced mixed-valence (MV) POMs; (3) partially delocalised POMs in which localised and delocalised subunits coexist and interact. The theoretical tools based on various kinds of symmetry are the following: (1) irreducible tensor operator (ITO) approach based on the so-called 'spin-symmetry' and MAGPACK program; (2) group-theoretical assignment of the exchange multiplets based on spin- and point symme…

Modelling electric field control of the spin state in the mixed-valence polyoxometalate [GeV14O40]8−

International audience; : The two-electron reduced mixed-valence polyoxometalate [GeV14O40](8-) presents an unusual paramagnetic behaviour as a consequence of the partial trapping of these electrons. The effect of applying an electric field is that of inducing antiferromagnetic coupling between the two delocalized electronic spins.

Transient attosecond soft-X-ray spectroscopy in layered semi-metals (Conference Presentation)

X-ray absorption fine-structure (XAFS) spectroscopy is a well-established technique capable of extracting information about a material’s electronic and lattice structure with atomic resolution. While the near-edge region (XANES) of a XAFS spectrum provides information about the electronic configuration, structural information is extracted from the extended XAFS (EXAFS) spectrum, consisting of several hundreds of eV above the absorption edge. With the advent of high harmonic sources, reaching photon energies in soft x-ray (SXR) region, it now becomes possible to connect the spectroscopic capabilities of XAFS to the unprecedented attosecond temporal resolution of a high harmonic source allowi…

Charge Mobility and Dynamics in Spin-Crossover Nanoparticles Studied by Time-Resolved Microwave Conductivity

We use the electrode-less time-resolved microwave conductivity (TRMC) technique to characterize spin-crossover (SCO) nanoparticles. We show that TRMC is a simple and accurate mean for simultaneously as-sessing the magnetic state of SCO compounds and charge transport information on the nanometre length scale. In the low-spin state from liquid nitrogen temperature up to 360 K the TRMC measurements present two well-defined regimes in the mobility and in the half-life times, possessing similar transition tempera-tures TR near 225 K. Below TR, an activation-less regime associated with short lifetimes of the charge carri-ers points at the presence of shallow-trap states. Above TR, these states ar…

A Novel Chainlike Heteropolyanion Formed by Keggin Units: Synthesis and Structure of(ET)8n[PMnW11O39]n· 2nH2O

Design of Molecular Spintronics Devices Containing Molybdenum Oxide as Hole Injection Layer

Ferromagnetism in [Mn(Cp*) 2 ] + ‐Derived Complexes: the “Miraculous” Stacking in [Mn(Cp*) 2 ][Ni(dmit) 2 ]

The synthesis and characterisation (X-ray structure and magnetism) of metal complexes (Ni, Au) with the [Mn(Cp*)2]+ cation and the dmit2− and dmid2− ligands are reported. [Mn(Cp*)2][Ni(dmit)2] (1) and [Mn(Cp*)2][Au(dmit)2] (2) exhibit the same structural arrangement, built on stacks of [Ni(dmit)2]− pairs separated by two [Mn(Cp*)2]+ cations, showing a ···D+D+A−A−D+D+A−A−··· motif. On the contrary, the dmid2− derivative [Mn(Cp*)2][Ni(dmid)2]·CH3CN (3) exhibits a totally different structure, built on mixed layers composed of one [Ni(dmid)2]− unit separated by two [Mn(Cp*)2]+ cations, showing a ···D+D+A−D+D+A−···motif. The layers are separated from each other by perpendicular [Ni(dmid)2]− unit…

Spin-crossover compounds based on iron(II) complexes of 2,6-bis(pyrazol-1-yl)pyridine (bpp) functionalized with carboxylic acid and ethyl carboxylic acid

International audience; Four new salts of the iron(II) complex of the 2,6-bis(pyrazol-1-yl)pyridine ligand functionalized with a carboxylic acid group (bppCOOH) of formulas [Fe(bppCOOH)2](BF4)2 (1(BF4)2), [Fe(bppCOOH)2](CF3SO3)2·yMe2CO (1(CF3SO3)2·yMe2CO), [Fe(bppCOOH)2](AsF6)2·yMe2CO (1(AsF6)2·yMe2CO) and [Fe(bppCOOH)2](SbF6)2·yMe2CO (1(SbF6)2·yMe2CO) have been prepared and characterized together with a more complete structural and photomagnetic characterization of the previously reported [Fe(bppCOOH)2](ClO4)2 (1(ClO4)2). Furthermore, the iron(II) complex of the ethyl ester derivative of bppCOOH (bppCOOEt) has been prepared and characterized (compound [Fe(bppCOOEt)2](ClO4)2·yMe2CO, 2(ClO4)…

Spin-crossover complex encapsulation within a magnetic metal-organic framework.

The solid-state incorporation of a mononuclear iron(III) complex within the pores of a magnetic 3D metal–organic framework (MOF) in a single crystal to single crystal process leads to the formation of a new hybrid material showing both a guest-dependent long-range magnetic ordering and a spin-crossover (SCO) behaviour.

Magnetic properties of Co–Al, Ni–Al, and Mg–Al hydrotalcites and the oxides formed upon their thermal decomposition

The magnetic behaviour of Co–Al, Ni–Al, and Mg–Al hydrotalcites (HTlc) with a M2+/Al3+ molar ratio of 3 and carbonates in the interlayer, as well as the mixed oxides obtained after calcination at 823 K for 5 h, has been investigated by DC and AC magnetic susceptibility measurements and isothermal magnetisation. The samples were also characterised by ICP-OES and XRD. The magnetic measurements show that Co–Al and Ni–Al HTlcs behave as ferromagnets, with ordering temperatures of approximately 6–7 K in both cases, and displaying hysteresis loops at 2 K with coercive fields of 4.2 and 5.5 mT, respectively, whereas the Mg–Al-HTlc shows the expected diamagnetic behaviour. A solid solution of cobal…

Modeling the magnetic properties and Mössbauer spectra of multifunctional magnetic materials obtained by insertion of a spin-crossover Fe(III) complex into bimetallic oxalate-based ferromagnets.

In this article, we present a theoretical microscopic approach to describe the magnetic and spectroscopic behavior of multifunctional hybrid materials which demonstrate spin crossover and ferromagnetic ordering. The low-spin to high-spin transition is considered as a cooperative phenomenon that is driven by the interaction of the electronic shells of the Fe ions with the full symmetric deformation of the local surrounding that is extended over the crystal lattice via the acoustic phonon field. The proposed model is applied to the analysis of the series [Fe(III)(sal2-trien)] [Mn(II)Cr(III)(ox)3]·solv, in short 1·solv, where solv = CH2Cl2, CH2Br2, and CHBr3.

Metal-functionalized covalent organic frameworks as precursors of supercapacitive porous N-doped graphene

Covalent Organic Frameworks (COFs) based on polyimine with several metal ions (FeIII, CoII and NiII) adsorbed into their cavities have shown the ability to generate N-doped porous graphene from their pyrolysis under controlled conditions. These highly corrugated and porous graphene sheets exhibit high values of specific capacitance, which make them useful as electrode materials for supercapacitors.

Field dependence of the vortex core size probed by scanning tunneling microscopy

We study the spatial distribution of the density of states (DOS) at zero bias N(r) in the mixed state of single and multigap superconductors. We provide an analytic expression for N(r) based on deGennes' relationship between DOS and the order parameter that reproduces well scanning tunneling microscopy (STM) data in several superconducting materials. In the single gap superconductor β-Bi2Pd, we find that N(r) is governed by a length scale ξH=φ0/2πH, which decreases in rising fields. The vortex core size C, defined via the slope of the order parameter at the vortex center, C (dΔ/dr|r→0)-1, differs from ξH by a material dependent numerical factor. The new data on the tunneling conductance and…

Hybrid Molecular Materials Based upon Organic π-Electron Donors and Inorganic Metal Complexes. Conducting Salts of Bis(ethylenediseleno)tetrathiafulvalene (BEST) with the Octahedral Anions Hexacyanoferrate(III) and Nitroprusside

Abstract The synthesis, structure and physical characterization of three new radical salts formed by the organic donor bis(ethylenediseleno)tetrathiafulvalene (BEDS-TTF or BEST) and the paramagnetic hexacyanoferrate(III) anion [Fe(CN)6]3− or the photochromic nitroprusside anion [Fe(CN)5NO]2− are reported: (BEST)4[Fe(CN)6] (1), (BEST)3[Fe(CN)6]2·H2O (2) and (BEST)2[Fe(CN)5NO] (3). Salts 1 and 3 show a layered structure with alternating organic (β–type packing) and inorganic slabs. Salt 2 shows an original interpenetrated structure probably due to the unprecedented presence of (BEST)2+ dications. The three salts are semiconductors although salt 1 exhibits a high room temperature conductivity …

The first radical salt of the polyoxometalate cluster [P2W18O62]6⊖with bis(ethylenedithio)tetrathiafulvalene (ET): ET11[P2W18O62] · 3H2O

Magnetic Exchange between Orbitally Degenerate Ions:  A New Development for the Effective Hamiltonian

A new approach to the problem of the kinetic exchange for orbitally degenerate ions is developed. The constituent multielectron metal ions are assumed to be octahedrally coordinated, and strong crystal field scheme is employed, making it possible to take full advantage from the symmetry properties of the fermionic operators and collective electronic states. In the framework of the microscopic approach, the highly anisotropic effective Hamiltonian of the kinetic exchange is constructed in terms of spin operators and standard orbital operators (matrices of the unit cubic irreducible tensors). As distinguished from previous considerations, the effective Hamiltonian is derived for a most genera…

High nuclearity mixed-valence magnetic clusters: theoretical study of the spin coupling in the C602− fulleride ion

Abstract The problem of delocalization of a pair of electrons over the fullerene C 60 is considered, with the aim of elucidating the nature of the ground spin state, as well as the structure of the low-lying energy levels in this mixed-valence molecule C 60 2− . A model that considers the Coulomb interactions between the two extra electrons, as well as the two single-electron transfer processes involved in the electron delocalization, is developed. The influence of these electronic parameters on the spectrum of the low-lying energy levels is discussed. We find that the ground state is always a spin singlet, whatever the relative values of these parameters are.

Stimuli-responsive hybrid materials: breathing in magnetic layered double hydroxides induced by a thermoresponsive molecule

[EN] A hybrid magnetic multilayer material of micrometric size, with highly crystalline hexagonal crystals consisting of CoAl-LDH ferromagnetic layers intercalated with thermoresponsive 4-(4-anilinophenylazo)benzenesulfonate (AO5) molecules diluted (ratio 9 : 1) with a flexible sodium dodecylsulphate (SDS) surfactant has been obtained. The resulting material exhibits thermochromism attributable to the isomerization between the azo (prevalent at room temperature) and the hydrazone (favoured at higher temperatures) tautomers, leading to a thermomechanical response. In fact, these crystals exhibited thermally induced motion triggering remarkable changes in the crystal morphology and volume. In…

Multi-frequency EPR studies of a mononuclear holmium single-molecule magnet based on the polyoxometalate [Ho(III)(W5O18)2]9-.

Continuous-wave, multi-frequency electron paramagnetic resonance (EPR) studies are reported for a series of single-crystal and powder samples containing different dilutions of a recently discovered mononuclear Ho(III) (4f(10)) single-molecule magnet (SMM) encapsulated in a highly symmetric polyoxometalate (POM) cage. The encapsulation offers the potential for applications in molecular spintronics devices, as it preserves the intrinsic properties of the nanomagnet outside of the crystal. A significant magnetic anisotropy arises due to a splitting of the Hund's coupled total angular momentum (J = L + S = 8) ground state in the POM ligand field. Thus, high-frequency (50.4 GHz) EPR studies reve…

Strong enhancement of superconductivity at high pressures within the charge-density-wave states of2H−TaS2and2H−TaSe2

We present measurements of the superconducting and charge density wave critical temperatures (Tc and TCDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that Tc increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases coexisting with superconductivity within our full pressure range.

Electronic, Structural and Functional Versatility in Tetrathiafulvalene-Lanthanide Metal-Organic Frameworks

&lt;div&gt;Tetrathiafulvalene-Lanthanide (TTF-Ln) Metal-Organic Frameworks (MOFs) are an interesting class of multifunctional materials in which porosity can be combined with electronic properties such as electrical conductivity, redox activity, luminescence and magnetism. Herein we report a new family of isostructural TTF-Ln MOFs, denoted as &lt;b&gt;MUV-5(Ln)&lt;/b&gt; (Ln = Gd, Tb, Dy, Ho, Er), exhibiting semiconducting properties as a consequence of the short intermolecular S···S contacts established along the chain direction between partially oxidised TTF moieties. In addition, this family shows photoluminescence properties and single-molecule magnetic behaviour, finding near-infrared …

Nanomechanical probing and strain tuning of the Curie temperature in suspended Cr2Ge2Te6-based heterostructures

AbstractTwo-dimensional magnetic materials with strong magnetostriction are attractive systems for realizing strain-tuning of the magnetization in spintronic and nanomagnetic devices. This requires an understanding of the magneto-mechanical coupling in these materials. In this work, we suspend thin Cr2Ge2Te6 layers and their heterostructures, creating ferromagnetic nanomechanical membrane resonators. We probe their mechanical and magnetic properties as a function of temperature and strain by observing magneto-elastic signatures in the temperature-dependent resonance frequency near the Curie temperature, TC. We compensate for the negative thermal expansion coefficient of Cr2Ge2Te6 by fabrica…

Building Multifunctionality in Hybrid Materials

Multifunctional magnetic materials obtained by insertion of a spin-crossover Fe(III) complex into bimetallic oxalate-based ferromagnets.

The syntheses, structures and magnetic properties of the compounds of formula [Fe(III)(sal(2)-trien)][Mn(II)Cr(III)(ox)(3)].CH(2)Cl(2) (1; H(2)sal(2)-trien=N,N'-disalicylidenetriethylenetetramine, ox=oxalate), [Fe(III)(sal(2)-trien)][Mn(II)Cr(III)(ox)(3)].CH(3)OH (2), [In(III)(sal(2)-trien)][Mn(II)Cr(III)(ox)(3)].0.25H(2)O.0.25CH(3)OH.0.25CH(3)CN (3), and [In(III)(sal(2)-trien)][Mn(II)Cr(III)(ox)(3)].CH(3)NO(2).0.5H(2)O (4) are reported. The structure of 1 presents a 2D honeycomb anionic layer formed by Mn(II) and Cr(III) ions linked through oxalate ligands and a cationic layer of [Fe(sal(2)-trien)](+) complexes intercalated between the 2D oxalate network. The structures of 2, 3, and 4 pres…

A Novel Polyoxotungstate Containing atriangulo Ni3II Cluster with Ferromagnetic Exchange Interactions and anS= 3 Ground State

Dual-emitting Langmuir-Blodgett film-based organic light-emitting diodes.

Langmuir-Blodgett (LB) films containing alternating layers of the metallosurfactants bis(4,4'-tridecyl-2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium(II)-bis(chloride) (1) and bis[2-(2,4-difluorophenyl)pyridine](4,4'-dinonadecyl-2,2'-bipyridine)iridium(III) chloride (2) have been prepared. Langmuir monolayers at the air-water interface of 1 and 2 with different anions in the subphase have been characterized by pi-A compression isotherms and Brewster angle microscopy (BAM). The transferred LB films have been characterized by IR, UV-vis and emission spectroscopy, and atomic force microscopy (AFM). Electroluminescent devices formed by LB films containing alternating layers of thes…

Molecular spin qubits based on lanthanide ions encapsulated in cubic polyoxopalladates: design criteria to enhance quantum coherence

The family of cubic polyoxopalladates encapsulating lanthanide ions [LnPd12(AsPh)8O32]5− where Ln = Tb, Dy, Ho, Er and Tm, is magnetically characterised and theoretically described by the Radial Effective Charge (REC) model and a phenomenological crystal-field approach using the full-hamiltonian, in the SIMPRE and CONDON packages respectively. The lack of anisotropy generates an extraordinarily rich energy level structure at low temperatures, which allows us to study how such a structure is affected by lifting the strict cubic symmetry and/or by applying an external magnetic field. In particular, we will explore the possibility of using these cubic Ln complexes as spin-qubits. We will focus…

Quantum rescaling, domain metastability and hybrid domain-walls in two-dimensional CrI3 magnets

Higher-order exchange interactions and quantum effects are widely known to play an important role in describing the properties of low-dimensional magnetic compounds. Here we identify the recently discovered two-dimensional (2D) van der Waals (vdW) CrI3 as a quantum non-Heisenberg material with properties far beyond an Ising magnet as initially assumed. We find that biquadratic exchange interactions are essential to quantitatively describe the magnetism of CrI3 but requiring quantum rescaling corrections to reproduce its thermal properties. The quantum nature of the heat bath represented by discrete electron-spin and phonon-spin scattering processes induced the formation of spin fluctuations…

Light-induced decarboxylation in a photo-responsive iron-containing complex based on polyoxometalate and oxalato ligands.

A new iron-oxalato polyoxometalate exhibits a remarkable photocoloration effect in the solid state based entirely on an intramolecular process.

Spin-crossover iron(ii) complex showing thermal hysteresis around room temperature with symmetry breaking and an unusually high T(LIESST) of 120 K.

We report a Fe(II) complex based on 4′,4′′ carboxylic acid disubstituted dipyrazolylpyridine that shows a spin-crossover close to room temperature associated to a crystallographic phase transition and the LIESST effect with a high T(LIESST) of 120 K.

Origin of the large spectral shift in electroluminescence in a blue light emitting cationic iridium(III) complex

A new, but archetypal compound [ Ir( ppy- F-2) (2)Me(4)phen] PF6, where ppy- F2 is 2-(2',4'- fluorophenyl) pyridine and Me(4)phen is 3,4,7,8- tetramethyl- 1,10- phenanthroline, was synthesized and used to prepare a solid-state light-emitting electrochemical cell (LEEC). This complex emits blue light with a maximum at 476 nm when photoexcited in a thin film, with a photoluminescence quantum yield of 52%. It yields an efficient single-component solid-state electroluminescence device with a current efficiency reaching 5.5 cd A(-1) and a maximum power efficiency of 5.8 Lm Watt(-1). However, the electroluminescence spectrum is shifted with respect to the photoluminescence spectrum by 80 nm resul…

Hybrid Magnetic Multilayers by Intercalation of Cu(II) Phthalocyanine in LDH Hosts

The intrinsic flexibility of layered double hydroxides (LDHs) has been here exploited to design hybrid multilayered materials by intercalation of the copper phthalocyaninetetrasulfonate (CuPcTs) complex in the interlamellar space offered by these layered hosts through a simple anion-exchange procedure. Taking advantage of their chemical versatility, two different LDHs, the diamagnetic ZnAl and the ferromagnetic NiAl, have been synthesized and characterized to explore the differences in the magnetic properties of the hybrids introduced by the intercalation of the paramagnetic complex.

Reversible Colorimetric Probes for Mercury Sensing

The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and N749 [(2,2':6',2' '-terpyridine-4,4',4' '-tricarboxylate)ruthenium(II) tris(tetrabutylammonium) tris(isothiocyanate)] are described. It was found that mercury ions coordinate reversibly to the sulfur atom of the dyes' NCS groups. This interaction induces a color change in the dyes at submicromolar concentrations of mercury. Furthermore, the color change of these dyes is selective for mercury(II) when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II). The detection limit…

Synthesis, characterization and magnetism of monodispersed water soluble palladium nanoparticles

Water soluble, monodispersed Pd nanoparticles with a narrow particle size distribution have been successfully synthesized by controlled reduction of [PdCl4]2−. The resulting aqueous colloids are stable over extended periods of time and can be prepared at high nanoparticle loading (20 g/L of Pd) with no agglomeration. The size of the nanoparticles can be reduced from the nanometer (ca. 3.5 nm) to the sub-nanometer size range (ca. 0.9 nm). Detailed magnetic characterization indicated that the larger, 3.5 nm nanoparticles show ferromagnetic properties at room temperature, while the sub-nanometric ones lose this magnetic behavior.

Imaging the Magnetic Reversal of Isolated and Organized Molecular-Based Nanoparticles using Magnetic Force Microscopy

In the race towards miniaturization in nanoelectronics, magnetic nanoparticles (MNPs) have emerged as potential candidates for their integration in ultrahigh-density recording media. Molecular-based materials open the possibility to design new tailor-made MNPs with variable composition and sizes, which benefit from the intrinsic properties of these materials. Before their implementation in real devices is reached, a precise organization on surfaces and a reliable characterization and manipulation of their individual magnetic behavior are required. In this paper, it is demonstrated how molecular-based MNPs are accurately organized on surfaces and how the magnetic properties of the individual…

Magnetic order and local field distribution in the hybrid magnets [FeCp*(2)][MnCr(ox)(3)] and [CoCp*(2)][FeFe(ox)(3)]: a muon spin relaxation study

Zero-field muon spin relaxation (μ+SR) measurements on materials from the series [ZIIICp*2][M IIMIII(ox)3] show precession signals at several frequencies, characteristic of quasistatic magnetic fields at up to three distinct muon sites.

Molecular anisotropy analysis of single-ion magnets using an effective electrostatic model.

Simple electrostatic models have been shown to successfully rationalize the magnetic properties of mononuclear single molecule magnets based on f-elements and even to predict the direction of the magnetic anisotropy axis in these nanomagnets. In this Article, we go a step forward by showing that these models, conveniently modified to account for the covalency effects, are able to predict not only the easy axis direction but also the three components of the magnetic anisotropy. Thus, by using a lone pair effective charge (LPEC) model we can fully reproduce the angular dependence of the magnetic susceptibility in single crystals of pentamethylcyclopentadienyl-Er-cyclooctatetraene single-ion m…

Single-molecule magnetic behavior in a neutral terbium(III) complex of a picolinate-based nitronyl nitroxide free radical

The terdentate anionic picolinate-based nitronyl nitroxide (picNN) free radical forms neutral and robust homoleptic complexes with rare earth-metal ions. The nonacoordinated Tb3+ complex Tb(picNN)3• 6H2O is a single-molecule magnet with an activation energy barrier Δ = 22.8 ± 0.5 K and preexponential factor τ0 = (5.5 ± 1.1) × 10-9 s. It shows magnetic hysteresis below 1 K. © 2011 American Chemical Society.

Origin of the Paramagnetic Properties of the Mixed‐Valence Polyoxometalate [GeV 14 O 40 ] 8– Reduced by Two Electrons: Wave Function Theory and Model Hamiltonian Calculations

The aim of the work is to give an explanation of the magnetic properties of a mixed-valence [GeV14O40]8– polyoxometalate reduced by two electrons, which, in contrast to what happens in other two-electron-reduced polyoxometalates, does not show any magnetic coupling between the two unpaired electrons. For this purpose, a quantitative evaluation of the microscopic electronic parameters (electron transfer, magnetic coupling, magnetic orbital energy, and Coulomb repulsion) of the mixed-valence polyoxometalate cluster is performed. The parameters are extracted from valence-spectroscopy large configuration interaction (CI) calculations on embedded fragments. Then, these parameters are used in an …

Synthesis, crystal structures and magnetic properties of mononuclear tris(croconate)ferrate(III) complexes

Abstract A straightforward synthetic method to prepare mononuclear croconato-containing iron (III) complexes, (A)3[Fe(C5O5)3] [A = tetrabutylammonium = n-Bu4N+ (1) and tetraphenylphosphonium = PPh 4 + ( 2 ) ; C 5 O 5 2 - = croconate = dianion of 4 , 5 - dihydroxycyclopent - 4 - ene - 1 , 2 , 3 - trione ] along with their crystal structures and magnetic properties, are reported. The Fe(III) atom adopts a pseudo-octahedral geometry while magnetic susceptibility measurements, in the 2–300 K temperature range, show the occurrence of a high spin state (S = 5/2) in both complexes.

ChemInform Abstract: Catenanes and Threaded Systems: From Solution to Surfaces

Functional catenanes and threaded systems able to perform controllable mechanical motions are ideally suited for the design of molecular devices displaying mechanical, electronic, information or sensing functions. These systems have been extensively studied in solution phase and numerous examples of stimuli-driven molecular shuttles have been reported. However, for fully developing their potential applications, they must be interfaced with the macroscopic world. To achieve this objective, in the last few years catenanes and rotaxanes have been organized over surfaces in the form of chemisorbed monolayers or physisorbed monolayers, multilayers and thin films. This tutorial review summarizes …

Solid-state electrochemistry of LDH-supported polyaniline hybrid inorganic–organic material

Abstract The solid-state electrochemistry of a Zn–Al layered double hydroxide-supported polyaniline material (LDH-PANI) in contact with aqueous electrolytes is described. Interconversion processes between different forms (emeraldine, protoemeraldine, leucoemeraldine, nigraniline and pernigraniline) of the LDH-supported polyaniline units are involved in redox processes. This material exhibits significant variations of impedance upon application of different conditioning potentials, acting as an electrochemical frequency filter. Using Fe (CN) 6 4 - as redox probe, LDH-PANI can be used as a chemical–electrochemical information processing system equivalent to different combinational logic circu…

Intercalation of [M(ox)3]3− (M=Cr, Rh) complexes into NiIIFeIII-LDH

Abstract Layered Double Hydroxides (LDH) containing paramagnetic NiII and FeIII ions in the hydroxide layers and chromium or rhodium oxalate complexes at the interlayer space were prepared by ion exchange from a NiFe-LDH precursor with sebacate anions between the hydroxide layers. The precursor was synthesized by coprecipitation at controlled pH in order to avoid the formation of solid phases different from LDH. Magnetic studies demonstrated that both LDHs, NiFe–Cr(ox)3 and NiFe–Rh(ox)3, exhibited a behaviour similar to the precursor. Nevertheless, the substitution of intercalated sebacate anions with oxalate complexes compresses the LDH basal spacing, increasing the intensity of dipolar in…

Magnetic LB films based upon polyoxometalate clusters and single molecule nanomagnets

Abstract By using the adsorption properties of polyoxometalates such as the ferromagnetic cluster [Co 4 (H 2 O) 2 (PW 9 O 34 ] 10− ) along a positively charged monolayer, we have prepared well organized monolayers of the magnetic polyanions. A similar procedure allowed us to obtain Langmuir-Blodgett films (LB films) based on Mn 12 clusters which show a marked hysteresis

New BEDT-TTF/[Fe(C5O5)3]3- Hybrid System:  Synthesis, Crystal Structure, and Physical Properties of a Chirality-Induced α Phase and a Novel Magnetic Molecular Metal

The paramagnetic and chiral anion [Fe(C5O5)3]3- (C5O52-=croconate) has been combined with the organic donor BEDT-TTF (=ET=bis(ethylenedithio)tetrathiafulvalene) to synthesize a novel paramagnetic semiconductor with the first chirality-induced alpha phase, alpha-(BEDT-TTF)5[Fe(C5O5)3].5H2O (1), and one of the few known paramagnetic molecular metals, beta-(BEDT-TTF)5[Fe(C5O5)3].C6H5CN (2). Both compounds present layers of BEDT-TTF molecules, with the alpha or beta packing modes, alternating with layers containing the high-spin S=5/2 Fe(III) anions and solvent molecules. In the alpha phase, the alternation of the chiral [Fe(C5O5)3]3- anions along the direction perpendicular to the BEDT-TTF cha…

Multifunctionality in hybrid molecular materials: design of ferromagnetic molecular metals and hybrid magnets

We report on the synthesis and physical properties of novel hybrid organic–inorganic molecular materials combining ferromagnetic bimetallic oxalato-based networks and functional organic molecules as the donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) or cationic nitroxide free radicals. # 2002 Elsevier Science B.V. All rights reserved.

Role of the electron transfer and magnetic exchange interactions in the magnetic properties of mixed-valence polyoxovanadate complexes.

International audience; Modeling the properties of high-nuclearity, high-electron-population, mixed-valence (MV) magnetic systems remains one of the open challenges in molecular magnetism. In this work, we analyze the magnetic properties of a series of polyoxovananadate clusters of formula [V 18O 42] (12-) and [V 18O 42] (4-). The first compound is a fully localized spin cluster that contains 18 unpaired electrons located at the metal sites, while the second one is a MV cluster with 10 unpaired electrons largely delocalized over the 18 metal sites. A theoretical model that takes into account the interplay between electron transfer and magnetic exchange interactions is developed to explain t…

Spin qubits with electrically gated polyoxometalate molecules

Spin qubits offer one of the most promising routes to the implementation of quantum computers. Very recent results in semiconductor quantum dots show that electrically-controlled gating schemes are particularly well-suited for the realization of a universal set of quantum logical gates. Scalability to a larger number of qubits, however, remains an issue for such semiconductor quantum dots. In contrast, a chemical bottom-up approach allows one to produce identical units in which localized spins represent the qubits. Molecular magnetism has produced a wide range of systems with tailored properties, but molecules permitting electrical gating have been lacking. Here we propose to use the polyox…

Sensing of the Molecular Spin in Spin-Crossover Nanoparticles with Micromechanical Resonators

In the past years, the use of highly sensitive silicon microelectromechanical cantilevers has been proposed as a tool to characterize the spin-crossover phenomenon by employing fast optical readout of the motion. In this work, Fe II -based spin-crossover nanoparticles of the well-known [Fe(Htrz) 2 (trz)](BF 4 ) complex wrapped with thin silica shells of different sizes will be studied by means of silicon microresonators. The silica shell will enhance its chemical stability, whereas the low thickness will allow a proper mechanical coupling between the cantilever and the spin-crossover core. To maximize the sensing of the spin-crossover phenomena, different cantilever geometries and flexural…

Langmuir–Blodgett films based on inorganic molecular complexes with magnetic or optical properties

Langmuir and Langmuir–Blodgett (LB) films of a great variety of molecular metal complexes with interesting magnetic or optical properties have been prepared in the last few years. Some of the results obtained by our group and others are summarized in this article. (i) LB films of polyoxometalates (POM) were first prepared taking advantage of the adsorption properties of these cluster anions along a positively charged monolayer of an organic surfactant spread in water. A correct choice of the POM allowed the preparation of LB films with magnetic, electrochromic, or luminescent properties. Besides this semiamphiphilic method, two new methods to prepare LB films of POMs have been developed by …

Hybrid magnetic materials formed by ferritin intercalated into a layered double hydroxide

A hybrid magnetic material formed by ferritin intercalated into a layered double hydroxide (LDH) of Mg and Al (Mg/Al molar ratio 2) is prepared and characterized through powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, electron probe microanalysis (EPMA) and high resolution transmission electron microscopy (HRTEM). One observes an enhancement in the thermal stability of the ferritin molecules when they are inserted in the layered material. Magnetic measurements of the hybrid material exhibit the typical superparamagnetic behaviour of the ferritin molecule. On the other hand, the intercalation of ferritin into the LDH guarante…

Giant Enhancement in the Supercapacitance of NiFe–Graphene Nanocomposites Induced by a Magnetic Field

The rapid rise in energy demand in the past years has prompted a search for low-cost alternatives for energy storage, supercapacitors being one of the most important devices. It is shown that a dramatic enhancement (≈1100%, from 155 to 1850 F g-1 ) of the specific capacitance of a hybrid stimuli-responsive FeNi3 -graphene electrode material can be achieved when the charge/discharge cycling is performed in the presence of an applied magnetic field of 4000 G. This result is related to an unprecedented magnetic-field-induced metal segregation of the FeNi3 nanoparticles during the cycling, which results in the appearance of small Ni clusters (<5 nm) and, consequently, in an increase in pseudoca…

Thermal- and photo-induced spin crossover in the 1D coordination polymer [Fe(4-tBupy)3][Au(CN)2]2 (4-tBupy = 4-tert-butylpyridine)

Reaction of the unidentate pyridine ligand containing a bulky t-butyl substituent with Fe2+ and [Au(CN)2]− affords a new type of spin crossover (SCO) coordination polymer in the 1D compound [Fe(4-tBupy)3][Au(CN)2]2⋅0.5H2O (1), which is formed by chains of Fe(II) complexes linked through bridging [Au(CN)2]− with three terminal 4-tBupy and one monodentate [Au(CN)2]− ligands completing the octahedral coordination around Fe(II). Longer reaction times led to the minor products [Fe(4-tBupy)2][Au(CN)2]2 (2), which presents a 2D structure more similar to that found in the other SCO compounds based on [Au(CN)2]−, and the 1D compound [Fe(4-tBupy)2(MeOH)][Au(CN)2]2 (3), in which one of the three termi…

Spin states, vibrations and spin relaxation in molecular nanomagnets and spin qubits: a critical perspective

Spin–vibration coupling has been proven to be crucial for spin dynamics; theoretical studies are now addressing this experimental challenge.

Quantum Rescaling, Domain Metastability, and Hybrid Domain-Walls in 2D CrI3 Magnets

Higher-order exchange interactions and quantum effects are widely known to play an important role in describing the properties of low-dimensional magnetic compounds. Here, the recently discovered 2D van der Waals (vdW) CrI3 is identified as a quantum non-Heisenberg material with properties far beyond an Ising magnet as initially assumed. It is found that biquadratic exchange interactions are essential to quantitatively describe the magnetism of CrI3 but quantum rescaling corrections are required to reproduce its thermal properties. The quantum nature of the heat bath represented by discrete electron–spin and phonon–spin scattering processes induces the formation of spin fluctuations in the …

A molecular chemical approach to the magnetic multilayers

Abstract Using the bi-dimensional bimetallic networks based upon oxalate complexes, it is possible to prepare new multilayered materials by insertion of ‘electroactive’ molecules in between these layers. According to this approach a new family of compounds presenting alternating ferromagnetic—paramagnetic layers have been successfully prepared. Here we present the magnetic and specific heat characterization.

Path to Overcome Material and Fundamental Obstacles in Spin Valves Based on MoS2 and Other Transition-Metal Dichalcogenides

The recent introduction of two-dimensional materials into magnetic tunnel junctions (2D MTJs) offers very promising properties for spintronics, such as atomically defined interfaces, spin filtering, perpendicular anisotropy, and modulation of spin-orbit torque. Nevertheless, the difficulty of integrating exfoliated 2D materials into spintronic devices has limited exploration. Here the authors find a fabrication process leading to superior performance in MTJs based on transition-metal dichalcogenides, and further suggest a path to alleviate basic issues of technology and physics for 2D MTJs.

Zero-bias conductance peak in detached flakes of superconducting 2H-TaS2probed by scanning tunneling spectroscopy

We report an anomalous tunneling conductance with a zero-bias peak in flakes of superconducting 2$H$-${\mathrm{TaS}}_{2}$ detached through mechanical exfoliation. To explain the observed phenomenon, we construct a minimal model for a single unit cell layer of superconducting 2$H$-${\mathrm{TaS}}_{2}$ with a simplified two-dimensional Fermi surface and a sign-changing Cooper-pair wave function induced by Coulomb repulsion. Superconductivity is induced in the central $\ensuremath{\Gamma}$ pocket, where it becomes nodal. We show that weak scattering at the nodal Fermi surface, produced by nonperturbative coupling between tip and sample, gives Andreev states that lead to a zero-bias peak in the…

A chirality-induced alpha phase and a novel molecular magnetic metal in the BEDT-TTF/tris(croconate)ferrate(iii) hybrid molecular system

The novel paramagnetic and chiral anion [Fe(C5O5)3]32 has been combined with the organic donor BEDT-TTF (= ET = bis(ethylenedithio)tetrathiafulvalene) to yield the first chirality- induced α phase and a paramagnetic metal. Gomez Garcia, Carlos, Carlos.Gomez@uv.es ; Coronado Miralles, Eugenio, Eugenio.Coronado@uv.es ; Gimenez Saiz, Carlos, Carlos.Gimenez@uv.es

Graphene enhances the magnetoresistance of FeNi3nanoparticles in hierarchical FeNi3–graphene nanocomposites

An increase in the giant magnetoresistance of FeNi3 nanoparticles of 20 times has been observed in FeNi3–graphene nanocomposites synthesized using NiFe-layered double hydroxide hybrids as precursors. The magnetic, transport and magneto-transport properties of these nanocomposites are studied and compared with those of the pure FeNi3 nanoparticles. The hierarchical structure and hybrid composition of these magnetic nanocomposites lead to the observation of two unusual magneto-transport properties, namely (i) an enhancement in the low-field magnetoresistance effects, and (ii) a crossover from negative to positive MR upon cooling down the sample.

Ein aus Keggin-Einheiten aufgebautes, kettenartiges Heteropolyanion: Synthese und Struktur von (ET)8n[PMnW11O39]n · 2nH2O

Charge transfer interactions in self-assembled single walled carbon nanotubes/Dawson–Wells polyoxometalate hybrids

We demonstrate the success in self-assembling pyrene-modified Dawson–Wells-type polyoxometalates (POMs) with single walled carbon nanotubes (SWCNTs) by means of π–π interactions. In this context, the immobilization of POMs onto SWCNTs is corroborated by aberration-corrected high-resolution electron microscopy, thermogravimetric analysis, and Raman spectroscopy. From steady-state and time-resolved photophysical techniques we derived evidence for mutual interactions between SWCNTs and POMs in the excited states. The latter are the inception to a charge transfer from the SWCNTs to the POMs. Our results corroborate the suitability of POM–SWCNTs assemblies for photoactive molecular devices.

Heteroleptic Iron(II) Spin-Crossover Complexes Based on a 2,6-Bis(pyrazol-1-yl)pyridine-type Ligand Functionalized with a Carboxylic Acid

Two new heteroleptic complexes [Fe- (1bppCOOH)(3bpp-bph)](ClO4)2·solv (1·solv, solv = various solvents; 1bppCOOH = 2,6-bis(1H-pyrazol-1-yl)- isonicotinic acid; 3bpp-bph = 2,6-bis(5-([1,1′-biphenyl]-4- yl)-1H-pyrazol-3-yl)pyridine) and [Fe(1bppCOOH)- (1bppCOOEt)](ClO4)2 ·0.5Me2CO (2·0.5Me2CO, 1bppCOOEt = ethyl 2,6-bis(1H-pyrazol-1-yl)isonicotinate) were designed and prepared. The heteroleptic compound 1· solv was obtained by the combination of stoichiometric amounts of Fe(ClO4)2, 1bppCOOH, and 3bpp-bph, and it was designed to fine-tune the spin crossover (SCO) properties with respect to the previously reported homoleptic compound [Fe(1bppCOOH)2](ClO4)2. Indeed, the introduction of a new subs…

Hybrid Molecular Materials Based upon Magnetic Polyoxometalates and Organic π-Electron Donors:  Syntheses, Structures, and Properties of Bis(ethylenedithio)tetrathiafulvalene Radical Salts with Monosubstituted Keggin Polyoxoanions

International audience; The syntheses, crystal structures, and physical properties of the series of radical salts made with bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) and monosubstituted α-Keggin polyoxoanions of formula [XZ(H2O)M11O39]5- (XZM11 = Si(IV)Fe(III)Mo11, Si(IV)Cr(III)W11, P(V)Con(II)W11, P(V)Ni(II)W11, P(V)Cu(II)W11 P(V)Zn(II)W11, P(V)Mn(II)W11, and P(V)Mn(II)Mo11) containing a magnetic metal ion Z on a peripheral octahedral site of the Keggin union are reported. They all crystallize in two related series called α2 and α3. The general structure consists of alternating layers of the organic donor and the Keggin polyoxometalates. While the stoichiometry and α-packing a…

Incorporation of Mn12single molecule magnets into mesoporous silica

The incorporation of four Mn12 derivatives, namely [Mn12O12(O2CR)16(H2O)4] (R = CH3 (1), CH3CH2 (2), C6H5 (3), C6F5 (4)), into the hexagonal channels of the MCM-41 mesoporous silica has been studied. Only the smallest clusters 1 and 2, i.e. those with compatible size with the pores of MCM-41, could enter into the mesoporous silica. Powder X-ray diffraction analysis, HRTEM images and N2 adsorption–desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn12 clusters are inside the pores. The magnetic properties of the MCM-41/2b nanocomposite material obtained in CH2Cl2 indicate that the structure of the cluster is maintained after in…

Electronic and magnetic properties of Mn 12 molecular magnets on sulfonate and carboxylic acid prefunctionalized gold surfaces

Structural, electronic, and magnetic properties of [Mn 12O 12(bet) 16(EtOH) 4](PF 6) 14·4CH 3CN·H 2O (in short Mn 12bet, bet = betaine = +N(CH 3) 3-CH 2-COO -) single-molecule magnets (SMMs) deposited on previously functionalized gold surfaces have been investigated. Self-assembled monolayers (SAMs) either of sodium mercaptoethanesulfonate (MES) or mercaptopropionic acid (MPA) are used as functionalization to avoid the direct interaction between the Mn 12bet molecules and the Au surface with the aim of preserving the main functional properties of the molecules. Scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) analysis show deposited Mn 12bet SMMs well-isolated …

Field-induced slow relaxation of magnetization in a mononuclear Co(II) complex of 2,6-bis(pyrazol-1-yl)pyridine functionalized with a carboxylic acid

Abstract Combining Co(II) with the 2,6-bis-(pyrazol1-yl)pyridine ligand functionalized with a carboxylic acid group (bppCOOH) results in the compound [CoII(bppCOOH)2](ClO4)2·2Me2CO, which shows a field-induced slow relaxation of magnetization as a result of the magnetic anisotropy of the distorted octahedral coordination of high-spin Co(II). Co(II)/Fe(II) solid solutions of bppCOOH have been prepared to study the influence of Co(II) on the spin crossover properties of Fe(II). Magnetic characterization of [Fe0.92Co0.08(bppCOOH)2](ClO4)2 indicates that the Cobalt dopant leads to a reduction of T1/2 and a loss of cooperativity of the spin transition.

White hybrid organic-inorganic light-emitting diode using ZnO as the air-stable cathode

An efficient white light emitting hybrid organic−inorganic device utilizing air-stable metal oxides as anode and cathode and a polyfluorene mixed with a phosphorescent iridium complex as the emitting material is presented.

Photo-switching in a hybrid material made of magnetic layered double hydroxides intercalated with azobenzene molecules.

Financial support from the EU (Projects HINTS FP7-263104-2 and SpinMol Advanced Grant ERC-2009-AdG-20090325), the Spanish Ministerio de Economia y Competitividad (Projects with FEDER cofinancing MAT 2009-14528-C02-01, MAT2011-22785, MAT2012-38567-C02-01, CTQ-2011-26507, Consolider-Ingenio in Molecular Nanoscience CSD2007-00010, Consolider-Ingenio 2010-Multicat CSD2009-00050, and Severo Ochoa Program SEV-2012-0267), Generalitat Valenciana (PROMETEO and ISIC-Nano programs), and VLC/Campus Microcluster "Functional Nanomaterials and Nanodevices" is gratefully acknowledged. C. M. G. thanks the Spanish MINECO for a Ramon y Cajal Fellowship (RYC-2012-10894). We also acknowledge P. Atienzar and J. …

Magnetic properties of MoS 2 nanotubes doped with lithium

DC magnetization measurements of lithium-doped molybdenum sulfide nanotubes (LixMoS2, 2.2 10 kOe, the nonlinear part in H<5 kOe with saturation at approximately 10 kOe can be observed. This suggests a formation of ferromagnetic clusters even at room temperature. No magnetic phase transition between 2 and 300 K has been detected.

Magnetic Excitations in Polyoxometalate Clusters Observed by Inelastic Neutron Scattering:  Evidence for Ferromagnetic Exchange Interactions and Spin Anisotropy in the Tetrameric Nickel(II) Cluster [Ni4(H2O)2(PW9O34)2]10- and Comparison with the Magnetic Properties

The ground-state properties of the tetranuclear Ni2+ cluster [Ni4(H2O)2(PW9O34)2]10- were investigated by combining magnetic susceptibility and magnetization measurements with a detailed inelastic neutron scattering (INS) study on a fully deuterated sample of K6Na4[Ni4(H2O)2(PW9O34)2]·24H2O. The temperature dependence of the magnetic susceptibility indicates a ferromagnetic coupling of the four constituent Ni2+ ions (s = 1), and a low-temperature magnetization study provides the magnitude of the S = 4 ground-multiplet splitting due to the single-ion anisotropy of the Ni2+ ions. Besides a more direct and precise determination of the anisotropic S = 4 ground-multiplet splitting, INS enabled t…

Metallic Charge‐Transfer Salts of Bis(ethylenedithio)tetrathiafulvalene with Paramagnetic Tetrachloro(oxalato)rhenate(IV) and Tris(chloranilato)ferrate(III) Anions

The synthesis, crystal structure and physical characterization of three radical salts of the donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) and tetrachloro(oxalato)rhenate(IV) {[ReCl4(C2O4)]2–} or tris(chloranilato)ferrate(III) {[Fe(C6O4Cl2)3]3–} anions are reported. The isolated salts with ReIV are (ET)[ReCl4(C2O4)] [1, monoclinic, space group C2/c with a = 18.3409(3) A, b = 10.8414(2) A, c = 11.1285(3) A, β = 99.9714(7)°, V = 2179.38(8) A3, Z = 4] and (ET)4[ReCl4(C2O4)]·C6H5CN [2, monoclinic, space group P21/c with a = 11.8549(2) A, b = 32.9079(5) A, c = 36.4154(5) A, β = 96.742(2)°, V = 14108.1(4) A3, Z = 8]. The salt with FeIII is (ET)6[Fe(C6O4Cl2)3]·(H2O)1.5·(CH2Cl2)0.5 […

Molecular Materials from Polyoxometalates

The present article highlights recent results and provide a perspective of the interest of polyoxometalates as inorganic component of molecular materials with active physical properties. Three different aspects will be presented: i) The interest of the magnetic and mixed valence clusters provided by polyoxometalate chemistry in molecular magnetism; ii) The use of these inorganic anions as magnetic component of crystalline conducting materials based on organic donor molecules; iii) The construction of well-organized films of polyoxometalate monolayers by using the Langmuir-Blodgett technique.

Unusual Magnetic State in Lithium-DopedMoS2Nanotubes

We report on the very peculiar magnetic properties of an ensemble of very weakly coupled lithium-doped MoS2 nanotubes. The magnetic susceptibility chi of the system is nearly 3 orders of magnitude greater than in typical Pauli metals, yet there is no evidence for any instability which would alleviate this highly frustrated state. Instead, the material exhibits peculiar paramagnetic stability down to very low temperatures, with no evidence of a quantum critical point as T-->0 in spite of clear evidence for strongly correlated electron behavior. The exceptionally weak intertube interactions appear to lead to a realization of a near-ideal one-dimensional state in which fluctuations prevent the…

Proximity Effects on the Charge Density Wave Order and Superconductivity in Single-Layer NbSe2

Collective electronic states such as the charge density wave (CDW) order and superconductivity (SC) respond sensitively to external perturbations. Such sensitivity is dramatically enhanced in two dimensions (2D), where 2D materials hosting such electronic states are largely exposed to the environment. In this regard, the ineludible presence of supporting substrates triggers various proximity effects on 2D materials that may ultimately compromise the stability and properties of the electronic ground state. In this work, we investigate the impact of proximity effects on the CDW and superconducting states in single-layer (SL) NbSe2 on four substrates of diverse nature, namely, bilayer graphene…

A thermally/chemically robust and easily regenerable anilato-based ultramicroporous 3D MOF for CO 2 uptake and separation

The combination of the properly designed novel organic linker, 3,6-N-ditriazoyil-2,5-dihydroxy-1,4-benzoquinone (trz2An), with CoII ions results in a 3D ultramicroporous MOF with high CO2 uptake capacity and separation efficiency, with particular attention to CO2/N2 and CO2/CH4 gas mixtures. This material consists of 1D chains of octahedrally coordinated CoII ions linked through the anilato ligands in the equatorial positions and to the triazole substituents from two neighbouring chains in the two axial positions. This leads to a 3D microporous structure with voids with an affinity for CO2 molecules and channels that enable the selective entrance of CO2 but not of molecules with larger kine…

Influence of Peripheral Substitution on the Magnetic Behavior of Single-Ion Magnets Based on Homo- and Heteroleptic TbIIIBis(phthalocyaninate)

A series of homoleptic ([Tb(III)(Pc)(2) ]) and heteroleptic ([Tb(III)(Pc)(Pc')]) Tb(III) bis(phthalocyaninate) complexes that contain different peripheral substitution patterns (i.e., tert-butyl or tert-butylphenoxy groups) have been synthesized in their neutral radical forms and then reduced into their corresponding anionic forms as stable tetramethylammonium/tetrabutylammonium salts. All of these compounds were spectroscopically characterized and their magnetic susceptibility properties were investigated. As a general trend, the radical forms exhibited larger energy barriers for spin reversal than their corresponding reduced compounds. Remarkably, heteroleptic complexes that contain elect…

Near-Quantitative Internal Quantum Efficiency in a Light-Emitting Electrochemical Cell

A green-light-emitting iridium(III) complex was prepared that has a photoluminescence quantum yield in a thin-film configuration of almost unity. When used in a simple solid-state single-layer light-emitting electrochemical cell, it yielded an external quantum efficiency of nearly 15% and a power efficiency of 38 Lm/W. We argue that these high external efficiencies are only possible if near-quantitative internal electron-to-photon conversion occurs. This shows that the limiting factor for the efficiency of these devices is the photoluminescence quantum yield in a solid film configuration. The observed efficiencies show the prospect of these simple electroluminescent devices for lighting and…

Hybrid Magnetic Materials Based on Nitroxide Free Radicals and Extended Oxalato‐Bridged Bimetallic Networks

A series of hybrid organic-inorganic magnets of formula p-rad[MIICr(ox)3] [M = Mn (1), Co (2), Ni (3), Zn (4)] and m-rad[MIICr(ox)3] [M = Mn (5), Co (6)], in which N-methylpyridinium cations bearing a nitronyl nitroxide moiety in positions 3 (m-rad) or 4 (p-rad) of the pyridine ring coexist with the 2D honeycomb-like oxalato-bridged bimetallic lattice, has been prepared and studied by AC and DC magnetic susceptibility measurements and EPR spectroscopy. In general, the physical properties of these magnets are not altered significantly by the insertion of the nitronyl nitroxide radicals although these paramagnetic molecules seem to interact weakly with the inorganic network as demonstrated by…

Effects of halogen bonding in ferromagnetic chains based on Co(ii) coordination polymers

Two linear cobalt chloride ferromagnetic chains, trans-[CoCl2(3,5-X2py)2] [X = Cl (1), Br (2)], have been prepared and the influence of the halogen bonding on the interchain magnetic interactions has been investigated.

Inside Cover: Exploiting Reaction‐Diffusion Conditions to Trigger Pathway Complexity in the Growth of a MOF (Angew. Chem. Int. Ed. 29/2021)

Modeling the magnetic properties of lanthanide complexes: relationship of the REC parameters with Pauling electronegativity and coordination number

In a previous study, we introduced the Radial Effective Charge (REC) model to study the magnetic properties of lanthanide single ion magnets. Now, we perform an empirical determination of the effective charges (Zi) and radial displacements (Dr) of this model using spectroscopic data. This systematic study allows us to relate Dr and Zi with chemical factors such as the coordination number and the electronegativities of the metal and the donor atoms. This strategy is being used to drastically reduce the number of free parameters in the modeling of the magnetic and spectroscopic properties of f-element complexes. SPINMOL FP7-ERC-247384 ERC-CoG-647301 DECRESIM MAT2011-22785 MAT2014-56143-R CTQ2…

Ferrimagnetic Heisenberg chain; influence of a random exchange interaction

We report on the magnetic behavior of ‘‘rigid’’ ferrimagnetic chains isolated in bimetallic complexes of the EDTA and ‘‘flexible’’ ones obtained in the amorphous variety. As shown by LAXS, the only noteworthy difference in the amorphous state is the random distribution of bond angles between nearest neighbors within chains. The ‘‘rigid’’ bimetallic chains in CoNi(EDTA)6H2O are described in terms of Heisenberg model with an exchange coupling J=−7.5 K. The behavior of the amorphous variety somewhat differs, following the law X=AT−0.8 typical of REHAC. A classical spin chain model involving a J distribution and alternating g factors allows to explain successfully the temperature dependence of …

Oxalate-Based Soluble 2D Magnets: The Series [K(18-crown-6)]3[MII3(H2O)4{MIII(ox)3}3] (MIII = Cr, Fe; MII = Mn, Fe, Ni, Co, Cu; ox = C2O42−; 18-crown-6 = C12H24O6)

The synthesis and magnetic properties of the oxalate-based molecular soluble magnets with general formula [K(18-crown-6)] 3[M (II) 3(H 2O) 4{M (III)(ox) 3} 3] (M (III) = Cr, Fe; M (II) = Mn, Fe, Ni, Co, Cu; ox = C 2O 4 (2-)) are here described. All the reported compounds are isostructural and built up by 2D bimetallic networks formed by alternating M (III) and M (II) ions connected through oxalate anions. Whereas the Cr (III)M (II) derivatives behave as ferromagnets with critical temperatures up to 8 K, the Fe (III)M (II) present ferri- or weak ferromagnetic ordering up to 26 K.

Influence of the pH on the synthesis of reduced graphene oxide under hydrothermal conditions

Here we describe the important role played by the pH on the morphology and structure of the reduced graphite oxide (rGO) samples obtained by hydrothermal treatment of the previously prepared GO. The nature of the resulting samples has been studied on the basis of a complete battery of experimental techniques.

A fluorinated 2D magnetic coordination polymer

Herein we show the versatility of coordination chemistry to design and expand a family of 2D materials by incorporating F groups at the surface of the layers. Through the use of a prefuntionalized organic linker with F groups, it is possible to achieve a layered magnetic material based on Fe(ii) centers that are chemically stable in open air, contrary to the known 2D inorganic magnetic materials. The high quality of the single crystals and their robustness allow to fabricate 2D molecular materials by micromechanical exfoliation, preserving the crystalline nature of these layers together with the desired functionalization.

Enhancing Light Emission in Interface Engineered Spin-OLEDs through Spin-Polarized Injection at High Voltages

The quest for a spin-polarized organic light-emitting diode (spin-OLED) is a common goal in the emerging fields of molecular electronics and spintronics. In this device, two ferromagnetic (FM) electrodes are used to enhance the electroluminescence intensity of the OLED through a magnetic control of the spin polarization of the injected carriers. The major difficulty is that the driving voltage of an OLED device exceeds a few volts, while spin injection in organic materials is only efficient at low voltages. The fabrication of a spin-OLED that uses a conjugated polymer as bipolar spin collector layer and ferromagnetic electrodes is reported here. Through a careful engineering of the organic/…

Manipulation of the spin in single molecule magnets via Landau-Zener transitions

We theoretically investigate the effects of a magnetic pulse on a single-molecule magnet (SMM) initially magnetized by a dc field along the easy axis of magnetization. In the Landau\char21{}Zener (LZ) scheme, it is shown that the final spin state is a function of the shape and duration of the pulse, conditioned by the decoherence time of the SMM. In the case of coherent tunneling, the asymmetric pulses are shown to reverse the direction of the magnetization, while the symmetric pulses can only decrease the value of the initial magnetization. It is also demonstrated that the application of an external variable dc field in the hard plane of magnetization provides the possibility to tune the r…

Insertion of a [Fe II (pyimH) 3 ] 2+ [pyimH = 2‐(1 H ‐Imidazol‐2‐yl)pyridine] Spin‐Crossover Complex Inside a Ferromagnetic Lattice Based on a Chiral 3D Bimetallic Ox­alate Network

The insertion of the [FeII(pyimH)3]2+ [pyimH = 2-(1H-imidazol-2-yl)pyridine] spin-crossover complex into a ferromagnetic bimetallic oxalate network affords the hybrid compound [FeII(pyimH)3][MnIICrIII(ox)3]2·X (ox = C2O42–). This spin-crossover complex templates the growth of crystals formed by a chiral 3D oxalate network. The magnetic properties of this hybrid magnet show the coexistence of long-range ferromagnetic ordering at 4.5 K and a spin crossover of the intercalated [FeII(pyimH)3]2+ complex above 250 K. The compound presents a light-induced excited spin-state trapping (LIESST) effect below 60 K although with limited photoconversion (less than 8 %).

Spontaneous Magnetization in Ni−Al and Ni−Fe Layered Double Hydroxides

Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetizati…

Phase Transitions in Spin-Crossover Thin Films Probed by Graphene Transport Measurements

Future multi-functional hybrid devices might combine switchable molecules and 2D material-based devices. Spin-crossover compounds are of particular interest in this context since they exhibit bistability and memory effects at room temperature while responding to numerous external stimuli. Atomically-thin 2D materials such as graphene attract a lot of attention for their fascinating electrical, optical, and mechanical properties, but also for their reliability for room-temperature operations. Here, we demonstrate that thermally-induced spin-state switching of spin-crossover nanoparticle thin films can be monitored through the electrical transport properties of graphene lying underneath the f…

Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2H−TaS2

International audience; The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides 2H−TaS2 is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density wave is found to collapse at 8.5 GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5 GPa. Our report constitutes a new observation of such Raman active Higgs mode si…

Langmuir-Blodgett Films of Magnetic Clusters

Abstract The mixed-valence manganese clusters [Mn12O12(carboxylato)16] have been organized in a multilayer architecture. Indeed, well-defined Langmuir-Blodgett (LB) films of the acetate and the benzoate Mn12 clusters can be obtained using behenic acid as organic matrix. Here, we report the magnetic properties of these multilayers, which present a marked hysteresis at 2 K.

Phosphorescent hybrid organic-inorganic light-emitting diodes.

Molecular stabilization of chemically exfoliated bare MnPS3 layers

Transition metal chalcogenophosphates of general formula MPX3 have attracted recent interest in the field of 2D materials due to the possibility of tuning their properties when reaching the 2D limit. Several works address this challenge by dry mechanical exfoliation. However, only a few of them use a scalable approach. In this work, we apply a general chemical protocol to exfoliate MnPS3. The method uses in a first step chemical intercalation and liquid phase exfoliation, followed in a second step by the addition of molecules used as capping agents on the inorganic layers. Therefore, molecules of different nature prompts the quality of the exfoliated material and its stabilization in aqueou…

A hybrid magnet with coexistence of ferromagnetism and photoinduced Fe(iii) spin-crossover

International audience; The insertion of a [Fe(sal2-trien)]+ complex cation into a 2D oxalate network results in a hybrid magnet with coexistence of magnetic ordering and photoinduced spin-crossover (LIESST effect) in compound [FeIII(sal2-trien)][MnIICrIII(ox)3]*(CH2Cl2) (1). A complete photomagnetic characterization together with a detailed structural analysis of the low-spin (LS) and high-spin (HS) structures of 1 is presented in order to understand such unusual behavior. This very rare and unexpected property in a FeIII spin-crossover complex, has been attributed to the strong distortion exhibited by the metastable HS state. Furthermore, 1 has shown that, in contrast to what has been pre…

Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt Clusters

Five Co(II) silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K(20)[{(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)}(2)Co(H(2)O)(2)]47 H(2)O (1) consists of two {(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)} units connected by a {CoO(4)(H(2)O)(2)} group. In the chiral species K(7)[Co(1.5)(H(2)O)(7))][(gamma-SiW(10)O(36))(beta-SiW(8)O(30)(OH))Co(4)(OH)(H(2)O)(7)]36 H(2)O (2), a {gamma-SiW(10)O(36)} and a {beta-SiW(8)O(30)(OH)} unit enclose a mononuclear {CoO(4)(H(2)O)(2)} group and a {Co(3)O(7)(OH)(H(2)O)(5)} fragment. The two trinuclear Co(II) clusters present in 1 enclose a mu(4)-O atom, while in 2 a mu(3)-OH bridging group co…

Two pyrazolylborate dysprosium(III) and neodymium(III) single ion magnets modeled by a Radial Effective Charge approach

Abstract A Radial Effective Charge model based on a point charge approach is applied in order to study the magnetic behavior of two lanthanoid single ion magnets coordinated by pyrazole-based ligands that produce a D3h crystal field. We obtain the lowest-lying magnetic levels and the associated wave functions of Dy(H2BPzMe22)3 (1), and the tricapped NdTp3 (2), where H2BPzMe22 = dihydrobis(dimenthylpyrazolyl)borate and Tp = trispyrazolylborate. Results support the observed SMM behavior.

Hybrid Molecular Materials Based upon the Photochromic Nitroprusside Complex, [Fe(CN)5NO]2-, and Organic π-Electron Donors. Synthesis, Structure, and Properties of the Radical Salt (TTF)7[Fe(CN)5NO]2 (TTF = Tetrathiafulvalene)

An organic/inorganic hybrid salt is obtained by combination of the photochromic nitroprusside complex with the organic donor TTF. The organic part shows an unprecedented 2D organization formed by an orthogonal arrangement of TTF hexamers and monomers. However, the donor layers are formed by pairs of moderately interacting dimeric (TTF)22+ units surrounded by neutral TTF molecules in such a way that the charge is localized and the compound is a semiconductor. Short contacts between the organic layers and the nitroprusside anions are present that may affect the photophysical properties of the nitroprusside.

Redox and guest tunable spin-crossover properties in a polymeric polyoxometalate

A bifunctionalized polyoxometalate (POM), [V6O19(C16H15N6O)2]2−, which contains a redox active hexavanadate moiety covalently linked to two tridentate 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligands, has been prepared and characterized. Reaction of this hybrid molecule with Fe(II) or Zn(II) ions produces crystalline neutral 1D networks of formula Fe[V6O19(C16H15N6O)2]·solv (2) and Zn[V6O19(C16H15N6O)2]·solv (3) (solv = solvent molecules). Magnetic properties of 2 show an abrupt spin-crossover (SCO) with the temperature, which can be induced by light irradiation at 10 K (Light-Induced Excited Spin-State Trapping, LIESST effect). Interestingly, this porous and flexible structure enables reversi…

Electric field control of the spin state in mixed-valence magnetic molecules.

Multiferroic molecules for spintronics: In a many-electron mixed-valence dimer with dominant double exchange, as compared with antiferromagnetic superexchange, the electric field is shown to induce a spin crossover from the ferromagnetic spin state to the antiferromagnetic one. This leads to a sharp decrease in the magnetic moment of the molecule and a simultaneous stepwise increase in the electric dipole (see figure).

Single-Molecule Magnets: Electrostatic Anchoring of Mn4 Single-Molecule Magnets onto Chemically Modified Multiwalled Carbon Nanotubes (Adv. Funct. Mater. 5/2012)

Oxalate‐Based 3D Chiral Magnets: The Series [Z II (bpy) 3 ][ClO 4 ][M II Fe III (ox) 3 ] (Z II = Fe, Ru; M II = Mn, Fe; bpy = 2,2'‐Bipyridine; ox = Oxalate Dianion)

The synthesis, structure, and physical properties of the oxalate-based molecular magnets with the formula [ZII(bpy)3][ClO4][MIIFeIII(ox)3] (ZII = Fe, Ru; MII = Mn, Fe; bpy = 2,2'-bipyridine; ox = oxalate dianion) are presented here. All compounds are isostructural and crystallize in the chiral cubic space group P4132, and contain three-dimensional dimetallic networks formed by alternating MII and MIII ions that are connected by oxalate anions. These compounds exhibit strong antiferromagnetic interactions that give rise to magnetic ordering as ferrimagnets or weak ferromagnets, with critical temperatures of up to 20 K, which is twice as high as those found for the isostructural magnets based…

Multifunctional molecular materials

2D and 3D bimetallic oxalate-based ferromagnets prepared by insertion of different FeIII spin crossover complexes

The syntheses, structures and magnetic properties of the compounds of formula [Fe(III)(5-NO(2)sal(2)-trien)][Mn(II)Cr(III)(ox)(3)]·CH(3)NO(2).0.5H(2)O (1) and [Fe(III)(5-CH(3)Osal(2)-trien)][Mn(II)Cr(III)(ox)(3)] (2) are reported. The structure of 1, that crystallizes in the P2(1) chiral space group, presents a 2D honeycomb anionic layer formed by Mn(II) and Cr(III) ions linked through oxalate ligands and a cationic layer of [Fe(III)(5-NO(2)sal(2)-trien)](+) complexes intercalated between the 2D oxalate network. The structure of 2, that crystallizes in the Pna2(1) acentric space group, presents a 3D achiral anionic network formed by Mn(II) and Cr(III) ions linked through oxalate ligands wit…

Semiclassical approximation in the magnetic problem of exchange-coupled mixed valence clusters

Abstract The frameworks of the applicability of the semiclassical adiabatic approach suggested by Borras-Almenar, Coronado and Tsukerblat to the magnetic problem of mixed valence clusters are considered in a model taking into account magnetic exchange, double exchange and vibronic interaction. The results for the quantum-mechanical and semicalssical calculation of the temperature-variable magnetic moments are compared with those within the scope of the semiclassical approximation for the dimeric d 1 —d 2 clusters and trimeric d 1 —d 1 —d 2 systems with partial delocalization over a pair of ions. The semiclassical approach describes with high accuracy the temperature dependencies of the magn…

A Mononuclear Uranium(IV) Single-Molecule Magnet with an Azobenzene Radical Ligand

A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3‐tacn}UIV(η2‐N2Ph2.)] (2), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3‐tacn}] (1). Compound 2 was characterized by single‐crystal X‐ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approxim…

Charge transfer salts of tetrathiafulvalene derivatives with magnetic iron(III) oxalate complexes: [TTF]7[Fe(ox)3]2·4H2O, [TTF]5[Fe2(ox)5]·2PhMe·2H2O and [TMTTF]4[Fe2(ox)5]· PhCN·4H2O (TMTTF = tetramethyltetrathiafulvalene) †

Three novel TTF (tetrathiafulvalene) and TMTTF (tetramethyltetrathiafulvalene) radical salts of monomeric and dimeric iron(III) oxalate magnetic complexes, [TTF]7[Fe(ox)3]2·4H2O 1, [TTF]5[Fe2(ox)5]·2PhMe·2H2O 2 and [TMTTF]4[Fe2(ox)5]·PhCN·4H2O 3, have been synthesized, and their structures and physical properties investigated. The structures for these semiconducting salts feature monodimensional stackings of the radical cations interleaved by the complexes [Fe(ox)3]3− and [Fe2(ox)5]4−, and solvent molecules. For the novel dinuclear complex [Fe2(ox)5]4− antiferromagnetic exchange between the two iron atoms through the oxalate bridge was found.

A New Heptanuclear Cobalt(II) Cluster Encapsulated in a Novel Heteropolyoxometalate Topology:  Synthesis, Structure, and Magnetic Properties of [Co7(H2O)2(OH)2P2W25O94]16-

The synthesis and the structural and magnetic characterization of a novel heptanuclear cobalt cluster encapsulated in a heteropolyoxotungstate is reported. This complex shows how it is possible to control the nuclearity of the Co clusters formed in a tungstate solution by slightly changing the synthetic conditions, and the relevance of pH in this regard. This heptanuclear complex [Co7(H2O)2(OH)2P2W25O94]16- (Co7) crystallizes in the triclinic space group P1 (a = 12.3403(6) A, b = 22.5966(11) A, c = 23.2645(12) A, α = 68.7830(11)°, β = 83.7981(12)°, γ = 78.5423(13)°, V = 5922.4(5) A3, Z = 2) and is formed by six CoO6 octahedra from two Co3 trimers sustained by Keggin trivacant fragments held…

Long-Living Light-Emitting Electrochemical Cells - Control through Supramolecular Interactions

Light-emitting electrochemical cells with lifetimes surpassing 3000 hours at an average luminance of 200 cd m(-2) are obtained with an ionic iridium(III) complex conveniently designed to form a supramolecularly caged structure.

Magnetism in Polyoxometalates: Anisotropic Exchange Interactions in the Co Moiety of [Co3W(D2O)2(ZnW9O34)2]12−—A Magnetic and Inelastic Neutron Scattering Study

The ground-state properties of a Co moiety encapsulated in a polyoxometalate anion were investigated by combining measurements of specific heat, magnetic susceptibility, and low-temperature magnetization with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na12[Co3W(D2O)2(ZnW9O34)2]⋅40 D2O (Co3). The ferromagnetic Co3O14 cluster core consists of three octahedrally oxo-coordinated CoII ions. According to the single-ion anisotropy and spin–orbit coupling of the octahedral CoII ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co3 spin cluster is anisotropic and is expressed as ℋ=−2Σ(JŜ1αŜ2α+JŜ2αŜ3α), w…

Magnetic clusters from polyoxometalate complexes

Abstract The present article highlights the increasing interest of polyoxometalates in molecular magnetism, providing at the same time a perspective of the state-of-the-art in this area. The main focus is the polyoxotungstates. The first aspect we discuss is that of the coordination chemistry of these metal–oxide ligands. We show that this chemistry leads to remarkable examples of well-insulated magnetic clusters of controlled nuclearity and topology. In these clusters detailed information on the nature of the magnetic exchange interactions can be extracted by using, in addition to the classical magnetic techniques (magnetic susceptibility, magnetization and EPR spectroscopy), other physica…

WS 2 /MoS 2 Heterostructures through Thermal Treatment of MoS 2 Layers Electrostatically Functionalized with W 3 S 4 Molecular Clusters

The preparation of 2D stacked layers combining flakes of different nature gives rise to countless numbers of heterostructures where new band alignments, defined at the interfaces, control the electronic properties of the system. Among the large family of 2D/2D heterostructures, the one formed by the combination of the most common semiconducting transition metal dichalcogenides, WS2 /MoS2 , has awakened great interest owing to its photovoltaic and photoelectrochemical properties. Solution as well as dry physical methods have been developed to optimize the synthesis of these heterostructures. Here, a suspension of negatively charged MoS2 flakes is mixed with a methanolic solution of a cationi…

Multifuctionality in Molecular Conductors and Magnets

Building multifuntionality in a material is a hot focus of research in contemporary materials science. Molecule-based materials offer unique opportunities in this context since the versatility of molecular chemistry provides the possibility to design materials that combine in the same crystal lattice two or more solid-state properties such as ferromagnetism, conductivity, superconductivity or non-linear optics. This opens new possibilities for potential applications in molecular electronics. A possible approach to reach this goal consists of building up hybrid solids formed by two molecular networks, such as anion/cation salts or host/guest solids, where each network furnishes distinct prop…

Tuning the magneto-structural properties of non-porous coordination polymers by HCl chemisorption.

Responsive materials for which physical or chemical properties can be tuned by applying an external stimulus are attracting considerable interest in view of their potential applications as chemical switches or molecular sensors. A potential source of such materials is metal-organic frameworks. These porous coordination polymers permit the physisorption of guest molecules that can provoke subtle changes in their porous structure, thus affecting their physical properties. Here we show that the chemisorption of gaseous HCl molecules by a non-porous one-dimensional coordination polymer instigates drastic modifications in the magnetic properties of the material. These changes result from profoun…

ChemInform Abstract: Magnetic Properties of NiIICrIIILayered Double Hydroxide Materials.

This paper describes the isolation of four layered double hydroxide (LDH) compounds having the general formula[NiII3–xCrIIIx(OH)6](CO3)x/2·yH2O [x = 0.57 (1), 0.69 (2), 0.81 (3) and 0.93 (4)] by using homogeneous precipitation methods and varying the metal ratio in the synthetic solutions. All the reported compounds have carbonate anions in the interlamellar space. This fact forces the interlayer distances to remain unchanged in all the cases, thus providing an ideal system in which the changes observed in magnetic properties can be correlated with metal composition along the hydroxide layers.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis, crystal structure and magnetic properties of [Cr2Cu2(bpy)4(ox)5]·2H2O. An oxalato-bridged heterometallic tetramer

A new heterometallic tetramer of formula [Cr2Cu 2(bpy)4(ox)5]·2H2O (1) (bpy=2,2′-bipyridine; ox=oxalate dianion) has been prepared and characterised by single-crystal X-ray diffraction, magnetic susceptibility measurements and ESR spectroscopy. The tetranuclear unit in 1 can be viewed as the combination of two terminal [Cr(bpy)2(ox)]- units with a central oxalato-bridged copper(II) dimer. The chromium ions are in a distorted octahedral environment with metal-ligand distances ranging from 1.944(4) to 2.064(5) A. The copper(II) centres lie in an axially distorted octahedron. The axial positions are occupied by one oxygen atom belonging to the central bridging oxalate anion [O(9)-Cu(1): 2.245(…

Increasing the Coercivity in Layered Molecular-based Magnets A[MIIMIII(ox)3] (MII = Mn, Fe, Co, Ni, Cu; MIII = Cr, Fe; ox = oxalate; A = organic or organometallic cation)

Effect of nanostructuration on the spin crossover transition in crystalline ultrathin films† †Electronic supplementary information (ESI) available: Materials and methods, supplementary figures and tables. See DOI: 10.1039/c8sc04935a

Film thickness and microstructure critically affect the spin crossover transition of a 2D coordination polymer.

Magnetic transition metal complexes of tetrathiafulvalene (TTF) derivatives

We have prepared and characterized the transition metal complexes of two different TTF derivatives. We have oxidized the different complexes with electrooxidation and chemical oxidation techniques and the results are discussed. The magnetic properties of the complexes have been studied. TTF-carboxylate chelates are not stable enough, but thioether-TTF shows promising charge transfer salts.

Polyoxometalate Monolayers in Langmuir-Blodgett Films

Langmuir and Langmuir-Blodgett (LB) films of a variety of polyoxometalates of different shapes, sizes, and charges were prepared by taking advantage of the adsorption properties of these polyanions on a positively charged monolayer of an organic surfactant spread on water. Three different aspects were investigated. 1) The electrochemical and electrochromic properties of LB films containing the easily reducible polyoxoanion [P2Mo18O62]6-. Absorbance changes of these LB films deposited onto an ITO substrate have been induced by repeated switching of the applied potential. These changes are due to the formation of the colored reduced forms of the polyanion. Coloration and bleaching of the LB f…

1D ferrimagnetism in homometallic chains

The magnetic properties of the cobalt zigzag chain Co(bpy)(NCS)2 (bpy=2,2′‐bipyridine) are discussed on the basis of an Ising‐chain model that takes into account alternating Landé factors. It is emphasized, for the first time, that a homometallic chain containing only one type of site can give rise to a 1D ferrimagneticlike behavior. Juan.J.Borras@uv.es , Eugenio.Coronado@uv.es

Magnetic properties of the layered lanthanide hydroxide series Y(x)Dy(8-x)(OH)20Cl4·6H2O: from single ion magnets to 2D and 3D interaction effects.

The magnetic properties of layered dysprosium hydroxides, both diluted in the diamagnetic yttrium analogous matrix (LYH:0.04Dy), and intercalated with 2,6-naphthalene dicarboxylate anions (LDyH-2,6-NDC), were studied and compared with the recently reported undiluted compound (LDyH = Dy8(OH)20Cl4·6H2O). The Y diluted compound reveals a single-molecule magnet (SMM) behavior of single Dy ions, with two distinct slow relaxation processes of the magnetization at low temperatures associated with the two main types of Dy sites, 8- and 9-fold coordinated. Only one relaxation process is observed in both undiluted LDyH and intercalated compounds as a consequence of dominant ferromagnetic Dy-Dy intera…

Mononuclear Lanthanide Complexes: Use of the Crystal Field Theory to Design Single-Ion Magnets and Spin Qubits

Molecular Materials Combining Magnetic and Conducting Properties

Downsizing of robust Fe-triazole@SiO2 spin-crossover nanoparticles with ultrathin shells

A chemical protocol to design robust hybrid [Fe(Htrz)2(trz)](BF4)@SiO2 nanoparticles (NPs) with sizes as small as 28 nm and ultrathin silica shells below 3 nm has been developed. These NPs present a characteristic abrupt spin transition with a subsequent decrease in the width of the thermal hysteresis upon reducing the NP size.

Design of Low-Dimensional Ferrimagnetic Compounds: New Magnetic Lattices in the “EDTA-Family”

The ability of EDTA to wrap around one metal atom (M′) while still providing bridging carboxylate groups to a second atom (M) is the basis for the obtainment of a wide variety of low-dimensional bimetallic ordered systems.

WS 2 /MoS 2 Heterostructures through Thermal Treatment of MoS 2 Layers Electrostatically Functionalized with W 3 S 4 Molecular Clusters

Exchange Interactions I: Mechanisms

A most important phenomenon in molecular magnetism is the exchange interaction between magnetic centers. Its relevance as well as the terms and concepts required to its rationalization were stated long ago by physicists working in the quantum-mechanical theory of magnetism (Heisenberg, Dirac, van Vleck, Anderson, Zener, and many others). Depending on the extent of delocalization of the magnetic moments and on the metallic/non-metallic properties of the solid four kinds of exchange coupling were usually distinguished in the physical literature namely direct exchange, superexchange, indirect exchange and itinerant exchange [1]. The relations of these types of couplings are depicted in Figure …

Multifunctionality in hybrid magnetic materials based on bimetallic oxalate complexes.

This tutorial review illustrates the design of multifunctional oxalate-based magnetic materials through the combination of the intrinsic magnetism of the metal–organic framework and the additional properties introduced by several organic/inorganic functional cations.

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Layered double hydroxides (LDHs) are low dimensional materials that act as benchmark catalysts for the oxygen evolution reaction (OER). Many LDH properties affecting the OER have been studied to reach the optimal efficiency but no systematic studies concerning the influence of the interlayer space have been developed. In this context, these materials allow a large tunability in their chemical composition enabling the substitution of the interlayer anion and therefore modifying exclusively the basal space. Here, we synthesize by anion exchange reactions a surfactantintercalated family of NiFe-LDHs with increasing basal spacing ranging from 8.0 to 31.6 Å (one of the largest reported so far fo…

Electrically switchable magnetic exchange in the vibronic model of linear mixed valence triferrocenium complex

In this article, we report our development of a vibronic model for the electric-field control of antiferromagnetic superexchange in the mixed-valence (MV) triferrocenium complex FeIII-FeII-FeIII proposed as a possible candidate for the molecular implementation of a quantum logic gate. Along with the electronic interactions, such as electron transfer between the iron ions in different oxidation degrees and Coulomb repulsion of the extra holes, the proposed model of the triferrocenium complex also takes into account the vibronic coupling as an inherent ingredient of the problem of mixed valency. The latter is described by the conventional Piepho-Krauzs-Shatz (PKS) model adapted to the linear …

Fast Pirouetting Motion in a Pyridine Bisamine-Containing Copper-Complexed Rotaxane

The present work reports the introduction of pyridine bisamine terdentate ligands in the structure of a pirouetting copper rotaxane. Rotaxane 2[PF6] constitutes the first example of the incorporation of imine-based dynamic covalent chemistry in the synthesis of switchable copper-complexed interlocked systems. In this rotaxane, the substitution of the classical terpyridine terdentate unit by a pyridine bisamine moiety has led to a significant stabilization of the pentacoordinated site. That fact has been evidenced by EPR spectroscopy and cyclic voltammetry. Regarding the tetracoordinated site, the congestion around the coordination sphere has been reduced to accelerate the typically slow reo…

One-Dimensional Magnetism: An Overview of the Models

Two hybrid organometallic-inorganic layered magnets from the series [ ZIIICp*2] [ MIIMIII(ox)3] studied with μ+SR

We present zero-field muon spin relaxation (ZF-μ + SR) measurements on two examples of a new series of hybrid organometallic-inorganic layered magnets, namely ferromagnetic [FeCp* 2 ][MnCr(ox) 3 ] and ferrimagnetic [CoCp* 2 ][FeFe(ox) 3 ] (where ox = oxalate and Cp* = pentame- thyl-cyclopentadienyl). Both materials show multi-component muon spin precession signals characteristic of quasistatic magnetic fields at several distinct muon sites. The temperature dependence of the precession frequencies allow critical exponents to be extracted. Possible muon sites are discussed on the basis of dipole field calculations.

The Missing Link in the Magnetism of Hybrid Cobalt Layered Hydroxides: The Odd‐Even Effect of the Organic Spacer

A dramatic change in the magnetic behaviour, which solely depends on the parity of the organic linker molecules, has been found in a family of layered CoII hydroxides covalently functionalized with dicarboxylic molecules. These layered hybrid materials have been synthesized at room temperature using a one-pot procedure through the epoxide route. While hybrids connected by odd alkyl chains exhibit coercive fields (Hc) below ca. 3500 Oe and show spontaneous magnetization at temperatures (TM) below 20 K, hybrids functionalized with even alkyl chains behave as hard magnets with Hc>5500 Oe and display a TM higher than 55 K. This intriguing behaviour was studied by density functional theory with …

White Light-Emitting Electrochemical Cells Based on the Langmuir–Blodgett Technique

Light-emitting electrochemical cells (LECs) showing a white emission have been prepared with Langmuir-Blodgett (LB) films of the metallosurfactant bis[2-(2,4-difluorophenyl)pyridine][2-(1-hexadecyl-1H-1,2,3-triazol-4-yl)pyridine]iridium(III) chloride (1), which work with an air-stable Al electrode. They were prepared by depositing a LB film of 1 on top of a layer of poly(N,N'-diphenyl-N,N'-bis(4-hexylphenyl)-[1,1'-biphenyl]-4,4'-diamine (pTPD) spin-coated on indium tin oxide (ITO). The white color of the electroluminescence of the device contrasts with the blue color of the photoluminescence of 1 in solution and within the LB films. Furthermore, the crystal structure of 1 is reported togeth…

Dual-Emissive Photoluminescent Langmuir−Blodgett Films of Decatungstoeuropate and an Amphiphilic Iridium Complex

Langmuir monolayers and Langmuir-Blodgett (LB) films of the decatungstoeuropate [Eu(W(5)O(18))(2)](9-) (EuW(10)) and the amphiphilic Ir complex 1 have been successfully fabricated by using the adsorption properties of the EuW(10) polyanion dissolved in the aqueous subphase onto a positively charged 1 monolayer at the air-water interface. The compression isotherms and Brewster angle microscopy (BAM) of monolayers of 1 on pure water (1 monolayer) and on a subphase containing 10(-6) M EuW(10) and 10(-3) M NaCl (1/EuW(10) monolayer) have been studied. Infrared and UV-vis spectroscopy of the transferred LB films indicate that EuW(10) and 1 molecules are incorporated within these LB films. X-ray …

Room Temperature Magnetism in Layered Double Hydroxides due to Magnetic Nanoparticles

Some recent reports claiming room temperature spontaneous magnetization in layered double hydroxides (LDHs) have been published; however, the reported materials cause serious concern as to whether this cooperative magnetic behavior comes from extrinsic sources, such as spinel iron oxide nanoparticles. The syntheses of crystalline Fe(3+)-based LDHs with and without impurities have been developed, highlighting the care that must be taken during the synthetic process in order to avoid misidentification of magnetic LDHs.

New coordination polymers based on a novel polynitrile ligand: Synthesis, structure and magnetic properties of the series [M(tcnoetOH)2(4,4′-bpy)(H2O)2] (tcnoetOH−=[(NC)2CC(OCH2CH2OH)C(CN)2]−; M=Fe, Co and Ni)

International audience; A novel polynitrile anionic ligand, tcnoetOH−(=[(NC)2CC(OCH2CH2OH)C(CN)2]−), has been synthesized by a one-pot reaction from a cyclic acetal and malononitrile. This ligand has been successfully used to prepare, with 4,4′-bpy as co-ligand, a novel series of coordination polymers formulated as [M(tcnoetOH)2(4,4′-bpy)(H2O)2] with M(II) = Fe (1), Co (2) and Ni (3). These isostructural compounds present a linear chain structure consisting of octahedrally coordinated metal ions bridged by trans 4,4′-bpy ligands. The coordination sphere of the metal ions is completed with two terminal tcnoetOH− ligand and two water molecules. The magnetic properties indicate that the three …

Synthesis and characterisation of polymeric manganese and zinc 5-hydroxyisophthalates

Abstract The crystallisation of 5-hydroxyisophthalic acid with divalent Mn or with Mn or Zn and either 2,2-bipyridine (2,2-bipy) or pyridine-2-(1H-pyrazol-3-yl) gave solids of composition [Mn(C8H4O5)(H2O)3]·2H2O (1), [Mn(C8H4O5)(2,2′-bipy)]·H2O (2), [Mn2(C8H4O5)2(C8H7N3)2]·H2O (3) and [Zn(C8H4O5)(2,2′-bipy)] (4). Each compound has 1D co-ordinative chains that are connected by hydrogen bonds. Compounds 2–4 contain M2C2O4 rings with pseudo-chair geometries. The Mn atoms in 2 are coupled antiferromagnetically.

Illustrating the processability of magnetic layered double hydroxides: layer-by-layer assembly of magnetic ultrathin films.

We report the preparation of single-layer layered double hydroxide (LDH) two-dimensional (2D) nanosheets by exfoliation of highly crystalline NiAl-NO3 LDH. Next, these unilamellar moieties have been incorporated layer-by-layer (LbL) into a poly(sodium 4-styrenesulfonate)/LDH nanosheet multilayer ultrathin film (UTF). Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible light (UV-vis), and X-ray diffraction (XRD) profiles have been used to follow the uniform growth of the UTF. The use of a magnetic LDH as the cationic component of the multilayered architecture enables study of the resulting magnetic properties of the UTFs. Our magnetic data show the appearance of spontaneous …

Magnetic–fluorescent Langmuir–Blodgett films of fluorophore-labeled ferritin nanoparticles

Abstract We have covalently coupled fluorophore 4-(2-hydroxyethoxy)-7-nitro-2,1,3-benzoxadiazole (NBD) to the external ferritin shell through lysine residues. An increase in the luminescence quantum yield of the fluorescent ferritin particles and a blue shift in its emission peak compared to individual fluorophore were observed. The study of the particles by transmission electron microscopy showed that the native iron core ferritin is intact and that no degradation occurs during chemical functionalization of the protein shell. The NBD-labeled ferritin particles are water soluble, which allowed their controlled deposition by the Langmuir–Blodgett (LB) technique. Superparamagnetic and fluores…

Metallic Conductivity Down to 2 K in a Polyoxometalate-Containing Radical Salt of BEDO-TTF

Fundamental Insights into the Covalent Silane Functionalization of NiFe Layered Double Hydroxides

Layered double hydroxides (LDHs) are a class of 2D anionic materials exhibiting wide chemical versatility and promising applications in different fields, ranging from catalysis to energy storage and conversion. However, the covalent chemistry of this kind of 2D materials is still barely explored. Herein, the covalent functionalization with silanes of a magnetic NiFe-LDH is reported. The synthetic route consists of a topochemical approach followed by anion exchange reaction with surfactant molecules prior to covalent functionalization with the (3-aminopropyl)triethoxysilane (APTES) molecules. The functionalized NiFe-APTES was fully characterized by X-ray diffraction, infrared spectroscopy, e…

Innentitelbild: Exploiting Reaction‐Diffusion Conditions to Trigger Pathway Complexity in the Growth of a MOF (Angew. Chem. 29/2021)

Magnetism and EPR spectra of the two‐sublattice manganese chain Mn2(EDTA)⋅9H2O

We report on the magnetic behavior and single‐crystal EPR spectra of the chain complex Mn2(EDTA)⋅9H2O characterized by two different alternating sites for the manganese ions. Magnetic susceptibility data are indicative of weak antiferromagnetic exchange interactions between the manganese ions, showing a maximum of about 3 K. This behavior can be accurately described on the basis of a Heisenberg chain model that assumes classical spins, giving J/k=−0.72 K and g=2.0. The EPR spectra are typically low dimensional, with an angular dependence of the linewidth of the type (3 cos2 θ−1)n (n=4/3 or 2). Nevertheless, such a behavior cannot be reproduced from a one‐dimensional model with dipolar broad…

Cationic Mn12 Single-Molecule Magnets and Their Polyoxometalate Hybrid Salts

A carboxy-substituted alkylammonium salt, namely, (4-carboxybenzyl)tributylammonium hexafluorophosphate, ZHPF(6), was prepared and used as incoming carboxylate ligand in a ligand-exchange reaction with [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)] (1) to afford a new Mn(12) single-molecule magnet (SMM), [Mn(12)O(12)(Z)(16)(H(2)O)(4)][PF(6)](16) (2), bearing 16 cationic units appended in the periphery. This compound behaves as a single-molecule magnet, exhibiting an out-of-phase ac magnetic susceptibility chi' '(M) signal that shows a single maximum in the 3.1-5.4 K temperature range. The frequency dependence of the maximum follows an Arrhenius law, with an effective energy barrier for reorientati…

High-Quality Metal–Organic Framework Ultrathin Films for Electronically Active Interfaces

Currently available methodologies arguably lack the exquisite control required for producing metal-organic framework (MOF) thin films of sufficient quality for electronic applications. By directing MOF transfer with self-assembled monolayers (SAMs), we achieve very smooth, homogeneous, highly oriented, ultrathin films across millimeter-scale areas that display moderate conductivity likely due to electron hopping. Here, the SAM is key for directing the transfer thereby enlarging the number and nature of the substrates of choice. We have exploited this versatility to evolve from deposition onto standard Si and Au to nonconventional substrates such as ferromagnetic Permalloy. We believe that t…

Switching of Slow Magnetic Relaxation Dynamics in Mononuclear Dysprosium(III) Compounds with Charge Density

The symmetry around a Dy ion is recognized to be a crucial parameter dictating magnetization relaxation dynamics. We prepared two similar square-antiprismatic complexes, [Dy(LOMe)2(H2O)2](PF6) (1) and Dy(LOMe)2(NO3) (2), where LOMe = [CpCo{P(O)(O(CH3))2}3], including either two neutral water molecules (1) or an anionic nitrate ligand (2). We demonstrated that in this case relaxation dynamics is dramatically affected by the introduction of a charged ligand, stabilizing the easy axis of magnetization along the nitrate direction. We also showed that the application of either a direct-current field or chemical dilution effectively stops quantum tunneling in the ground state of 2, thereby increa…

Spontaneous growth of 2D coordination polymers on functionalized ferromagnetic surfaces

2D coordination polymers grow spontaneously on reactive surfaces due to surface oxidation. The growth process is observed in real time.

The Role of Covalent Functionalization in the Thermal Stability and Decomposition of Hybrid Layered Hydroxides

The room temperature synthesis of two Co-based hybrid layered hydroxides containing the same organic ligand (suberate [Sub]), one connected through purely electrostatic interactions (CoAl layered double hydroxide [LDH]), and the other covalently functionalized (α-CoII simonkolleite phase) has been carried out. The magnetic properties exhibit an acute difference in the magnetization temperatures (from ≈10 K for the CoAl-LDH to ≈55 K for the α-CoII). Moreover, the role of the covalent functionalization in the thermal stability and the decomposition has been investigated by a forefront characterization tool consisting of thermogravimetric analysis coupled with gas chromatography and mass spect…

New magnetic conductors and superconductors based on BEDT-TTF and BEDS-TTF

Abstract Here we present our last results in the search for multifunctionality in conducting molecular materials obtained by combining paramagnetic molecular complexes with organic donors to produce paramagnetic molecular metals and superconductors. The structural and physical characterization of two new molecular paramagnetic superconductors ET 4 [H 3 OM(C 2 O 4 ) 3 ].PhBr (M III  = Cr and Fe) are presented (ET = BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene). These salts present a superconductor transition at T c  = 1.5 and 4.0 K, respectively and very anisotropic critical fields H c2a ≈ H c2b ≈0.5 T and H C2C ≈ 8 T for the Fe derivative. We will also present the structural and physica…

Charge Transfer Salts Based on Polyoxometalates and Seleno-Substituted Organic Donors. Synthesis, Structure, and Magnetic Properties of (BEST)3H[PMo12O40]·CH3CN·CH2Cl2 (BEST = Bis(ethylenediseleno)tetrathiafulvalene)

Electrochemical oxidation of the tetrathiafulvalene (TTF) type organic donor bis(ethylenediseleno)tetrathiafulvalene (BEST) in the presence of the Keggin polyoxometalate [PMo12O40]3- affords the radical salt formulated as (BEST)3H[PMo12O40] (crystal data:  triclinic, space group P1 with a = 13.056(1) A, b = 13.957(1) A, c = 22.302(3) A, α = 97.019(9)°, β = 94.17(1)°, γ = 95.847(9)°, and Z = 2). This is the first salt of a selenium-containing donor with a polyoxometalate cluster. The structure of this organic/inorganic hybrid consists of layers of the organic donors that alternate with polyoxometalate layers in the c direction. The organic molecules, which are completely ionized, form two ty…

Electric field controllable magnetic coupling of localized spins mediated by itinerant electrons: a toy model

In this paper, we propose a toy model to describe the magnetic coupling between the localized spins mediated by the itinerant electron in partially delocalized mixed-valence (MV) systems. This minimal model takes into account the key interactions that are common for all such systems, namely, electron transfer in the valence-delocalized moiety and magnetic exchange between the localized spins and the delocalized electrons. The proposed descriptive model is exactly solvable which allows us to qualitatively and quantitatively discuss the main features of the whole class of partially delocalized MV systems. In the case of relatively strong exchange coupling, the combined action of these two int…

Three addressable spin qubits in a molecular single-ion magnet

We show that several qubits can be integrated in a single magnetic ion, using its internal electronic spin states with energies tuned by a suitably chosen molecular environment. This approach is illustrated with a nearly-isotropic Gd(III) ion entrapped in a polyoxometalate molecule. Experiments with microwave technologies, either three dimensional cavities or quantum superconducting circuits, show that this magnetic molecule possesses the number of spin states and the set of coherently addressable transitions connecting these states that are needed to perform a universal three-qubit processor or, equivalently, a d=8-level 'qudit'. Our findings open prospects for developing more sophisticate…

Self-assembly of an iron(ii)-based M5L6 metallosupramolecular cage

A pentanuclear M(5)L(6) coordination cage is self-assembled in solution from a rigid linear heteroditopic phen-tpy ligand and an iron (II) salt.

Catenanes and threaded systems: from solution to surfaces

Functional catenanes and threaded systems able to perform controllable mechanical motions are ideally suited for the design of molecular devices displaying mechanical, electronic, information or sensing functions. These systems have been extensively studied in solution phase and numerous examples of stimuli-driven molecular shuttles have been reported. However, for fully developing their potential applications, they must be interfaced with the macroscopic world. To achieve this objective, in the last few years catenanes and rotaxanes have been organized over surfaces in the form of chemisorbed monolayers or physisorbed monolayers, multilayers and thin films. This tutorial review summarizes …

Attosecond Soft-X-Ray Spectroscopy in a Transition Metal Dichalcogenide

Information about the real-time response of carriers to optical fields is paramount to advance information processing or to understand the bottlenecks of light-matter interaction and energy harvesting. Transition-metal dichalcogenide (TMDC) compounds are an emerging class of materials with attractive structural and electronic properties that can be thinned to the 2D limit and TiS 2 is a paradigmatic example for a semi-metallic TMDC, since its electron mobility ranges between that of a metal and a semiconductor.

Hybrid molecular magnets incorporating organic donors and other electroactive molecules

Molecule-based bidimensional ferromagnets can be used as anionic hosts for electroactive molecules, with the aim of obtaining multiproperty materials exhibiting in addition to the cooperative magnetism other interesting properties according to the nature of the inserted molecules. In particular, hybrid molecular compounds containing conducting (TTF-type organic donors), bi-stable or non-linear optical species are reported.

Heptacoordinated MnIIin oxalate-based bimetallic 2D magnets: synthesis and characterisation of [Mn(L)6][Mn(CH3OH)MIII(ox)3]2(MIII= Cr, Rh; ox = oxalate dianion; L = H2O, CH3OH)

Oxalate-based magnets have been known with several different crystallographic structures, from 1D to 3D, but with all of them based in metal ions with octahedral coordination. In this article we report a new bidimensional oxalate-bridged bimetallic magnet where the divalent metal appears heptacoordinated, which has strong effects in the structure and properties of this materials.

Spin switching in electronic devices based on 2D assemblies of spin-crossover nanoparticles

In this communication we study the transport properties of two-dimensional assemblies of [Fe(Htrz)2(trz)](BF4) spin-crossover nanoparticles (NPs) with two different morphologies. The NPs have been synthesized made in a similar manner than in our previous study in which single NPs were measured. We prepared free-standing self-assembled monolayer sheets of both SCO NPs formed at the air/liquid interface on holey carbon TEM grids to extract their global arrangement and NP size distributions by STEM-HAADF technique. The SCO NP systems present a rod-like shape and possess two different volumes, corresponding to lengths of 25 nm and 44 nm along the rod direction and average diameters of 10 nm and…

Hybrid magnetic superconductors formed by TaS2 layers and spin crossover complexes.

The restacking of charged TaS2 nanosheets with molecular counterparts has so far allowed for the combination of superconductivity with a manifold of other molecule-intrinsic properties. Yet, a hybrid compound that blends superconductivity with spin crossover switching has still not been reported. Here we continue to exploit the solid-state/molecule-based hybrid approach for the synthesis of a layered TaS2-based material that hosts Fe(2+) complexes with a spin switching behavior. The chemical design and synthetic aspects of the exfoliation/restacking approach are discussed, highlighting how the material can be conveniently obtained in the form of highly oriented easy-to-handle flakes. Finall…

Magnetic Nanocomposites Formed by FeNi3 Nanoparticles Embedded in Graphene. Application as Supercapacitors

A general family of magnetic nanocomposites formed by FeNi3 ferromagnetic nanoparticles (NPs) embedded in a graphitized carbon matrix is reported. The soft chemical approach used relies on the catalytic effect of the NPs resulting from the thermal decomposition of the layered double hydroxide precursor, which acts as a multilayered nanoreactor enabling the formation of a range of carbon nanoforms (CNFs). This is followed by acid treatment of the as-prepared nanocomposites to isolate the different CNFs formed. These range from carbon nano-onions to graphene depending on the temperature of the thermal decomposition. This synthetic process paves the way for the rational design of metal–carbon …

Hybrid magnetic/superconducting materials obtained by insertion of a single-molecule magnet into TaS2 layers

et al.

Insertion of Magnetic Bimetallic Oxalate Complexes into Layered Double Hydroxides

Bimetallic oxalate complexes have been successfully inserted into layered double hydroxides as ferromagnetic oxalate-bridged oligomers. Different preparation methods afford different sizes and compositions for the oligomers. In all cases, no magnetic ordering has been observed above 2 K.

Layered ferromagnets hosting tetraalkylammonium-substituted nitronyl nitroxide free radicals

This paper describes the structural, magnetic and EPR properties of hybrid organic/inorganic magnets formed by anionic heterometallic oxalato-based layers and cationic nitronyl nitroxide (NN) free radicals of the tetraalkylammonium type. A series of compounds of formula nBu3NCH2NN[MCr(ox)3] (M = Mn (1), Ni (2), Zn (3)) has been prepared and studied by AC and DC magnetic susceptibility measurements and EPR spectroscopy. Magnetic order with critical temperatures ranging from 5 K to 15 K was confirmed. EPR measurements show that the organic spin carriers interact significantly with the inorganic network.

Materials for molecular electronics and magnetism

Functional molecular materials exhibiting, in particular, electrical, magnetic or optical properties have been an active focus of research over the last 50 years. These materials have been a source of inspiration in two interrelated areas of research, namely, molecular electronics and molecular magnetism, with important implications in biomedical areas. This themed issue highlights recent progress and perspectives in these important areas of materials science. The issue covers topics from the chemical design and manipulation of novel molecular materials with unprecedented control over their properties, even at the single-molecule level, to exciting applications of these special molecular sy…

Hybrid nanostructures based on gold nanoparticles and functional coordination polymers: Chemistry, physics and applications in biomedicine, catalysis and magnetism

During the last decade, the scientific community has become interested in hybrid nanomaterials, especially the ones that combine gold nanoparticles with a second functional component. In this context, coordination polymers are materials that possess potential advantages over conventional inorganic nanomaterials and organic compounds such as chemical versatility, easy processability, high specific area, low toxicity, biodegradability and electronic and magnetic functionalities to name a few. In this manner, the wise integration of Au nanoparticles with coordination polymers in different types of nanostructures has allowed extending the scope of properties and applications of these systems, a…

Toward multifunctional single-molecule magnets: characterization of dodecanuclear manganese complexes by electrospray ionization mass spectrometry.

Single-molecule magnets (SMM) based on the dodecanuclear manganese complexes Mn12O12(RCOO)16 can be readily characterized by electrospray ionization mass spectrometry. This facilitates the synthesis of complex multifunctional molecules that have potential use in the organization of SMM into films or surfaces.

Construction of a General Library for the Rational Design of Nanomagnets and Spin Qubits Based on Mononuclear f-Block Complexes. The Polyoxometalate Case

This paper belongs to a series of contributions aiming at establishing a general library that helps in the description of the crystal field (CF) effect of any ligand on the splitting of the J ground states of mononuclear f-element complexes. Here, the effective parameters associated with the oxo ligands (effective charges and metal-ligand distances) are extracted from the study of the magnetic properties of the first two families of single-ion magnets based on lanthanoid polyoxometalates (POMs), formulated as [Ln(W5O18)2](9-) and [Ln(β2-SiW11O39)2](13-) (Ln = Tb, Dy, Ho, Er, Tm, Yb). This effective CF approach provides a good description of the lowest-lying magnetic levels and the associate…

Sublimable chloroquinolinate lanthanoid single-ion magnets deposited on ferromagnetic electrodes

A new family of chloroquinolinate lanthanoid complexes of the formula A+[Ln(5,7Cl2q)4]−, with Ln = Y3+, Tb3+ and Dy3+ and A+ = Na+, NEt4+ and K0.5(NEt4)0.5+, is studied, both in bulk and as thin films. Several members of the family are found to present single-molecule magnetic behavior in bulk. Interestingly, the sodium salts can be sublimed under high vacuum conditions retaining their molecular structures and magnetic properties. These thermally stable compounds have been deposited on different substrates (Al2O3, Au and NiFe). The magnetic properties of these molecular films show the appearance of cusps in the zero-field cooled curves when they are deposited on permalloy (NiFe). This indic…

Langmuir−Blodgett Films of a Mo-Blue Nanoring [Mo142O429H10(H2O)49(CH3CO2)5(CH3CH2CO2)]30- (Mo142) by the Semiamphiphilic Method

Langmuir monolayers and LB films of the ring-shaped mixed-valence polyoxomolybdate [Mo142O429H10(H2O)49(CH3CO2)5(CH3CH2CO2)]30- (Mo142) dissolved in the aqueous subphase have been successfully fabricated by using the adsorption properties of a DODA monolayer. Infrared and ultraviolet−visible spectroscopy of the LB films indicates that Mo142 and DODA molecules are incorporated within these LB films. X-ray reflectivity experiments indicate that the LB films exhibit a well-defined lamellar structure formed by bilayers of DODA molecules alternating with monolayers of Mo142. Using behenic acid-modified hydrophobic quartz substrate is critical for the formation of the well-defined lamellar struct…

Improving the onset potential and Tafel slope determination of earth-abundant water oxidation electrocatalysts

To date, a plethora of electrocatalysts for the Oxygen Evolution Reaction (OER) have been proposed. For evaluating their electrocatalytic behavior the determination of the onset potential in each studied electrolyte is a key parameter. Nevertheless, this evaluation becomes particularly problematic for first- transition metal catalysts as well as by the use of electroactive collectors ( e.g. Ni foams) whose redox peaks overlap the onset potential. A usual solution to detect the onset potential requires the availabil- ity of in-situ mass spectrometric determination of the generated oxygen. In this work, we present fast and easier available cyclic voltammetry and coulovoltammetric responses to…

2D and 3D bimetallic oxalate-based ferromagnets prepared by insertion of MnIII-salen type complexes

The syntheses, structures and magnetic properties of the compounds of formulae [Mn((R)-salmen)(CH3OH)(CH3CN)][MnCr(ox)3](CH3OH)0.5(CH3CN)1.25 ((R)-1), [Mn((S)-salmen)(CH3OH)(CH3CN)][MnCr(ox)3](CH3OH)0.5(CH3CN)1.25 ((S)-1), [Mn((R)-salmen)(CH3OH)2][MnCr(ox)3](CH2Cl2)0.375(CH3OH)0.125(H2O)0.375 ((R)-2) and [Mn((S)-salmen)(CH3OH)2][MnCr(ox)3](CH2Cl2)0.375(CH3OH)0.375(H2O)0.125 ((S)-2) (ox = oxalate, salmen2− = N,N′-(1-methylethylene)bis(salicylideneiminate)), [Mn(salpn)(CH3OH)1.5(CH3CN)0.5][MnCr(ox)3](CH3OH)0.82(H2O)0.93 (3) (salpn2− = N,N′-(propane)bis(salicylideneiminate)) and [Mn(saltmen)(CH3OH)(CH3CN)][MnCr(ox)3](CH3OH) (4) (saltmen2− = N,N′-(1,1,2,2-tetramethylethylene)bis(salicylideneimi…

Mixed-valence polyoxometalate clusters. III. Vibronic problem for the 2-electron reduced heteropoly blue with the Keggin structure

Abstract A general approach to the vibronic problem of delocalized electronic pairs in mixed-valence compounds is developed and applied to understand the ways of electron delocalization in dodecanuclear polyoxometalate clusters containing two moving electrons. The interplay between electronic and vibronic interactions is examined. The electronic spectrum is shown to consist of two spin triplets 3 T 1 and 3 T 2 and three spin singlets 1 A 1 , 1 E and 1 T 2 levels determined by the double-transfer processes (parameter P ). Jahn-Teller and pseudo-Jahn-Teller problems ( 3 T 1 + 3 T 2 ) ⊗ ( e + t 2 ) and ( 1 A 1 + 1 E + 1 T 2 ) ⊗ ( e + t 2 ) have been considered in the framework of the Piepho-Kr…

Magnetic Langmuir-Blodgett films of ferritin with different iron contents.

Magnetic Langmuir-Blodgett films of four ferritin derivatives with different iron contents containing 4220, 3062, 2200, and 1200 iron atoms, respectively, have been prepared by using the adsorption properties of a 6/1 mixed monolayer of methyl stearate (SME) and dioctadecyldimethylammonium bromide (DODA). The molecular organization of the mixed SME/DODA monolayer is strongly affected by the presence of the water-soluble protein in the subphase as shown by pi-A isotherms, BAM images, and imaging ellipsometry at the water-air interface. BAM images reveal the heterogeneity of this mixed monolayer at the air-water interface. We propose that the ferritin is located under the mixed matrix in thos…

Pressure induced collapse of the charge density wave and Higgs mode visibility in 2H-TaS$_2$

The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides 2H-TaS$_2$ is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density-wave is found to collapse at 8.5~GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5~GPa. Our report constitutes the first observation of such Raman active Higgs mode since the longstand…

Electron delocalization in mixed-valence Keggin polyoxometalates. Ab initio calculation of the local effective transfer integrals and its consequences on the spin coupling.

We present a quantitative evaluation of the influence of the electron transfer on the magnetic properties of mixed-valence polyoxometalates reduced by two electrons. For that purpose, we extract from valence-spectroscopy ab initio calculations on embedded fragments the value of the transfer integrals between W nearest-neighbor atoms in a mixed-valence alphaPW(12)O(40) polyoxowolframate Keggin anion. In contradiction with what is usually assumed, we show that the electron transfer between edge-sharing and corner-sharing WO(6) octahedra have very close values. Considering fragments of various ranges, we analyze the accuracy of calculations on fragments based on only two WO(5) pyramids which s…

Vibronic Model for Intercommunication of Localized Spins via Itinerant Electron

In this article, we propose a vibronic pseudo Jahn–Teller model for partially delocalized mixed-valence molecules aimed to describe the magnetic coupling between the localized spins mediated by the delocalized electron. The simplest partially delocalized system that retains the main studied features is assumed to consist of a one-electron mixed-valence dimer, which is connected to the two terminal magnetic ions. The model involves the following key interactions: electron transfer in the spin-delocalized subsystem of a mixed-valence molecule, which is mimicked by a dimeric unit, coupling of the itinerant electrons with the molecular vibrations, and isotropic magnetic exchange between the loc…

Unravelling the chemical design of spin-crossover nanoparticles based on iron(ii)–triazole coordination polymers: towards a control of the spin transition† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5tc01093d Click here for additional data file.

We present a systematic study of the key synthetic parameters that control the growth of Fe–triazole spin-crossover nanoparticles and the effect of this size modulation on the spin transition.

Three addressable spin qubits in a GdW30 single-ion magnet

Resumen del trabajo presentado a la XXXVI Reunión Bienal de la Real Sociedad Española de Física, celebrada en Santiago de Compostela del 17 al 21 de julio de 2017.

Mixed-valence polyoxometalate clusters. II. Delocalization of electronic pairs in 18-site heteropoly blues with Wells-Dawson structure

Abstract The problem of delocalization of two electrons in the 18-site Wells-Dawson polyoxometalate is examined from a general approach that takes into account both single- and double-transfer processes, as well as the Coulomb interactions between the two delocalized electrons. The electronic energy levels of this mixed-valence cluster are calculated and the conditions giving rise to the stabilization of a singlet ground spin state for the electronic pair are elucidated. It is shown that the spin pairing results from the simultaneous effects of single- and double-electron transfer processes, which are operative even when the two delocalized electrons are fairly widely separated in the Wells…

Modeling the properties of uranium-based single ion magnets

We analyze the magnetic behavior of the five uranium-based SIMs reported in the literature. By combining a corrected crystal field model with the magnetic experimental data, we obtain the lowest-lying magnetic levels and the associated wave functions of the nanomagnets, which are found to be compatible with the observed SMM behavior. Additionally, this approach has allowed us to propose some geometrical considerations and practical advice for experimentalists aiming for the rational design of SIMs and spin qubits based on uranium.

Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2 H − TaS 2

Intercalation of two-dimensional oxalate-bridged molecule-based magnets into layered double hydroxide hosts

Here we report the intercalation of a MnII–CrIII oxalate-bridged extended network into the interlamellar space offered by a ZnII–AlIII LDH host. This material exhibits ferrimagnetic ordering below 3 K from dominant antiferromagnetic interactions between metallic centres through the oxalate linker. Our result opens the door for the design of a completely new sort of hybrid magnetic multilayers from molecule-based magnets and layered inorganic flexible hosts, where the intrinsic properties of both sub-layers can be combined.

Synthesis and properties of dinuclear Ru(II)/Os(II) complexes based on a heteroditopic phenanthroline-terpyridine bridging ligand.

The synthesis and characterization of a series of mono- and dinuclear ruthenium(II) and osmium(II) polypyridyl complexes based on the heteroditopic bridging ligand PT are reported. This ligand incorporates bidentate phen (1,10-phenanthroline) and terdentate tpy (2,2':6',2''-terpyridine) units directly connected by their 3 and 5 positions, respectively. The dinuclear complexes have been synthesized via a Pd(0) catalyzed cross-coupling reaction between a bromo-substituted Ru-phen complex and a tpy derivative incorporating a boronate ester, followed by Ru(II) or Os(II) complexation. The compounds obtained are fully characterized using spectroscopic and electrochemical measurements. The electro…

Magnetic Properties of Mixed-Valence Clusters: Theoretical Approaches and Applications

Vibronic Localization of the Electronic Pair in Polynuclear Mixed-Valence Polyoxometalates*

Fast redox-triggered shuttling motions in a copper rotaxane based on a phenanthroline–terpyridine conjugate

Fast shuttling motions in solution have been observed by cyclic voltammetry in a Cu(I/II)-based [2] rotaxane. In the reported system, the different coordination preferences of both copper oxidation states are exploited to promote the electrochemically-triggered gliding of the ring from a tetra to a pentacoordinated site and vice versa. The thread of this rotaxane consists of a tridentate 2,2':6',2''-terpyridine chelating unit directly bonded through its 5-position to the 3-position of the bidentate 1,10-phenanthroline unit. This distribution reduces to a minimum the distance between the two coordination sites and lessens the congestion around the tetrahedral environment. These two factors h…

Magnetic Excitations in Polyoxometalate Clusters Observed by Inelastic Neutron Scattering:  Evidence for Anisotropic Ferromagnetic Exchange Interactions in the Tetrameric Cobalt(II) Cluster [Co4(H2O)2(PW9O34)2]10-. Comparison with the Magnetic and Specific Heat Properties

The ground-state properties of the tetranuclear Co2+ cluster [Co4(H2O)2(PW9O34)2]10- were investigated by combining specific heat, magnetic susceptibility, and magnetization measurements with a detailed inelastic neutron scattering (INS) study on a fully deuterated sample of K10[Co4(H2O)2(PW9O34)2]·22H2O. As a result of the single ion anisotropy of the octahedral Co2+, the appropriate exchange Hamiltonian of the Co4 spin cluster is anisotropic. INS turns out to be essential for the determination of energy splittings in the ground state resulting from the coupling. Besides the energy pattern, INS provides information about the wave functions of the split ground-state components of the spin c…

Electric field control of the optical properties in magnetic mixed-valence molecules

We propose the use of an electric field stimulus to strongly affect the optical properties of ferromagnetic mixed-valence (MV) dimers. This proposal is based on the prediction of an anomalous Stark effect in the intervalence absorption bands of these multi-electron MV systems. As distinguished from the conventional Stark effect observed in one-electron dimers, a strong change of the intervalence bands accompanies the crossing of the different spin levels caused by the application of an electric field. This new effect can be referred to as giant spin-dependent Stark effect. In spintronics this opens up the possibility for optical detection of the spin state in these magnetic molecules.

Magnetic exchange interaction in clusters of orbitally degenerate ions. II. Application of the irreducible tensor operator technique

Abstract The irreducible tensor operator technique in R3 group is applied to the problem of kinetic exchange between transition metal ions possessing orbitally degenerate ground states in the local octahedral surrounding. Along with the effective exchange Hamiltonian, the related interactions (low-symmetry crystal field terms, Coulomb interaction between unfilled electronic shells, spin–orbit coupling and Zeeman interaction) are also taken into account within a unified computational scheme. Extension of this approach to high-nuclearity systems consisting of transition metal ions in the orbital triplet ground states is also demonstrated. As illustrative examples, the corner-shared D4h dimers…

Synthesis, Structure, and Magnetic Properties of the Oxalate-Based Bimetallic Ferromagnetic Chain {[K(18-crown-6)][Mn(H2O)2Cr(ox)3]}∞ (18-crown-6 = C12H24O6, ox = C2O42-)

The salt [K(18-crown-6)][Mn(H2O)2Cr(ox)3]·0.5(18-crown-6) (1) has been prepared and structurally and magnetically characterized. It crystallizes in the P21/c space group [a = 21.011(2) A, b = 11.265(2) A, c = 15.748(3) A, β = 105.952(6)°, V = 3584(1) A3, and Z = 4] and contains [Mn(H2O)2Cr(ox)3]∞ chains connected through hydrogen bonding to form 2D anionic networks. The magnetic exchange is ferromagnetic [J = +2.23(2) cm-1] in the chain and also in between chains, reaching bulk ferromagnetic ordering below 3.5 K.

Mononuclear lanthanide single molecule magnets based on the polyoxometalates [Ln(W5O18)2]9- and [Ln(beta2-SiW11O39)2]13- (Ln(III) = Tb, Dy, Ho, Er, Tm, and Yb).

The first two families of polyoxometalate-based single-molecule magnets (SMMs) are reported here. Compounds of the general formula [Ln(W(5)O(18))(2)](9-) (Ln(III) = Tb, Dy, Ho, and Er) and [Ln(SiW(11)O(39))(2)](13-) (Ln(III) = Tb, Dy, Ho, Er, Tm, and Yb) have been magnetically characterized with static and dynamic measurements. Slow relaxation of the magnetization, typically associated with SMM-like behavior, was observed for [Ln(W(5)O(18))(2)](9-) (Ln(III) = Ho and Er) and [Ln(SiW(11)O(39))(2)](13-) (Ln(III) = Dy, Ho, Er, and Yb). Among them, only the [Er(W(5)O(18))(2)](9-) derivative exhibited such a behavior above 2 K with an energy barrier for the reversal of the magnetization of 55 K. …

SIMPRE1.2: Considering the hyperfine and quadrupolar couplings and the nuclear spin bath decoherence

SIMPRE is a fortran77code which uses an effective electrostatic model of point charges to predict the magnetic behavior of rare-earth-based mononuclear complexes. In this manuscript, we present SIMPRE1.2, which now takes into account two further phenomena.Firstly, SIMPRE now considers the hyperfine and quadrupolar interactions within the rare-earth ion, resulting in a more complete and realistic set of energy levels and wave functions. Secondly,and in order to widen SIMPRE’s predictive capabilities regarding potential molecular spin qubits, it now includes a routine that calculates an upper-bound estimate of the decoherence time considering only the dipolar coupling between the electron spi…

Hybrid Molecular Magnets Obtained by Insertion of Decamethylmetallocenium Cations into Layered, Bimetallic Oxalate Complexes: [ZIIICp*2][MIIMIII(ox)3] (ZIII=Co, Fe; MIII=Cr, Fe; MII=Mn, Fe, Co, Cu, Zn; ox=oxalate; Cp*=pentamethylcyclopentadienyl)

A new series of hybrid organometallic - inorganic layered magnets with the formula [Z(III)Cp*2][M(II)M(III)(ox)3] (Z(III) = Co, Fe; M(III) = Cr, Fe; M(II) = Mn, Fe, Co, Cu, Zn; ox = oxalate; Cp* = pentamethylcyclopentadienyl) has been prepared. All of these compounds are isostructural and crystallize in the monoclinic space group C2/m, as found by X-ray structure analysis. Their structure consists of an eclipsed stacking of the bimetallic oxalate-based extended layers separated by layers of organometallic cations. These salts show spontaneous magnetization below To, which corresponds to the presence of ferro-, ferri-, or canted antiferromagnetism. Compounds in which the paramagnetic deca-me…

Photoluminescence Enhancement by Band Alignment Engineering in MoS 2 /FePS 3 van der Waals Heterostructures

Single-layer semiconducting transition metal dichalcogenides (2H-TMDs) display robust excitonic photoluminescence emission, which can be improved by controlled changes to the environment and the chemical potential of the material. However, a drastic emission quench has been generally observed when TMDs are stacked in van der Waals heterostructures, which often favor the nonradiative recombination of photocarriers. Herein, we achieve an enhancement of the photoluminescence of single-layer MoS2 on top of van der Waals FePS3. The optimal energy band alignment of this heterostructure preserves light emission of MoS2 against nonradiative interlayer recombination processes and favors the charge t…

Magnetic order in 2D antiferromagnets revealed by spontaneous anisotropic magnetostriction

The temperature dependent order parameter provides important information on the nature of magnetism. Using traditional methods to study this parameter in two-dimensional (2D) magnets remains difficult, however, particularly for insulating antiferromagnetic (AF) compounds. Here, we show that its temperature dependence in AF MPS$_{3}$ (M(II) = Fe, Co, Ni) can be probed via the anisotropy in the resonance frequency of rectangular membranes, mediated by a combination of anisotropic magnetostriction and spontaneous staggered magnetization. Density functional calculations followed by a derived orbital-resolved magnetic exchange analysis confirm and unravel the microscopic origin of this magnetiza…

2D Bimetallic Oxalate‐Based Ferromagnets with Inserted [Fe(4‐Br‐sal 2 ‐trien)] + and [Fe(3‐R‐sal 2 ‐trien)] + (R = Br, Cl and CH 3 O) Fe III Spin‐Crossover Complexes

The syntheses, structures and magnetic properties of the compounds of formula [FeIII(4-Br-sal2-trien)][MnIICrIII(ox)3]0.67Cl0.33·CH3OH_solvate (1), [FeIII(3-Br-sal2-trien)][MnIICrIII(ox)3]·(CH3CN)2 (2), [FeIII(3-Cl-sal2-trien)][MnIICrIII(ox)3]·(CH3OH)2·(CH3CN)2 (3) and [FeIII(3-CH3O-sal2-trien)][MnIICrIII(ox)3]·(CH3OH)·(H2O)1.5·(CH2Cl2)0.5 (4) are reported. The four structures present a 2D honeycomb anionic layer formed by MnII and CrIII ions linked through oxalate ligands and a cationic layer of the FeIII complexes intercalated between the 2D oxalate network. The main differences compared with previous 2D oxalate-based structures are the presence of double layers of cations in compounds 1,…

Design of Bistable Gold@Spin‐Crossover Core–Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching

&lt;p&gt;A simple protocol to prepare core-shell gold@spin-crossover (Au@SCO) nanoparticles (NPs) based on the 1D spin-crossover [Fe(Htrz)&lt;sub&gt;2&lt;/sub&gt;(trz)](BF&lt;sub&gt;4&lt;/sub&gt;) coordination polymer is reported. The synthesis relies on a two-step approach consisting on a partial surface ligand substitution of the citrate-stabilized Au NPs followed by the controlled growth of a very thin layer of the SCO polymer. As a result, colloidally stable core@shell spherical NPs of 19 nm in size exhibiting a narrow distribution in sizes have been obtained, revealing a switchable SCOshell of &lt;i&gt;ca.&lt;/i&gt;4 nm. Temperature-dependent charge transport measurements of an electri…

Intramolecular proton transfer boosts water oxidation catalyzed by a Ru complex

We introduce a new family of complexes with the general formula [Run(tda)(py)2]m+ (n = 2, m = 0, 1; n = 3, m = 1, 2+; n = 4, m = 2, 32+), with tda2&ndash; being [2,2&prime;:6&prime;,2&Prime;-terpyridine]-6,6&Prime;-dicarboxylate, including complex [RuIV(OH)(tda-&kappa;-N3O)(py)2]+, 4H+, which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 32+ under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV&ndash;vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), …

1D antiferromagnetism in spin‐alternating bimetallic chains

The magnetic and thermal properties of the ordered bimetallic chain CoNi(EDTA)⋅6H2O in the very low‐temperature range are reported. The magnetic behavior does not exhibit the characteristic features of 1D ferrimagnets, but a continuous decrease of χmT towards zero at absolute zero. This 1D antiferromagnetic behavior results from an accidental compensation between the moments located at the two sublattices. This behavior, as well as the specific‐heat results, are modeled on the basis of an Ising‐exchange model that considers both alternating spins and Landé factors, and a zero‐field splitting on the Ni site. Eugenio.Coronado@uv.es ; Fernando.Sapina@uv.es

Influence of morphology in the magnetic properties of layered double hydroxides

We report the controlled synthesis of magnetic CoAl and NiFe layered double hydroxides (LDHs) endowed with well-defined morphology (hexagonal and flower-like shapes) by means of modified homogeneous precipitation. These layered magnets display high crystallinity and micrometric size, thus offering a perfect scenario for the elucidation of the role exerted by distortion of the layers in their magnetic behaviour. The magnetic properties have been investigated by means of DC and AC magnetic susceptibility measurements and isothermal magnetization, demonstrating that the distortion of the nanosheets induces a magnetically more disordered behaviour, with marked spin-glass nature, independently o…

High nuclearity magnetic clusters: Magnetic properties of a nine cobalt cluster encapsulated in a polyoxometalate, [Co9(OH)3(H2O)6(HPO4)2(PW9O34)3]16⊕

Gd-based single-ion magnets with tunable magnetic anisotropy: Molecular design of spin qubits

et al.

A chemical and electrochemical multivalent memory made from FeNi3-graphene nanocomposites

FeNi3-graphene nanocomposites present in acetonitrile solutions a redox couple with an electrochemical hysteresis of 2.4 V between the oxidation and the reduction maxima. In view of the high energy required for the reverse transitions, they are here proposed as chemical multilevel memories: permanent, after drying, or erasable in electrolytes, respectively. Keywords: FeNi3-graphene nanocomposites, Voltammetry, Coulovoltammetry, Redox couple, Redox hysteresis

A novel paramagnetic molecular superconductor formed by bis(ethylenedithio)tetrathiafulvalene, tris(oxalato)ferrate(iii) anions and bromobenzene as guest molecule: ET4[(H3O)Fe(C2O4)3]·C6H5Br

The new paramagnetic molecular superconductor ET4[(H3O)Fe(C2O4)3]·C6H5Br (1) (Tc = 4.0 K) contains layers of superconducting ET donors alternating with paramagnetic hexagonal layers formed by (H3O)+, [Fe(C2O4)3]3− and guest C6H5Br molecules located in the hexagonal cavities. Conductivity measurements show metallic behavior from room temperature with a minimum in the resistivity at ca. 50 K followed by a smooth increase and a sharp drop in the resistivity with an onset at 4.0 K and a zero resistance at ca. 1.0 K. Magnetoresistance measurements indicate that Hc1 is about 7 mT and that Hc2 is very anisotropic (Hc2⊥ ≥ 5.5 T and Hc2|| ≈ 0.5 T). Magnetic susceptibility measurements show the expec…

Metal Phosphonates Based on {[(Benzimidazol‐2‐ylmethyl)imino]bis(methylene)}bis(phosphonic Acid): Syntheses, Structures and Magnetic Properties of the Chain Compounds [M{(C 7 H 5 N 2 )CH 2 N(CH 2 PO 3 H) 2 }](M = Mn, Fe, Co, Cu, Cd)

Five compounds based on {[(benzimidazol-2-ylmethyl)imino]bis(methylene)}bis(phosphonic acid) [(C7H5N2)CH2N(CH2PO3H2)2], namely [M{(C7H5N2)CH2N(CH2PO3H)2}] [M = Mn (1), Fe (2), Co (3), Cu (4), Cd (5)] have been synthesized under hydrothermal conditions. These compounds are isostructural, crystallizing in the orthorhombic space group Pbca, with a = 15.331(2), b = 10.7150(16), and c = 16.715(2) A for 1; a = 15.320(3), b = 10.477(2), and c = 16.764(3) A for 2; a = 15.207(2), b = 10.4626(16), and c = 16.794(3) A for 3; a = 15.101(3), b = 10.3517(17), and c = 16.997(3) A for 4; and a = 15.4679(19), b = 10.8923(13), and c = 16.6175(19) for 5. Each compound shows a one-dimensional chain structure w…

Magneto-Structural Correlations in μ-Halo Bridged Copper(II) Chains

To design synthetic pathways to systems of desired properties is a growing challenge for inorganic chemist. Our current interest in this area is focused on copper(II) chemistry. Besides to advance in the understanding of the factors determining the conformation around copper(II) in the solid state, we intend to gain insight into the chemical and structural effects that govern exchange coupling interactions in condensed species. In this context, we have approached the synthesis and characterization of a wide set of pentacoordinated Cu(LIII)XY complexes (LIII=tridentate ligand, X=coordinating anion, Y=coordinating or non-coordinating anion) showing a great structural diversity (including mono…

Hexagonal nanosheets from the exfoliation of Ni2+-Fe3+ LDHs: a route towards layered multifunctional materials

Here we report the synthesis of a crystalline micrometric-sized hexagonal-shaped Ni2+-Fe3+ LDH by following a modified homogeneous precipitation method. The exfoliation of the material in formamide leads to stable suspensions of hexagonal nanometric sheets, which have been extensively characterized. Our data confirm that the intrinsic properties of the bulk material are retained by these segregated nanosheets, thus opening the door for their use in the development of layered multifunctional materials.

Optical mercury sensing using a benzothiazolium hemicyanine dye.

[structure: see text] The selectivity and sensitivity of a benzothiazolium hemicyanine dye toward mercury(II) in aqueous solutions are described. Mercury ions coordinate to the dye forming a 1:1 complex. This interaction induces a color change in the dye at micromolar concentrations of mercury. Furthermore, the color change and quenching of the dye emission are selective for mercury when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II).

A novel polynitrile ligand with different coordination modes: Synthesis, structure and magnetic properties of the series [M(tcnoprOH)2(H2O)2] (M=Mn, Co and Cu) (tcnoprOH−=[(NC)2CC(OCH2CH2CH2OH)C(CN)2]−)

International audience; A novel polynitrile ligand (tcnoprOH− = [(NC)2CC(OCH2CH2CH2OH)C(CN)2]−) with up to five potentially coordinating groups has been synthesized in a one-pot reaction from a cyclic acetal and malononitrile. The combination of this novel ligand with different transition metal ions has led to the synthesis of two different structural types with the same formula but with different coordination modes in the ligand. Mn(II) and Cu(II) lead to a μ2-N,O-coordinating mode in the series of compounds formulated as [M(N,O-tcnoprOH)2(H2O)2] (M = MnII (1) and CuII (2)), whereas Co(II) and, most probably Ni(II), lead to a μ2-N,N′-coordinating mode in [Co(N,N′-tcnoprOH)2(H2O)2] (3). Bot…

Insertion of single-ion magnets based on mononuclear Co(II) complexes into ferromagnetic oxalate-based networks

The 1 : 2 and 1 : 1 Co(ii) complexes of the L ligand (L = 6-(3,5-diamino-2,4,6-triazinyl)2,2'-bipyridine) with formulas [CoII(L)2](ClO4)2·0.5MeCN·Et2O (1) and [CoII(L)(CH3CN)2(H2O)](ClO4)2·MeCN (2) have been prepared. The structural and magnetic characterization of the two compounds shows that they contain octahedral high-spin Co(ii) and present a field-induced slow relaxation of the magnetization. 1 has been inserted into a bimetallic oxalate-based network leading to a novel achiral 3D compound of formula [CoII(L)2][MnIICrIII(ox)3]2·(solvate) (3) exhibiting ferromagnetic ordering below 4.6 K. EPR measurements suggest a weak magnetic coupling between the two sublattices.

Synthesis, Crystal Structure, and Properties of Multicomponent Bis(ethylenedithio)tetrathiafulvalene Charge-Transfer Salts of the [Mo3S7Br6]2- Cluster

A new family of bis(ethylenedithio)tetrathiafulvalene (ET) radical salts has been prepared in the presence of a triangular molybdenum sulfide cluster of formula [Mo 3 S 7 Br 6 ] 2 - , which contains highly electrophilic axialsulfur atoms. A systematic change in the experimental conditions yields five different salts, namely (ETA)2(ET B )[Mo 3 S 7 Br 6 ] 2 . CH 2 Br 2 (1), (ETA)(ET B )Mo 3 S 7 Br 6 ].1.1CH 2 Br 2 (2), (ETA)(ETB)(ET C ){[Mo 3 S 7 Br 6 ]Br}.0.5C 2 H 4 Cl 2 (3), (ET)((n-Bu 4 )N)-[Mo 3 S 7 Br 6 ] (4), and (ET)(Ph4P)[Mo 3 S 7 Br 6 ].0.5CH 3 CN (5), where the ET subscript denotes crystallographically independent molecules. The five compounds have been structurally characterized, a…

Hybrid molecular conductors

One of the most important trends in the field of organic conductors aims towards the design of hybrid materials, following the strategy of combining in a single compound organic cationic radicals able to give rise to conducting architectures with functional molecular anions able to add a second physical property of interest. Ferromagnetic metals, magnetic superconductors, chiral conductors and switchable conductors are some of the most recent and spectacular materials obtained from this approach. The design and physical studies of some relevant examples are discussed and highlighted.

Magnetic ordering in an (Fe0.2Cr0.8)1.5[Cr(CN)6] Prussian blue analogue studied with synchrotron radiation based spectroscopies

The appearance of magnetic order in the (Fe0.2Cr0.8)1.5[Cr(CN)6]·15H2O Prussian blue analogue at low temperature has been investigated by means of synchrotron radiation-based X-ray absorption spectroscopy and X-ray magnetic circular dichroism. With the help of ligand field multiplet analysis we have been able to identify the oxidation states of the metallic cations present in the sample and their evolution with temperature. Our experiments reveal that the appearance of ferromagnetic order is triggered by the transformation of CrIII cations to CrII high-spin caused by a transfer of electrons from the Fe to the Cr resulting in an increase of the magnetic interactions within the (Cr, Cr) subla…

Synthesis, Structure, and Magnetic Properties of [(S)-[PhCH(CH3)N(CH3)3]][Mn(CH3CN)2/3Cr(ox)3]·(CH3CN)_(solvate), a 2D Chiral Magnet Containing a Quaternary Ammonium Chiral Cation

The synthesis, structure, and magnetic properties of a novel oxalate-based bimetallic magnet obtained by using the chiral (S)-trimethyl-(1-phenyl-ethyl)-ammonium, ((S)-[PhCH(CH3)N(CH3)3](+)), cation as template is reported. This compound can be formulated as [(S)-[PhCH(CH3)N(CH3)3]][Mn(CH3CN)2/3Cr(ox)3] x (CH3CN)_(solvate), and it crystallizes in the chiral trigonal space group P3. It shows a distorted two-dimensional honeycomb structure formed by Mn(II) and Cr(III) ions connected through oxalate anions with [(S)-[PhCH(CH3)N(CH3)3](+) cations and solvent molecules intercalated between the oxalate layers. Two-thirds of the Mn(II) ions of the honeycomb anionic network are heptacoordinated. Th…

Size-Dependent Spin Switching in Robust Fe-triazole@SiO2 Spin-Crossover Nanoparticles with Ultrathin Shell

&lt;p&gt;A familly of chemically robust hybrid [Fe(Htrz)2(trz)](BF4)@SiO2nanoparticles (NPs) presenting different sizes (from ca. 90 to 28 nm) and an ultrathin silica shell (&lt; 3 nm) have been prepared. All NPs present a characteristic abrupt spin transition with a subsequent decrease in the width of the thermal hysteresis upon reducing the NP size.&lt;br&gt;&lt;/p&gt;

Electronic and vibronic problems of nanosized mixed valence clusters: Advances and challenges

Here we discuss the electronic and vibronic problems of mixed valency (MV) in molecular clusters which are of current interest in areas as diverse as solid-state chemistry, biochemistry, and molecular magnetism. Modern research in these areas is focused on the nanosized clusters at the border between classical and quantum scales and for this reason they are particularly difficult to study. First, we describe a general approach to the evaluation of the energy pattern of MV systems containing arbitrary number of localized spins and itinerant electrons with due account for the double exchange and other relevant interactions, like interelectronic Coulomb repulsion in instantly localized configu…

Self-Assembly of a Copper(II)-Based Metallosupramolecular Hexagon

The self-assembly of a 1:1 mixture of copper(II) ions and a rigid heteroditopic ligand L containing phen and terpy binding units gives rise in the solid state to green crystals of a hexanuclear metallamacrocycle 1. X-ray crystallography reveals that 1 consists of molecular hexagons of the grid-type family in which each metal ion is bound to two different ligands through the phen and terpy units, plus a weakly coordinated PF6 (-) anion in a highly distorted octahedral geometry. ES-MS studies of acetonitrile solutions of L and copper(II) in a 1:1 ratio show mixtures of polynuclear complexes in which trinuclear L3Cu3 species are predominant.

Alkoxide-intercalated CoFe-layered double hydroxides as precursors of colloidal nanosheet suspensions: structural, magnetic and electrochemical properties

Alkoxide-intercalated CoFe-layered double hydroxides (CoFe–LDHs) were synthesized via the non-aqueous methanolic route. According to powder X-ray diffraction and field emission scanning electron microscopy, they exhibit a nanosized plate-like morphology with a basal space of 9.21 A. The hydrolysis of the material in water leads to colloidal suspensions of nanosheets with lateral dimensions of about 20 nm and thicknesses of ca. 4 nm as demonstrated by atomic force microscopy and dynamic light scattering. Atomic resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy confirm the high crystalline quality of the crystals and the proper Co/Fe stoichio…

Magnetic exchange interactions in the heteropoly complexes [M4(H2O)2(PW9O34)2]10− [M=Co(II) and Cu(II)]

The magnetic properties of the heteropolyanions [M4(H2O)2(PW9O34)2]10− [M=Co(II) and Cu(II)] down to 4 K are reported. Their individual heteropoly molecules contain a rhomblike arrangement formed by four coplanar MO6 octahedra sharing edges. The magnetic properties support an intramolecular ferromagnetic exchange in the Co(II) tetramer, and antiferromagnetic exchange in the Cu(II) tetramer. These behaviors are discussed assuming anisotropic exchange in the Co(II) compound, and Heisenberg exchange in the Cu(II) compound. Carlos.Gomez@uv.es

[MnM(egta)]. 8H2 = (M = Mn, Cd): Verbindungen mit einem neuartigen zweidimensionalen magnetischen Gitter

A symmetry adapted approach to the dynamic Jahn-Teller problem: Application to mixed-valence polyoxometalate clusters with keggin structure

In this article, we present a symmetry-adapted approach aimed to the accurate solution of the dynamic vibronic problem in large scale Jahn-Teller (JT) systems. The algorithm for the solution of the eigen-problem takes full advantage of the point symmetry arguments. The system under consideration is supposed to consist of a set of electronic levels mixed by the active JT and pseudo JT vibrational modes. Applying the successive coupling of the bosonic creation operators, we introduce the irreducible tensors that are called multivibronic operators. Action of the irreducible multivibronic operators on the vacuum state creates the vibrational symmetry adapted basis that is subjected to the Gram-…

Effect of conductivity of hole injection layer on the performance of a blue light emitting solution processable OLED

The performance of blue emitting OLED devices, using a polyspiro as blue light emitting polymer, were studied as a function of the conductivity of a novel hybrid hole injection material. The hole injection material is based on a polyarylamine using a molecular magnet as oxidant. The charge density and the luminance of the devices changed considerably with increasing conductivity of the hole injection layer. The change in device performance can be attributed to a change from a hole limited device to a balanced charge carrier device and eventually to an electron limited device. The performance of the optimized device configuration is significantly improved with respect to a device making use …

Magnetic properties of hybrid molecular materials based on oxalato complexes

Abstract The use of [MIII(ox)3]3− (MIII=Ru, Rh) complexes as building blocks for hybrid molecular materials is highlighted with two different synthetic approaches. The first strategy is the combination of organic donors and [RuIII(ox)3]3− units, resulting in the radical salt of formula TTF3[Ru(ox)3]·0.5EtOH·4H2O (1) which shows coexistence of paramagnetism and semiconducting properties. The second approach is the synthesis of extended 2D bimetallic oxalato-bridged networks of general formula [FeCp2 *][MIIRh(ox)3] in which paramagnetic layers of decamethylferricinium cations are alternated with paramagnetic bimetallic layers.

LOCAL STRUCTURE OF THE CuCu (EDTA) (H2O)2, 2H2O AMORPHOUS COMPLEX : A JOINT MAGNETIC, LAXS, AND MOLECULAR MECHANICS INVESTIGATION

The short range order in the amorphous CuCu (EDTA) (H2O)2, 2H2O is studied by Large Angle X-ray Scattering (LAXS) and molecular mechanics. Three conformations of the complex molecule are shown to be energetically equivalent, two of which are simultaneously present in the amorphous material.

Coherent coupling between vortex bound states and magnetic impurities in 2D layered superconductors

Bound states in superconductors are expected to exhibit a spatially resolved electron-hole asymmetry which is the hallmark of their quantum nature. This asymmetry manifests as oscillations at the Fermi wavelength, which is usually tiny and thus washed out by thermal broadening or by scattering at defects. Here we demonstrate theoretically and confirm experimentally that, when coupled to magnetic impurities, bound states in a vortex core exhibit an emergent axial electron-hole asymmetry on a much longer scale, set by the coherence length. We study vortices in 2H-NbSe2 and in 2H-NbSe1.8S0.2 with magnetic impurities, characterizing these with detailed Hubbard-corrected density functional calcu…

Molecular Magnetic Materials from Polyoxometalates

The significance of polyoxometalates in the field of molecular magnetism is discussed. We show that this kind of inorganic complexes provides remarkable examples for the study of the exchange interactions in clusters. On the other hand, we examine the possibility of using these metal oxide anions as magnetic components of molecular materials containing organic tetrathiafulvalenes as electron donor molecules.

ChemInform Abstract: Multifunctionality in Hybrid Magnetic Materials Based on Bimetallic Oxalate Complexes

This tutorial review illustrates the design of multifunctional oxalate-based magnetic materials through the combination of the intrinsic magnetism of the metal–organic framework and the additional properties introduced by several organic/inorganic functional cations.

Mixed-valence polyoxometalate clusters. I. Delocalization of electronic pairs in dodecanuclear heteropoly blues with keggin structure

Abstract The problem of delocalization of a pair of electrons over dodecanuclear polyoxometalate clusters with the Keggin structure is considered with the aim of explaining the spin pairing in these multi-nuclear mixed-valence systems. A general approach that considers the Coulomb interactions between the two delocalized electrons, as well as the single and double electron transfer processes which can be operative in delocalization of the electronic pairs is developed. The new approach is based on the site-symmetry concept which makes possible a group theoretical classification for the delocalized states of electronic pairs. This procedure proves to be very efficient in the calculation of t…

A family of layered chiral porous magnets exhibiting tunable ordering temperatures.

A simple change of the substituents in the bridging ligand allows tuning of the ordering temperatures, Tc, in the new family of layered chiral magnets A[M(II)M(III)(X2An)3]·G (A = [(H3O)(phz)3](+) (phz = phenazine) or NBu4(+); X2An(2-) = C6O4X2(2-) = 2,5-dihydroxy-1,4-benzoquinone derivative dianion, with M(III) = Cr, Fe; M(II) = Mn, Fe, Co, etc.; X = Cl, Br, I, H; G = water or acetone). Depending on the nature of X, an increase in Tc from ca. 5.5 to 6.3, 8.2, and 11.0 K (for X = Cl, Br, I, and H, respectively) is observed in the MnCr derivative. Furthermore, the presence of the chiral cation [(H3O)(phz)3](+), formed by the association of a hydronium ion with three phenazine molecules, lead…

Does the thermal evolution of molecular structures critically affect the magnetic anisotropy?

A dysprosium based single-ion magnet is synthesized and characterized by the angular dependence of the single-crystal magnetic susceptibility. Ab initio and effective electrostatic analyses are performed using the molecular structures determined from single crystal X-ray diffraction at 20 K, 100 K and 300 K. Contrary to the common assumption, the results reveal that the structural thermal effects that may affect the energy level scheme and magnetic anisotropy below 100 K are negligible.

Tuning size and thermal hysteresis in bistable spin crossover nanoparticles.

Nanoparticles of iron(II) triazole salts have been prepared from water-organic microemulsions. The mean size of the nanoparticles can be tuned down to 6 nm in diameter, with a narrow size distribution. A sharp spin transition from the low spin (LS) to the high spin (HS) state is observed above room temperature, with a 30-40-K-wide thermal hysteresis. The same preparation can yield second generation nanoparticles containing molecular alloys by mixing triazole with triazole derivatives, or from metallic mixtures of iron(II) and zinc(II). In these nanoparticles of 10-15 nm, the spin transition "moves" towards lower temperatures, reaching a 316 K limit for the cooling down transition and mainta…

Near Room-Temperature Memory Devices Based on Hybrid Spin-Crossover@SiO2Nanoparticles Coupled to Single-Layer Graphene Nanoelectrodes

The charge transport properties of SCO [Fe(Htrz)2 (trz)](BF4 ) NPs covered with a silica shell placed in between single-layer graphene electrodes are reported. A reproducible thermal hysteresis loop in the conductance above room-temperature is evidenced. This bistability combined with the versatility of graphene represents a promising scenario for a variety of technological applications but also for future sophisticated fundamental studies.

Core–Shell Nanoparticles: Design of Bistable Gold@Spin‐Crossover Core–Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching (Adv. Mater. 27/2019)

Apoferritin-encapsulated Ni and Co superparamagnetic nanoparticles

Ni and Co nanoparticles (average diameters 3 and 3.5 nm) have been prepared within the apoferritin cavity. The protein shell prevents bulk aggregation of the metal particles, rendering them water soluble. X-Ray diffraction, transmission electronic microscopy and magnetization measurements have been used for characterizing the nanoparticles. The magnetic study of both nanoparticles confirmed the expected superparamagnetic behavior.

Incorporation of Pd nanoparticles in mesostructured silica

Monodisperse Pd nanoparticles were prepared by controlled reduction in organic phase and subsequent transfer to aqueous phase. A systematic study was carried out to finely tune nanoparticle size and optimize particle size distribution. The use of 4-dimethylaminopyridine as a transfer agent allowed for the easy and quantitative extraction of the Pd to the aqueous phase. The quaternary amine-functionalized metal nanoparticles were then used as metallic micelle replicas to grow silica around them. This novel and facile metal incorporation method provided an excellent dispersion and homogeneity of Pd nanoparticles on silica supports. In addition, cationic surfactants, such as cetyltrimethylammo…

Defective dicubane-like tetranuclear nickel(II) cyanate and azide nanoscale magnets.

Four tetrameric nickel(II) pseudohalide complexes have been synthesized and structurally, spectroscopically, and magnetically characterized. Compounds 1-3 are isostructural and exhibit the general formula [Ni(2)(dpk·OH)(dpk·CH(3)O)(L)(H(2)O)](2)A(2)·2H(2)O, where dpk = di-2-pyridylketone; L = N(3)(-), and A = ClO(4)(-) for 1, L = NCO(-) and A = ClO(4)(-) for 2, and L = NCO(-) and A = NO(3)(-) for 3. The formula for 4 is [Ni(4)(dpk·OH)(3) (dpk·CH(3)O)(2)(NCO)](BF(4))(2)·3H(2)O. The ligands dpk·OH(-) and dpk·CH(3)O(-) result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. The four tetramers exhibit a dicubane-like core with two missing vertexes where the…

Role of Deprotonation and Cu Adatom Migration in Determining the Reaction Pathways of Oxalic Acid Adsorption on Cu(111)

Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and first principles theoretical calculations have been used to gain insight into the fundamental processes involved in the adsorption and self-assembly of oxalic acid on Cu(111). The experimental data demonstrate that several reaction pathways are involved in the chemisorption of oxalic acid on Cu(111), one of which leads to deprotonation of the acid into oxalate molecules that form ordered structures on the surface. Theoretical calculations indicate that the adsorption of oxalate molecules is not stable on the surface unless copper adatoms are taken into consideration. Coordination with copper adatoms prevents ox…

Self-assembled monolayers on a ferromagnetic permalloy surface.

Self-assembled monolayers (SAMs) are nowadays broadly used as surface protectors or modifiers and play a key role in many technological applications. This has motivated the study of their formation in all kind of materials; however, and despite the current interest in molecular spintronics, the study of SAMs on ferromagnetic surfaces remains almost unexplored. In this paper, we report for the first time a methodology for the formation of SAMs of n-alkylphosphonic acids on permalloy in ambient conditions. The formed monolayers have been fully characterized by means of contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, matrix assisted laser desorption ioniz…

Cover Feature: Boosting the Supercapacitive Behavior of CoAl Layered Double Hydroxides via Tuning the Metal Composition and Interlayer Space (Batteries & Supercaps 6/2020)

Magnetic exchange between metal ions with unquenched orbital angular momenta: basic concepts and relevance to molecular magnetism

This review article is a first attempt to give a systematic and comprehensive description (in the framework of the unified theoretical approach) of the exchange interactions in polynuclear systems based on orbitally degenerate metal ions in the context of their relevance to the modern molecular magnetism. Interest in these systems is related to the fundamental problems of magnetism and at the same time steered by a number of impressive potential applications of molecular magnets, like high-density memory storage units, nanoscale qubits, spintronics and photoswitchable devices. In the presence of orbital degeneracy, the conventional spin Hamiltonian (Heisenberg–Dirac–van Vleck model) becomes…

Increasing the Ordering Temperatures in Oxalate-Based 3D Chiral Magnets:  the Series [Ir(ppy)2(bpy)][MIIMIII(ox)3]·0.5H2O (MIIMIII = MnCr, FeCr, CoCr, NiCr, ZnCr, MnFe, FeFe); bpy = 2,2‘-Bipyridine; ppy = 2-Phenylpyridine; ox = Oxalate Dianion)

The synthesis, structure, and physical properties of a novel series of oxalate-based bimetallic magnets obtained by using the Ir(ppy)2(bpy)]+ cation as a template of the bimetallic [MIIMIII(ox)3]- ...

Controllable coverage of chemically modified graphene sheets with gold nanoparticles by thermal treatment of graphite oxide with N,N-dimethylformamide

Abstract We describe a simple chemical method to reduce and functionalize graphite oxide by reaction with dimethylformamide under controlled heating. Our experiments suggest that the reaction conditions assist the decomposition of the solvent to produce dimethylamine molecules that can react with the oxygen-rich functional groups covering the surface of the exfoliated layers of graphene, therefore generating chemically modified graphene (CMG). These N-functionalities have been next used as anchoring points for the grafting of Au nanoparticles. Given that the functionalization extent can be controlled with the temperature and reaction time, our approach can be considered as a straightforward…

Quantum Cellular Automata: a Short Overview of Molecular Problem

International audience

Breathing effect in a cobalt phosphonate upon dehydration/rehydration: a single-crystal-to-single-crystal study.

Two cobalt phosphonates, [Co2(2,2′-bpy)2(H2O)(pbtcH)] (1) and [Co2(H2O)(pbtcH)(phen)2] (2; pbtcH5=5-phosphonatophenyl-1,2,4-tricarboxylic acid, 2,2′-bpy=2,2′-bipyridine, phen=1,10-phenanthroline), with layer structures are reported. Compound 1 contains O-C-O and O-P-O bridged tetramers of Co4, which are further connected by pbtcH(4-) units to form a layer. In compound 2, the cobalt tetramers made up of water-bridged Co2 dimers and O-P-O linkages are connected into a layer by pbtcH(4-) units. Upon dehydration, compounds 1 and 2 experience single-crystal-to-single-crystal (SC-SC) structural transformations to form [Co2(2,2′-bpy)2(pbtcH)] (1 a) and [Co2(pbtcH)(phen)2] (2 a), respectively. The …

Structural, thermal and photomagnetic properties of spin crossover [Fe(bpp)2]2+ salts bearing [Cr(L)(ox)2]- anions

International audience; This paper is divided into two parts: in the first part, the influence of solvate molecules on the magnetic properties of spin crossover salts of [Fe(bpp)(2)][Cr(L)(ox)(2)]ClO(4) x nS (bpp = 2,6-bis(pyrazol-3yl)pyridine; L = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen); ox = oxalate dianion; S = solvent) is analyzed. The second part is devoted to the photomagnetic properties of the previously reported [Fe(bpp)(2)][Cr(L)(ox)(2)](2) family of compounds. The study describes the crystal structure, differential scanning calorimetry (DSC) and magnetic properties of [Fe(bpp)(2)][Cr(bpy)(ox)(2)]ClO(4) x EtOH x 4 H(2)O (1) and [Fe(bpp)(2)][Cr(phen)(ox)(2)]ClO(4) x 1.5 …

Conductive Hybrid Films of Polyarylamine Electrochemically Oxidized with the Molecular Nanomagnet [Mn12O12(H2O)4-(C6F5COO)16]

Optimal coupling of HoW$_{10}$ molecular magnets to superconducting circuits near spin clock transitions

A central goal in quantum technologies is to maximize $G$T$_{2}$, where $G$ stands for the coupling of a qubit to control and readout signals and T$_{2}$ is the qubit's coherence time. This is challenging, as increasing $G$ (e.g. by coupling the qubit more strongly to external stimuli) often leads to deleterious effects on T$_{2}$. Here, we study the coupling of pure and magnetically diluted crystals of HoW$_{10}$ magnetic clusters to microwave superconducting coplanar waveguides. Absorption lines give a broadband picture of the magnetic energy level scheme and, in particular, confirm the existence of level anticrossings at equidistant magnetic fields determined by the combination of crysta…

Magnetic polyoxometalates: from molecular magnetism to molecular spintronics and quantum computing.

In this review we discuss the relevance of polyoxometalate (POM) chemistry to provide model objects in molecular magnetism. We present several potential applications in nanomagnetism, in particular, in molecular spintronics and quantum computing.

Structural, Thermal, and Magnetic Study of Solvation Processes in Spin-Crossover [Fe(bpp)2][Cr(L)(ox)2]2·nH2O Complexes

The influence of lattice water in the magnetic properties of spin-crossover [Fe(bpp)2]X2.nH2O salts [bpp = 2,6-bis(pyrazol-3-yl)pyridine] is well-documented. In most cases, it stabilizes the low-spin state compared to the anhydrous compound. In other cases, it is rather the contrary. Unraveling this mystery implies the study of the microscopic changes that accompany the loss of water. This might be difficult from an experimental point of view. Our strategy is to focus on some salts that undergo a nonreversible dehydration-hydration process without loss of crystallinity. By comparison of the structural and magnetic properties of original and rehydrated samples, several rules concerning the r…

Recent advances in polyoxometalate-containing molecular conductors

The recent advances in crystalline conducting molecular materials based on polyoxometalates (POMs) and organic donors of the tetrathiafulvalene (TTF) family or perylene are discussed. We emphasise the wide diversity of POM structural types and the variety of packing architectures for the organic molecules that can be induced by these inorganic anions. Besides structural effects, we show that these hybrids can have interesting electric and/or magnetic properties. Thus, in the last years the common belief that this type of radical salts containing such big and highly charged anions could only exhibit poor conducting properties has been refuted by the production of new materials exhibiting hig…

Polyoxometalate salts of cationic nitronyl nitroxide free radicals

The cationic nitronyl nitroxide free radical of the N-methylpyridinium type p-MepyNN + has been combined with [Mo 8 0 26 ] 4- and Keggin [SiW 12 0 40 ] 4- polyanions to afford salts ( p-MepyNN) 4 [Mo 8 0 26 ] DMSO (DMSO = dimethylsulfoxide) (1) and (p-MepyNN)4[SiW 12 0 40 ] 6DMF (DMF = dimethylformamide) (2). Herein, their structural and magnetic properties are described.

Polymer solar cells based on diphenylmethanofullerenes with reduced sidechain length

Diphenylmethanofullerenes (DPMs) show interesting properties as acceptors in polymer bulk heterojunction solar cells due to the high open circuit voltages they generate compared to their energy levels. Here we investigate the effect of reducing the alkane sidechain length of the DPMs from C12 to C6 in the properties of the solar cell. This change leads to an increase in the electron mobility, thus allowing for a lower fullerene content, which in turn results in an increase in the short circuit current and, finally, in an increase in the efficiency of the device (from 2.3 to 2.6%) due to the higher concentration of the more absorbing polymer in the film. Atomic force microscopy images and ex…

Coherent Manipulation of Polarization in Mixed-Valence Compounds by Electric Pulse via Landau–Zener Transitions

In this contribution, we predict and theoretically investigate the effects of the electric field pulse in mixed valence (MV) dimers. These systems exhibit bistability with a large internal dipole moment mediated by the itinerant electron trapped by the vibronic coupling. In this sense, they are similar to single molecular magnets (SMMs) that are bistable systems possessing large long-living magnetization and exhibiting Landau−Zener (LZ) transitions. We propose a scheme for a controllable LZ tunnelling in MV systems that provides also a possibility to control the dipole moment of a dimeric MV unit. It is supposed that the static electric field initially polarizes the system, and then the uni…

Hexakis-adducts of [60]fullerene as molecular scaffolds of polynuclear spin-crossover molecules

A family of hexakis-substituted [60]fullerene adducts endowed with the well-known tridentate 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand for spin-crossover (SCO) systems has been designed and synthesized. It has been experimentally and theoretically demonstrated that these molecular scaffolds are able to form polynuclear SCO complexes in solution. UV-vis and fluorescence spectroscopy studies have allowed monitoring of the formation of up to six Fe(ii)–bpp SCO complexes. In addition, DFT calculations have been performed to model the different complexation environments and simulate their electronic properties. The complexes retain SCO properties in the solid state exhibiting both thermal- and …

Layered Molecule-Based Magnets Formed by Decamethylmetallocenium Cations and Two-Dimensional Bimetallic Complexes [MIIRuIII(ox)3]−(MII=;Mn, Fe, Co, Cu and Zn; ox=oxalate)

Abstract A new series of hybrid organometallic-inorganic layered magnets with formula [Z III Cp * 2 ] [M II Ru III (ox) 3 ] ( Z III =Co and Fe; M II =Mn, Fe, Co, Cu, and Zn; ox=oxalate: Cp * =pentamethylcyclopentadienyl) has been prepared. All of these compounds are isostructural to the previously reported [ Z III Cp * 2 ] [ M II M III (ox) 3 ] ( M III =Cr, Fe) series and crystallize in the monoclinic space group C 2/ m , as found by powder X-ray diffraction analysis. They are novel examples of magnetic materials formed by bimetallic oxalate-based extended layers separated by layers of organometallic cations. The magnetic properties of all these compounds have been investigated (ac and dc m…

Mn 12 single-molecule magnets incorporated into mesoporous MCM-41 silica

Abstract The incorporation of four Mn12 derivatives, namely [Mn12O12(O2CR)16(H2O)4] (R=CH3 (1), CH3CH2 (2), C6H5 (3), C6F5 (4)), into the hexagonal channels of the MCM-41 mesoporous silica have been studied. Only the smallest clusters 1 and 2 that are those with compatible size with the pores of MCM-41 could be incorporated into the mesoporous silica. Powder X-ray diffraction (XRD) analysis and N2 adsorption–desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn12 clusters are inside the pores. The magnetic properties of the MCM-41/1 nanocomposite material indicate that the structure of the cluster is maintained after incorporat…

MOKE magnetometry as a probe of surface magnetic impurities in electropolymerized magnetic thin films of the Prussian blue analogue Fe3[Cr(CN)6]2·15 H2O

A magneto-optical Kerr effect (MOKE) study has been performed on electrodeposited thin films of the Prussian blue analogue Fe3[Cr(CN)6]2·15H2O (1). This study reveals the onset of hysteretic magnetic signals at temperatures above 60 K, in contrast with magnetic susceptibility measurements which indicate a Curie temperature of 23 K for this ferromagnetic film. The origin of this discrepancy is due to the presence of amorphous iron oxide particles that accumulate in the surface of the material. This report illustrates the potential of MOKE magnetometry for the detection of surface chemical impurities that remain elusive using bulk magnetic techniques.

Bottom‐Up Fabrication of Semiconductive Metal-Organic Framework Ultrathin Films

Though generally considered insulating, recent progress on the discovery of conductive porous metal-organic frameworks (MOFs) offers new opportunities for their integration as electroactive components in electronic devices. Compared to classical semiconductors, these metal-organic hybrids combine the crystallinity of inorganic materials with easier chemical functionalization and processability. Still, future development depends on the ability to produce high-quality films with fine control over their orientation, crystallinity, homogeneity, and thickness. Here self-assembled monolayer substrate modification and bottom-up techniques are used to produce preferentially oriented, ultrathin, con…

The Series of Molecular Conductors and Superconductors ET4[AFe(C2O4)3]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C2O4)2– = oxalate; A+ = H3O+, K+; X = F, Cl, Br, and I): Influence of the Halobenzene Guest Molecules on the Crystal Structure and Superconducting Properties

An extensive series of radical salts formed by the organic donor bis(ethylenedithio)tetrathiafulvalene (ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C(2)O(4))(3)](3-), and halobenzene guest molecules has been synthesized and characterized. The change of the halogen atom in this series has allowed the study of the effect of the size and charge polarization on the crystal structures and physical properties while keeping the geometry of the guest molecule. The general formula of the salts is ET(4)[A(I)Fe(C(2)O(4))(3)]·G with A/G = H(3)O(+)/PhF (1); H(3)O(+)/PhCl (2); H(3)O(+)/PhBr (3), and K(+)/PhI (4), (crystal data at room temperature: (1) monoclinic, space group C2/c with a = 1…

Organometallic Magnetic Materials

This chapter focuses on organometallic magnetic materials. It discusses the magnetic charge transfer salts based on metallocenes and hybrid magnets containing metallocenes. Polynuclear magnetic molecules based on metallocenes are also covered.

Molecular spins for quantum computation

Spins in solids or in molecules possess discrete energy levels, and the associated quantum states can be tuned and coherently manipulated by means of external electromagnetic fields. Spins therefore provide one of the simplest platforms to encode a quantum bit (qubit), the elementary unit of future quantum computers. Performing any useful computation demands much more than realizing a robust qubit—one also needs a large number of qubits and a reliable manner with which to integrate them into a complex circuitry that can store and process information and implement quantum algorithms. This ‘scalability’ is arguably one of the challenges for which a chemistry-based bottom-up approach is best-s…

Sublimable Single Ion Magnets Based on Lanthanoid Quinolinate Complexes: The Role of Intermolecular Interactions on Their Thermal Stability

We report the design, preparation, and characterization of two families of thermally robust coordination complexes based on lanthanoid quinolinate compounds: [Ln(5,7-Br2q)4]− and [Ln(5,7-ClIq)4]−, where q = 8-hydroquinolinate anion and Ln = DyIII, TbIII, ErIII, and HoIII. The sodium salt of [Dy(5,7-Br2q)4]− decomposes upon sublimation, whereas the sodium salt of [Dy(5,7- ClIq)4]−, which displays subtly different crystalline interactions, is sublimable under gentle conditions. The resulting film presents low roughness with high coverage, and the molecular integrity of the coordination complex is verified through AFM, MALDI-TOF, FT-IR, and microanalysis. Crucially, the single-molecule magnet …

Magnetic and electronic phase transitions probed by nanomechanical resonators

The reduced dimensionality of two-dimensional (2D) materials results in characteristic types of magnetically and electronically ordered phases. However, only few methods are available to study this order, in particular in ultrathin insulating antiferromagnets that couple weakly to magnetic and electronic probes. Here, we demonstrate that phase transitions in thin membranes of 2D antiferromagnetic FePS3, MnPS3 and NiPS3 can be probed mechanically via the temperature-dependent resonance frequency and quality factor. The observed relation between mechanical motion and antiferromagnetic order is shown to be mediated by the specific heat and reveals a strong dependence of the Néel temperature of…

Layered double hydroxide (LDH)–organic hybrids as precursors for low-temperature chemical synthesis of carbon nanoforms

A low-temperature route for the chemical synthesis of diverse carbon nanoforms, including nano-onions and multi-walled nanotubes, is described. The method involves thermal decomposition of a sebacate-intercalated NiFe LDH at 400 °C and benefits from the catalytic activity of FeNi3 nanoparticles generated in situ.

Decoherence from dipolar interspin interactions in molecular spin qubits

The realization of spin-based logical gates crucially depends on magnetically coupled spin qubits. Thus, understanding decoherence when spin qubits are in close proximity will become a roadblock to overcome. Herein, we propose a method free of fitting parameters to evaluate the qubit phase memory time ${T}_{m}$ in samples with high electron spin concentrations. The method is based on a model aimed to estimate magnetic nuclear decoherence [P. C. E. Stamp and I. S. Tupitsyn, Phys. Rev. B 69, 014401 (2004)]. It is applied to a ground-spin $J=8$ magnetic molecule 1 displaying atomic clock transitions, namely ${{[\mathrm{H}{\mathrm{o}}^{\mathrm{III}}{({\mathrm{W}}_{5}{\mathrm{O}}_{18})}_{2}]}^{9…

Synthesis and magnetic characterization of trans-dichloroplatinum blues with creatinine

Abstract By reaction of trans -[Pt II Cl 4 ] 2− with the amidate ligand creatinine two new paramagnetic blue platinum complexes have been obtained, namely violet and green varieties. These complexes have been characterized from thermal analysis, EPR and magnetic susceptibility. The violet complex has been formulated as trans -[Pt(creat)(H 2 O)Cl] 4 Cl. This compound has shown to be very stable, showing an extensive hyperfine structure in the powder EPR spectra. This result is a clear evidence of a tetranuclear oligomeric structure with one delocalized unpaired spin in the unit. EPR spectra in frozen solutions indicate that this mixed-valence complex maintains its oligomeric structure upon d…

Magnetic excitations in polyoxometalate tetrameric clusters

Abstract The metal-oxide clusters with formula [M4(D2O)2(PW9O34)2]10− which contain a tetrameric magnetic cluster M4O16 provide an ideal series for the study of magnetic exchange interactions in polymetallic molecular clusters. To get a more direct information on the splitting of the spin states caused by the exchange interactions we have performed inelastic neutron scattering measurements on the Co, Mn and Ni clusters. Magnetic excitations have been observed in the range 0.5–6 meV. A tentative interpretation of these data from a Heisenberg exchange Hamiltonian and a single ion zero-field splitting is presented for Ni cluster.

Binding Sites, Vibrations and Spin-Lattice Relaxation Times in Europium(II)-Based Metallofullerene Spin Qubits.

Abstract To design molecular spin qubits with enhanced quantum coherence, a control of the coupling between the local vibrations and the spin states is crucial, which could be realized in principle by engineering molecular structures via coordination chemistry. To this end, understanding the underlying structural factors that govern the spin relaxation is a central topic. Here, we report the investigation of the spin dynamics in a series of chemically designed europium(II)‐based endohedral metallofullerenes (EMFs). By introducing a unique structural difference, i. e. metal‐cage binding site, while keeping other molecular parameters constant between different complexes, these manifest the ke…

Modeling the properties of lanthanoid single-ion magnets using an effective point-charge approach

Herein, we present two geometrical models based on an effective point-charge approach to provide a full description of the lowest sublevels in lanthanoid single ion magnets (SIMs). The first one, named as the Radial Effective Charge (REC) model, evaluates the crystal field effect of spherical ligands, e.g. F(-), Cl(-) or Br(-), by placing the effective charge along the Ln-ligand axes. In this case the REC parameters are obtained fitting high-resolution spectroscopic data for lanthanoid halides. The second model, named as the Lone Pair Effective Charge (LPEC) model, has been developed in order to provide a realistic description of systems in which the lone pairs are not pointing directly tow…

Alternating antiferromagnetic and ferromagnetic exchange interactions in the S = 1 Heisenberg chain. Theory and magnetic properties

Abstract We focus on the magnetic properties of the S = 1 Heisenberg chain with alternating antiferromagnetic and ferromagnetic exchange interactions J 1 and J 2 . The magnetic behavior of this system is calculated as a function of the alternation parameter α = J 2 /| J 1 |, from a general numerical procedure based on closed spin chains of increasing length. These theoretical results are fitted to rational unified expressions, which are subsequently used to describe the magnetic behavior of a nickel (II) complex, [Ni(bipy)(N 3 ) 2 ] n , exhibiting an alternating chain structure with a dominant ferromagnetic exchange.

Synthesis, Crystal Structure, Thermal Analysis and Magnetic Behavior of a Novel One‐Dimensional Polymeric Pyridinium Chlorocuprate( II ): (Hpy) 2 [Cu 3 Cl 8 (H 2 O) 2 ]

A one-dimensional polymeric pyridinium chlorocuprate (HPy)2[Cu3Cl8(H2O)2], an intermediate between (HPy)CuCl3 and CuCl2·2H2O, has been synthesized and characterized by X-ray analysis [monoclinic, P21/c, a = 7.8950(10), b = 14.144(2), c = 9.921(10) A, β = 99.20(2)°]. The structure contains [Cu3Cl8(H2O)2]n2n− chains in which both square-pyramidal and octahedral CuII exist. The chains are composed of linked [Cu2Cl6]2− dimers and CuCl2(H2O)2 monomeric units. On being heated in the solid state the compound undergoes dehydration followed by dehydrohalogenation to produce a pyridine complex of CuII: [Cu3Py2Cl6]. Other compounds, (HPy)2[CuCl4], CuPyCl2 and CuPy2Cl2, also produce [Cu3Py2Cl6] as an i…

Synthesis, structure and magnetic characterization of [Fe(bpp)2][Cu(pds)2]2·solv (solv=CH3CN and CH3OH)

A novel salt of the Fe(II) cation [Fe(bpp)2]2+ (bpp = 2,6-bis(pyrazol-3-yl)pyridine) with the [CuIII(pds)2]- anion (pds = pirazine-2,3-diselenolate) formulated as [Fe(bpp)2][Cu(pds)2]2·3CH3CN has been prepared and characterized by single crystal X-ray diffraction and magnetic measurements. The salt presents a layered structure where cations and anions alternate along the b direction with many intermolecular short contacts between the cations and anions. The magnetic properties show that the Fe(II) cations [Fe(bpp)2]2+ present a high-spin S = 2 ground spin state with g = 2.073(1) and a zero field splitting (ZFS) of 7.7(1) cm-1 but no the expected spin transition at low temperatures. © 2008 E…

Crystal Engineering of Multifunctional Molecular Materials

In this paper we will focus on the crystal engineering of molecular materials exhibiting magnetic and/or electrical properties. The complexity of these materials needs of a precise design of the molecular building blocks, a control of the intermolecular interactions (hydrogen bonds, host/guest interactions, etc.) and a mastery in crystallization techni- ques in order to design crystal structures exhibiting useful physical proper- ties. We will illustrate this concept through some relevant examples based on two-component hybrid materials.

Crystallisation of H3BTC, H3TPO or H2SDA with MII (M = Co, Mn or Zn) and 2,2′-bipyridyl: design and control of co-ordination architecture, and magnetic properties (H3BTC = benzene-1,3,5-tricarboxylic acid, H3TPO = tris(4-carboxylphenyl)phosphine oxide, H2SDA = cis-stilbene-4,4′-dicarboxylic acid) †

The hydrothermal reaction of benzene-1,3,5-tricarboxylic acid (H3BTC) with MII (M = Mn, Co or Zn), tris(4-carboxyphenyl)phosphine oxide (H3TPO) or cis-stilbene-4,4′-dicarboxylic acid (H2SDA) with CoII and 2,2′-bipyridyl (BIPY) gave 1-D co-ordination networks formulated as: [M(HBTC)(BIPY)(H2O)] (M = Mn 1, Co 2, or Zn 3; [Co3(BTC)2(BIPY)2(H2O)6]·4H2O 4, [Co3(TPO)2(BIPY)2(H2O)6]·xH2O 5 and [Co(SDA)(BIPY)(H2O)] 6. Structures 1 and 2 consist of double stranded chains of alternating HBTC dianions and dimeric units MII–MII linked by two µ-(1,1) bridging carboxylates. Magnetic properties of 1 and 2 indicate the presence of ferromagnetic exchange interactions within the dimers. Structures 4 and 5 co…

One-dimensional and two-dimensional anilate-based magnets with inserted spin-crossover complexes.

The syntheses, structures, and magnetic properties of a family of bimetallic anilate-based compounds with inserted spin-crossover cationic complexes are reported. The structures of 1-4 present a two-dimensional anionic network formed by Mn(II) and Cr(III) ions linked through anilate ligands with inserted [Fe(III)(sal2-trien)](+) (1), [Fe(III)(4-OH-sal2-trien)](+) (2), [Fe(III)(sal2-epe)](+) (3), or [Fe(III)(5-Cl-sal2-trien)](+) (4) complexes. The structure of 5 is formed by anionic [Mn(II)Cl2Cr(III)(Cl2An)3](3-) chains surrounded by [Fe(II)(tren(imid)3)](2+), Cl(-), and solvent molecules. The magnetic properties indicate that 1-4 undergo a long-range ferrimagnetic ordering at ca. 10 K. On t…

Small-pore driven high capacitance in a hierarchical carbon via carbonization of Ni-MOF-74 at low temperatures

A hierarchical porous carbon prepared via direct carbonization of Ni-MOF-74 loaded with furfuryl alcohol at 450 °C displays high specific capacitance in comparison with other MOF-derived carbons as a result of the formation of micropores smaller than 1 nm.

Electrically switchable magnetic molecules: inducing a magnetic coupling by means of an external electric field in a mixed-valence polyoxovanadate cluster.

International audience; Herein we evaluate the influence of an electric field on the coupling of two delocalized electrons in the mixed-valence polyoxometalate (POM) [GeV14 O40 ](8-) (in short V14 ) by using both a t-J model Hamiltonian and DFT calculations. In absence of an electric field the compound is paramagnetic, because the two electrons are localized on different parts of the POM. When an electric field is applied, an abrupt change of the magnetic coupling between the two delocalized electrons can be induced. Indeed, the field forces the two electrons to localize on nearest-neighbors metal centers, leading to a very strong antiferromagnetic coupling. Both theoretical approaches have…

Spin-lattice relaxation via quantum tunneling in anEr3+-polyoxometalate molecular magnet

We investigate the mechanism of spin-lattice relaxation of Er ions encapsulated in polyoxometalate clusters, which below 4 K can only reverse its spin via quantum tunneling processes. The temperature-independent rate −1 is, at zero field, ten orders of magnitude larger than the rates predicted for direct phonon-induced processes. In addition, we observe that −1 is suppressed by external magnetic bias and hyperfine interactions but enhanced by increasing the concentration of Er ions. The observed relaxation agrees with predictions for pure quantum tunneling, showing that this phenomenon drives the thermalization of electronic spins. A possible link between these two phenomena is discussed, i…

Hybrid molecular materials for optoelectronic devices

Hybrid molecular materials based on semiconductor nanocrystalline metal oxides are a subject of intense research for the development of optoelectronic devices. Such devices follow the strategy of combining high surface area mesoporous materials with optically and electrochemically active molecules. Photovoltaic devices, molecular sensors and biosensors are some of the examples discussed in this paper.

Air stable hybrid organic-inorganic light emitting diodes using ZnO as the cathode

An air stable hybrid organic-inorganic light emitting device is presented. This architecture makes use of metal oxides as charge injecting materials into the light emitting polymer, avoiding the use of air sensitive cathodes commonly employed in organic light emitting diode manufacturing. We report the application of zinc oxide as a cathode in an organic light emitting device. This electroluminescent device shows high brightness levels reaching 6500 cd/m2 at voltages as low as 8 V. Compared to a conventional device using low workfunction metal cathodes, our device shows a lower turn-on voltage and it can operate in air.

Large-scale Nanopatterning of Single Proteins used as Carriers of Magnetic Nanoparticles

4 páginas, 4 figuras.

Vibronic Relaxation Pathways in Molecular Spin Qubit Na9[Ho(W5O18)2]·35H2O under Pressure

In order to explore how spectral sparsity and vibronic decoherence pathways can be controlled in a model qubit system with atomic clock transitions, we combined diamond anvil cell techniques with synchrotron-based far infrared spectroscopy and first-principles calculations to reveal the vibrational response of Na9[Ho(W5O18)2]&middot;35H2O under compression. Because the hole in the phonon density of states acts to reduce the overlap between the phonons and f manifold excitations in this system, we postulated that pressure might move the HoO4 rocking, bending, and asymmetric stretching modes that couple with the MJ = &plusmn;5, &plusmn;2, and &plusmn;7 levels out of resonance, reducing their …

Defect-Free Chemical Functionalization of Magnetic Monolayers Based on Coordination Polymers

&lt;p&gt;Chemical functionalization has demonstrated to be a powerful approach to tailor the physical and chemical properties of two-dimensional (2D) materials, to increase their processability and&lt;/p&gt; &lt;p&gt;stability, to add new functionalities and, even, to create new 2D materials. However, this post synthetic method – which involves the anchoring of molecules on the surface of an exfoliated 2D crystal – inevitably leads to defective materials, which lack long-range structural order. If defect-free functionalized monolayers are required, a radically new approach needs to be developed. Here we present a pre-synthetic method based on coordination chemistry that affords the isolatio…

Enhancing the electrocatalytic activity and stability of Prussian blue analogues by increasing their electroactive sites through the introduction of Au nanoparticles

Prussian blue analogues (PBAs) have been proven as excellent Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) in acidic, neutral and alkaline media. Further improvements can be achieved by increasing their electrical conductivity, but scarce attention has been paid to quantify the electroactive sites of the electrocatalyst when this enhancement occurs. In this work, we have studied how the chemical design influences the specific density of electroactive sites in different Au-PBA nanostructures. Thus, we have first obtained and fully characterized a variety of monodisperse core@shell hybrid nanoparticles of Au@PBA (PBA of NiIIFeII and CoIIFeII) with different shell siz…

Rational Design of Lanthanoid Single-Ion Magnets: Predictive Power of the Theoretical Models

We report two new single‐ion magnets (SIMs) of a family of oxydiacetate lanthanide complexes with D3 symmetry to test the predictive capabilities of complete active space ab initio methods (CASSCF and CASPT2) and the semiempirical radial effective charge (REC) model. Comparison of the theoretical predictions of the energy levels, wave functions and magnetic properties with detailed spectroscopic and magnetic characterisation is used to critically discuss the limitations of these theoretical approaches. The need for spectroscopic information for a reliable description of the properties of lanthanide SIMs is emphasised. SPINMOL ERC-CoG-647301 DECRESIM MAT2014-56143-R CTQ2014-52758-P CTQ2011-2…

Cobalt Clusters with Cubane-Type Topologies Based on Trivacant Polyoxometalate Ligands.

Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV-vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)](4-) (1) consists of a trilacunary [B-α-PW9O34](9-) unit which accommodates a cubane-like {Co(II)4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2](9-) (2), [Co7(OH)6(H2O)4(PW9O34)2]n(9n-) (3), and [Co7(OH)6(H2O)6(P2W15O56)2](15-) (4), dicubane-like {Co(II)6Co(III)O8} cores are encapsulated between two heptadentate [B…

Structural Transformations and Magnetic Effects Induced by Solvent Exchange in the Spin Crossover Complex [Fe(bpp) 2 ][Cr(bpy)(ox) 2 ] 2

Structural, thermal, magnetic and solvent-exchange properties of the spin crossover compound [Fe(bpp)2][Cr(bpy)(ox)2]2 containing paramagnetic anions are given. This complex salt 1 crystallises as a dihydrate with two inequivalent (high-spin and low-spin) FeII sites. The dehydrated compound is a spin-crossover material with T1/2 ↑ = 369 K and T1/2 ↓ = 353 K. Rehydration takes place without loss of crystallinity, yielding a polymorph (2) with 100 % high-spin Fe II sites. The different high-spin fractions in 1 and 2 have been correlated to structural changes in the FeII second coordination sphere. The magnetic response to the presence of different sorbed molecules has also been explored. © Wi…

Photophysical Properties of Oligo(phenylene ethynylene) Iridium(III) Complexes Functionalized with Metal-Anchoring Groups

[EN] The electrochemical and photophysical properties of a family of conjugated ligands and their iridium(III) cyclometallated complexes are described. They consist of a series of monocationic Ir-III bis-2-phenylpyridine complexes with p-phenylethynyl-1,10-phenanthroline ligands of different length. The structure of these ligands includes terminal acetylthiol or pyridine groups, which can provide good electrical contacts between metal electrodes. Cyclic voltammetry, absorption and emission spectroscopy, laser flash photolysis and density functional theory calculations reveal that the high conjugation of the diimine ligand affords small energy gaps between the frontier orbitals. Nevertheless…

Effect of Nonconstituent Additive Ions on the Controlled Crystallization of Lanthanide-Based Preyssler Polyoxometalates

Preyssler-type polyoxometalates (POMs) encapsulating lanthanide ions have been shown to provide ideal examples of single-molecule magnets and spin-qubits. However, the advances in this area are limited by the quality and size of the crystals. In this work, the role of additives ions in the crystallization of these POMs from aqueous solutions has been investigated. More specifically, we have studied the influence of Al3+, Y3+, and In3+ on the crystallization process of K12[MP5W30O110] (where M = Gd and Y). The results show that the concentration of these ions in the solution plays an important role in controlling the crystallization rate of the grown POM crystals leading to a significant inc…

Controlling the dimensionality of oxalate-based bimetallic complexes: The ferromagnetic chain {[K(18-crown-6)][Mn(bpy)Cr(ox)3]}∞(18-crown-6=C12H24O6, , bpy=C10H8N2)

Abstract The bimetallic ferromagnetic chain {[K(18-crown-6)][Mn(bpy)Cr(ox)3]}∞ (1) has been synthesized and characterized. It crystallizes in the orthorhombic chiral space group P212121 [a = 9.0510(2) A, b = 14.4710(3) A, c = 26.8660(8) A, V = 3510.97(1) A3, Z = 2]. Compound 1 is made up by anionic [Mn(bpy)Cr(ox)3]− 1D chains and cationic [K(18-crown-6)]+ complexes. The magnetic exchange within the chain is ferromagnetic [J = +7.8(7) cm−1]. In the solid state, the ferromagnetic chains are well isolated magnetically and no long range magnetic ordering has been observed above 2 K.

Kinetic exchange Hamiltonian for orbitally degenerate ions

Abstract A new approach to the problem of the kinetic exchange for orbitally degenerate ions is developed. The highly anisotropic effective Hamiltonian is expressed in terms of unit irreducible tensor operators and spin operators. All parameters of the exchange Hamiltonian are expressed through relevant transfer integrals, crystal field and Racah parameters for the metal ions. As an example the edge-shared ( D 2 h ) bioctahedral cluster is discussed and some comments on the considerations of Anderson, Goodenough and Kanamori and McConnell are given.

Influence of Proton Conducting Cations on the Structure and Properties of 2D Anilate-Based Magnets

The syntheses, structures, magnetic, and proton conductivity properties of a family of bimetallic anilate-based compounds with inserted alkylammonium cations are presented. The structures of (Me2NH2)[MnIICrIII(Br2An)3]·2H2O (1), (Et2NH2)[MnIICrIII(Br2An)3] (2), (Et3NH)[MnIICrIII(Cl2An)3] (3), and [(Et)(i-Pr)2NH]-[MnIICrIII(Br2An)3]·(CHCl3)0.5·(H2O) (4) contain a 2D anionic network formed by Mn(II) and Cr(III) ions linked through anilate ligands. In 1, 2, and 3, the hexagonal holes of this network are occupied by Me2NH2+, Et2NH2+, or Et3NH+ cations. Interestingly, the small increase of size of the templating cation in 4 ([(Et)(i-Pr)2NH]+ in the place of Me2NH2+, Et2NH2+ or Et3NH+), gives ris…

Intercalation of decamethylferrocenium cations in bimetallic oxalate-bridged two-dimensional magnets

The structure and magnetic properties of novel hybrid molecule-based magnets formed by combination of two magnetically active sublattices, the bimetallic oxalatobridged honeycomb net [MnIIMIII(ox)3] (MII = Mn, Fe, Co, Cr, Ni, Cu; MIII = Cr, Fe) and the organometallic cation decamethylferrocenium, are reported. Clemente Leon, Miguel, Miguel.Clemente@uv.es ; Coronado Miralles, Eugenio, Eugenio.Coronado@uv.es ; Galan Mascaros, Jose Ramon, Jose.R.Galan@uv.es ; Gomez Garcia, Carlos Jose, Carlos.Gomez@uv.es

A new approach for the synthesis of magnetic materials based on nitroxide free radicals and inorganic coordination polymers

The use of nitronyl nitroxide (NN) radicals as spectators inside extended inorganic magnetic lattices is described. Two possibilities are presently being explored, namely, the design of oxalato-bridged bimetallic networks by using cationic NN radicals of the N-alkylpyridinium type as templating agents, and the design of bimetallic lattices based on hexacyanometalates and nickel(II) diaminocomplexes incorporating anionic NN radicals of the carboxyphenyl type.

A chiral molecular conductor: synthesis, structure, and physical properties of [ET]3[Sb2(L-tart)2].CH3CN (ET = bis(ethylendithio)tetrathiafulvalene; L-tart = (2R,3R)-(+)-tartrate).

The salt [ET](3)[Sb(2)(L-tart)(2)].CH(3)CN (1) has been obtained by electrocrystallization of the organic donor bis(ethylendithio)tetrathiafulvalene (ET or BEDT-TTF) in the presence of the chiral anionic complex [Sb(2)(L-tart)(2)](2-) (L-tart = (2R,3R)-(+)-tartrate). This salt crystallizes in the chiral space group P2(1)2(1)2(1) (a = 11.145(2) angstroms, b = 12.848(2) angstroms, c = 40.159(14) angstroms, V = 5750.4(14) angstroms(3), Z = 4) and is formed by alternating layers of the anions and of the organic radicals in a noncentrosymmetric alpha-type packing. This compound shows a room temperature electrical conductivity of approximately 1 S.cm(-1) and semiconducting behavior with an activa…

A Symmetry Adapted Approach to the Dynamic Jahn-Teller Problem

In this article we present a symmetry-adapted approach aimed to the accurate solution of the dynamic Jahn-Teller (JT) problem. The algorithm for the solution of the eigen-problem takes full advantage of the point symmetry arguments. The system under consideration is supposed to consist of a set of electronic levels \({\Gamma }_{1},{\Gamma }_{2}\ldots {\Gamma }_{n}\) labeled by the irreducible representations (irreps) of the actual point group, mixed by the active JT and pseudo JT vibrational modes \({\Gamma }_{1},{\Gamma }_{2}\ldots {\Gamma }_{f}\) (vibrational irreps). The bosonic creation operators b +(Γγ) are transformed as components γ of the vibrational irrep Γ. The first excited vibra…

Comparison among superconducting models for β″-ET4[(H3O)Fe(C2O4)3]·C6H5Br single crystals by scanning tunnelling spectroscopy

Single crystals of the novel superconductor beta ''-(BEDT-TTF)(4)[(H3O)Fe(C2O4)(3)]center dot C6H5Br charge-transfer salt were studied using a scanning tunnelling microscope. The measured samples have an onset critical temperature of about 4.0 K. Features often reported on similar compounds were observed in the tunnelling spectra at 1.4 K. STS spectra are compared with several models for the superconducting density of states. Our analysis evidences inhomogeneous superconductivity and indicates that the presence of a magnetic layer into the sample plays a role in determining the superconducting spectroscopic features. (C) 2008 Elsevier Masson SAS. All rights reserved.

Reversible tuning of luminescence and magnetism in a structurally flexible erbium-anilato MOF.

By combining 3,6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (H2trz2An) with NIR-emitting ErIII ion, two different 3D neutral polymorphic frameworks (1a and 1b), differing for the number of uncoordinated water molecules, formulated as [Er2(trz2An)3(H2O)4]n·xH2O (x = 10, a; x = 7, b), have been obtained. The structure of 1a shows layers with (6,3) topology forming six-membered rings with distorted hexagonal cavities along the bc plane. These 2D layers are interconnected through the N4 atoms of the two pendant arms of the trz2An linkers, leading to a 3D framework, where neighboring layers are eclipsed along the a axis, with hexagonal channels filled with water molecules. In 1b, layers with (…

Determining Key Local Vibrations in the Relaxation of Molecular Spin Qubits and Single-Molecule Magnets.

To design molecular spin qubits and nanomagnets operating at high temperatures, there is an urgent need to understand the relationship between vibrations and spin relaxation processes. Herein we develop a simple first-principles methodology to determine the modulation that vibrations exert on spin energy levels. This methodology is applied to [Cu(mnt)2]2– (mnt2– = 1,2-dicyanoethylene-1,2-dithiolate), a highly coherent complex. By theoretically identifying the most relevant vibrational modes, we are able to offer general strategies to chemically design more resilient magnetic molecules, where the energy of the spin states is not coupled to vibrations.

Not just size and shape: spherically symmetrical d5 and d10 metal ions give different coordination nets with 4,2′:6′,4″-terpyridines

Functionalized 4,2′:6′,4″-terpyridine ligands have been used to provide a divergent N,N′-donor set for the formation of coordination polymers containing {Zn2(µ-OAc)4} or {Mn3(µ-OAc)4(OAc)2} scaffolds. Single-stranded coordination polymers are produced from the reactions of 4′-(4-bromophenyl)-4,2′:6′,4″-terpyridine (1) and 4′-(4-methylthiophenyl)-4,2′:6′,4″-terpyridine (2) with Zn(OAc)2·2H2O. In [Zn2(1)(OAc)4]n and [Zn2(2)(OAc)4]n, the two outer nitrogen donors of the 4,2′:6′,4″-terpyridine ligands, bind to the axial sites of {Zn2(µ-OAc)4} units to generate coordination polymer chains which are π-stacked so that the V-shaped ligand domains are interleaved. When Mn(OAc)2·4H2O is treated with …

Synthesis, structure and magnetic properties of iron (II), cobalt (II) and nickel (II) complexes of 2,6-bis(pyrazol-3-yl)pyridine and paramagnetic counterions

Abstract Iron (II), cobalt (II) and nickel (II) complexes of 2,6-bis(pyrazol-3-yl)pyridine (bpp) with [Cr(C2O4)3]3− have been prepared. They were characterised by single-crystal X-ray diffraction, magnetic susceptibility measurements and thermal gravimetric analyses. All three compounds are isostructural and they are formed by isolated [MII(bpp)2]2+ and [Cr(C2O4)3]3− complexes and free ClO4 −. As expected, only the salt [Fe(bpp)2]2[Cr(C2O4)3]ClO4·5H2O shows a thermal spin transition with transition temperature (T1/2) around 375 K that is correlated to the loss of water molecules.

Photo-induced magnetic bistability in a controlled assembly of anisotropic coordination nanoparticles.

International audience; Anisotropic coordination nanoparticles of the photomagnetic network Cs(I)(2)Cu(II)(7)[Mo(IV)(CN)(8)](4) are obtained through a surfactant-free high-yield synthetic procedure in water. These particles are organised as Langmuir-Blodgett films with a preferential orientation of the nano-objects within the film that exhibit a magnetic bistability below 20 K with a very large coercivity due to an efficient photo-transformation.

Hybrid organic-inorganic light emitting diodes: effect of the metal oxide

Hybrid organic-inorganic light emitting diodes (HyLEDs), employing metal oxides as the electron injecting contacts, are interesting as an alternative to OLEDs. Until recently, the metal oxide of choice was either titanium dioxide or zinc oxide. In this work two wide bandgap metal oxides, HfO2 and MgO, are employed as electron injecting layer in HyLEDs. It is demonstrated that both the current density and the luminance values obtained are directly related to the barriers for electron injection (from the ITO to the metal oxide) and for hole transfer to the same metal oxide, outlining a new design rule for the optimization of HyLEDs. Record device efficacies (3.3 cd/A, >10000 cd/m2) using the …

Layered gadolinium hydroxides for low-temperature magnetic cooling

Layered gadolinium hydroxides have revealed to be excellent candidates for cryogenic magnetic refrigeration. These materials behave as pure 2D magnetic systems with a Heisenberg-Ising critical crossover, induced by dipolar interactions. This 2D character and the possibility offered by these materials to be delaminated open the possibility of rapid heat dissipation upon substrate deposition.

A Molecular Metal Ferromagnet from the Organic Donor Bis(ethylenedithio)tetraselenafulvalene and Bimetallic Oxalate Complexes

A new dual-function hybrid molecular material has been obtained from the organic donor bis(ethylenedithio)tetraselenafulvalene and the honeycomb oxalate-based bimetallic network [MnCr(ox)3]-. This multilayer material consists of layers of the inorganic anionic 2D network, responsible for the appearance of ferromagnetic ordering below 5.3 K, alternating with segregated layers of the organic cation radical responsible for the transport properties:  metal-like conductivity is observed from room temperature down to 150 K.

Coexistence of Mobile and Localized Electrons in Bis(ethylene)dithiotetrathiafulvalene(BEDT-TTF) Radical Salts with Paramagnetic Polyoxometalates: Synthesis and Physical Properties of(BEDT-TTF)8[CoW12O40]· 5.5 H2O

Spin polarization in electrodeposited thin films of the molecule-based magnetic semiconductor Cr5.5(CN)12·11.5H2O

The magnetoresistance (MR) effect of thin films of the Prussian Blue Analogue (PBA) Cr5.5(CN)12·11.5H2O, prepared by electrochemical deposition, has been measured using the standard two-point probe method. This molecule-based ferrimagnetic material, with a Tc = 240 K, exhibits MR up to 2% at 6 T and 200 K.

Pressure-tuning of magnetism and linkage isomerism in iron(II) hexacyanochromate.

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)-iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8 square1.2.16H2O (1). Upon application of pressure in the 0-1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic inte…

Photoinduced effects on the magnetic properties of the (Fe0.2Cr0.8)1.5[Cr(CN)6] Prussian blue analogue

International audience; One of the most attractive characteristics of some Prussian blue derivatives is the sensitivity of their magnetic properties to the irradiation with light. In this work photoinduced effects in the (Fe0.2Cr0.8)1.5[Cr(CN)6]·15H2O PBA have been studied by means of X-ray-based spectroscopies and magnetometry. It is found that the photosensitivity of this compound is mostly centred on the Fe cations: the exposure to green light induces a transfer of electrons from them to the Cr that provokes a reversal of the previously existing linkage isomerization and increases the elastic strain caused by the misfit of the unit cells of the Fe–NC–Cr and Cr–NC–Cr sublattices. The gree…

Synthesis, Structure, Spectroscopic Studies and Magnetic Properties of the Tetrakis(5,7‐dichloro‐8‐quinolinolato)gadolinium(III) Complex

The synthesis and structural characterization of the neutral gadolinium tetrakis-type complex with 5,7-dichloro-8-quinolinolato (H5,7ClQ) ligands, [Gd(5,7ClQ)2(H5,7ClQ)2Cl], is reported. The GdIII ion is epta coordinated to one chloride ion and to four ligands: two N,O-chelated monoanions and two as zwitterionic (+NH and O–) monodentate oxygen donors. Electronic and vibrational spectra provide suitable markers to distinguish the presence of deprotonated and protonated ligands. The magnetic behaviour of this compound was investigated and explained by taking into account that π–π stacking interactions between the (H5,7ClQ) ligands give rise to a ferromagnetic interaction between the gadoliniu…

Hybrid Materials Formed by Two Molecular Networks. Towards Multiproperty Materials

Abstract The possibilities offered by hybrid materials formed by two molecular networks in the context of the molecular magnets are illustrated. Molecule-based layered magnets are used as anionic hosts for electroactive molecules, with the aim of obtaining multiproperty materials exhibiting in addition to the cooperative magnetism other interesting properties according to the nature of the inserted molecules. In particular, hybrid molecular compounds containing molecular species giving rise to paramagnetic, conducting, or bi-stable properties are reported.

Interface-Assisted Sign Inversion of Magnetoresistance in Spin Valves Based on Novel Lanthanide Quinoline Molecules

Molecules are proposed to be an efficient medium to host spin-polarized carriers, due to their weak spin relaxation mechanisms. While relatively long spin lifetimes are measured in molecular devices, the most promising route toward device functionalization is to use the chemical versatility of molecules to achieve a deterministic control and manipulation of the electron spin. Here, by combining magnetotransport experiments with element-specific X-ray absorption spectroscopy, this study shows the ability of molecules to modify spin-dependent properties at the interface level via metal–molecule hybridization pathways. In particular, it is described how the formation of hybrid states determine…

Ein neuartiges Polyoxowolframat mit einemtriangulo-NiII3-Cluster mit ferromagnetischen Austauschwechselwirkungen und einemS = 3-Grundzustand

Hybrid Organic/Inorganic Molecular Materials Formed by Tetrathiafulvalene Radicals and Magnetic Trimeric Clusters of Dimetallic Oxalate‐Bridged Complexes: The Series (TTF) 4 {M II (H 2 O) 2 [M III (ox) 3 ] 2 }· n H 2 O (M II = Mn, Fe, Co, Ni, Cu and Zn; M III = Cr and Fe; ox = C 2 O 4 2− )

The first examples of trimeric, dimetallic, pure oxalate-bridged complexes [ox = (C2O4)2−] have been synthesized and characterized structurally and magnetically for the two new series of crystalline molecular assemblies formulated as (TTF)4{MII(H2O)2[MIII(ox)3]2}·nH2O [for MIII = Cr; MII = Mn (1), Fe (2), Co (3), Ni (4), Cu (5) and Zn (6); for MIII = Fe; MII = Mn (7), Fe (8), Co (9), Ni (10) and Zn (11)]. Both series (Cr2M and Fe2M) are isostructural. The crystal structure of (TTF)4{Mn(H2O)2[Cr(ox)3]2}⋅14H2O (1) [monoclinic, space group C2/c (no. 15), a = 13.240(5) A, b = 19.450(5) A, c = 27.690(5) A, β = 97.63(5)°, V = 7068(3) A3 and Z = 4] shows alternating layers of the organic radical T…

Cover Feature: The Missing Link in the Magnetism of Hybrid Cobalt Layered Hydroxides: The Odd–Even Effect of the Organic Spacer (Chem. Eur. J. 3/2021)

Bistable spin-crossover nanoparticles showing magnetic thermal hysteresis near room temperature

We have demonstrated that the reverse micelle technique can be applied to polymeric spin-crossover systems, such as [Fe(Htrz)2(trz)](BF4), to control the growth of the crystallites. Small nanoparticles of diameters around 10 nm and narrow size distribution were obtained. It is easy to envision that, by modifying the synthetic procedure, the size and critical temperatures of these nanoparticles can be tuned. On one hand, different ratios of solvent, water, and surfactants will lead to different micelle sizes, which will affect the particle size and, maybe, the magnetic properties. On the other hand, the critical temperatures can be lowered towards room temperature by changing the composition…

Fe(II) spin crossover complexes of a derivative of 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) functionalized with a carboxylic acid in the 3-pyridyl position

Abstract The preparation of a new bis(pyrazol-1-yl)pyridine (1-bpp) derivative functionalized with a carboxylic acid in the 3-pyridyl position, bpp3-COOH ligand is reported together with the structure and spin-crossover (SCO) properties of [FeII(bpp3-COOH)2](ClO4)2·0.5EtOH·0.5H2O (1). Magnetic properties of 1 indicate that LS is favored. Desolvation leads to a gradual and incomplete SCO. Solvated and desolvated compounds show LIESST effect.

Quantum Phases and Spin Liquid Properties of 1T-TaS2

Quantum materials exhibiting magnetic frustration are connected to diverse phenomena including high-Tc superconductivity, topological order and quantum spin liquids (QSLs). A QSL is a quantum phase (QP) related to a quantum-entangled fluid-like state of matter. Previous experiments on QSL candidate materials are usually interpreted in terms of a single QP, although theories indicate that many distinct QPs are closely competing in typical frustrated spin models. Here we report on combined temperature-dependent muon spin relaxation and specific heat measurements for the triangular-lattice QSL candidate material 1T-TaS2 that provide evidence for competing QPs. The measured properties are assig…

Alkoxide-intercalated NiFe-layered double hydroxides magnetic nanosheets as efficient water oxidation electrocatalysts

Alkoxide-intercalated NiFe-layered double hydroxides were synthesized via the nonaqueous methanolic route. These nanoplatelets exhibit high crystalline quality as demonstrated by atomic resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Moreover, the presence of the alkoxide moieties has been unambiguously demonstrated by means of thermogravimetric analysis coupled to a mass spectrometer. These NiFe-LDHs can be exfoliated in water or organic solvents and processed into homogeneous ultra-thin films (&lt; 3nm thick) with the assistance of O2-plasma. The study of their behaviour as water oxidation electrocatalysts has shown an outstanding perf…

Quantum Rescaling, Domain Metastability, and Hybrid Domain‐Walls in 2D CrI3 Magnets

Higher-order exchange interactions and quantum effects are widely known to play an important role in describing the properties of low-dimensional magnetic compounds. Here, the recently discovered 2D van der Waals (vdW) CrI3 is identified as a quantum non-Heisenberg material with properties far beyond an Ising magnet as initially assumed. It is found that biquadratic exchange interactions are essential to quantitatively describe the magnetism of CrI3 but quantum rescaling corrections are required to reproduce its thermal properties. The quantum nature of the heat bath represented by discrete electron-spin and phonon-spin scattering processes induces the formation of spin fluctuations in the …

Molecule-based ferromagnetic conductors: Strategy and design

The design and study of hybrid crystalline solids in the search for multifunctional materials is one of the most appealing possibilities where molecule-based materials offer striking advantages: from the combination of molecular building blocks with the desired tailor-made chemical and physical properties. In this review we will cover all aspects of the so-called molecular ferromagnetic conductors, built from combination in a single compound of organic cationic radicals, able to give rise to conducting architectures, with polymeric anionic metal complexes, able to give rise to ferromagnetism. The relevant successes and drawbacks of this approach will be highlighted and discussed in detail.

A New Layered Compound Containing [PMo12O40]3- and Both 5- and 6-Coordinated Homoleptic (1-(2-Chloroethyl)tetrazole)Copper(II) Cations

The synthesis, crystal structure and physical properties of the complex obtained from the reaction between the polyoxometalate anion [PMo12O40]3- copper(II) and the ligand 1-(2-chloroethyl)tetrazole (teec) are described. This compound has been synthesized as a model for designing materials containing both magnetic polyoxometalate anions and iron(II) spin-crossover cations. Keywords. Coordination chemistry; Heterocycles; Polyoxometalates; Structure elucidation; Tetrazole.

Smart molecular/MoS2 Heterostructures Featuring Light and Thermally-Induced Strain Driven by Spin Switching

In this work we exploit the ability of spin-crossover molecules to switch between two spin states, upon the application of external stimuli, to prepare smart molecular/2D heterostructures. Through the chemical design of the hybrid interface, that involves a covalent grafting between the two components, we obtain a hybrid heterostructure formed by spin-crossover nanoparticles anchored on chemically functionalized monolayers of semiconducting MoS2. In the resulting hybrid, the strain generated by the molecular system over the MoS2 layer, as a consequence of a thermal or light-induced spin switching, results in a dramatic and reversible change of its electrical and optical properties. This nov…

Low-Frequency Imaginary Impedance at the Superconducting Transition of 2H - NbSe2

The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature ${T}_{c}$. A superconductor exactly at ${T}_{c}$ is thus very sensitive to all kinds of thermal perturbation, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizable imaginary impedance at frequencies of the order of tens of hertz at the resistive transition of single crystals of the layered material $2H$-${\mathrm{Nb}\mathrm{Se}}_{2}$. We explain the result using models developed for transition-edge sensors. By measuring under magnetic fields and at high cu…

A Comparative Structural and Magnetic Study of Three Compounds Based on the Cluster Unit M4Cl8(THF)6 (M=Mn, Fe, Co)

Treatment of anhydrous M Cl 2 phases with THF under refluxing conditions leads to excision of the clusters M 4 Cl 8 (THF) 6 ( M =Fe (1), Co (3)) and dimensional reduction to the chain of clusters, {Mn 4 Cl 8 (THF) 6 (Mn(THF) 2 Cl 2 } ∞ , (2). All three compounds were isolated in high yields as crystalline materials and subjected to comprehensive magnetic studies. X-ray structures of the three compounds were performed to verify the nature of the compounds, but only the Mn derivative is discussed in detail due to the fact that the structures of the Fe and Co clusters were reported earlier. The molecular structures of M 4 Cl 8 (THF) 6 ( M =Fe, Co) consist of a rhombic arrrangement of metal ion…

Inside Cover: A SIM-MOF: Three-Dimensional Organisation of Single-Ion Magnets with Anion-Exchange Capabilities (Chem. Eur. J. 34/2014)

Bimetallic Cyanide-Bridged Complexes Based on the Photochromic Nitroprusside Anion and Paramagnetic Metal Complexes. Syntheses, Structures, and Physical Characterization of the Coordination Compounds [Ni(en)2]4[Fe(CN)5NO]2[Fe(CN)6]·5H2O, [Ni(en)2][Fe(CN)5NO]·3H2O, [Mn(3-MeOsalen)(H2O)]2[Fe(CN)5NO], and [Mn(5-Brsalen)]2[Fe(CN)5NO]

The synthesis, crystal structure, and physical characterization of the coordination compounds [Ni(en)2]4[Fe(CN)5NO]2[Fe(CN)6]x5H2O (1), [Ni(en)2][Fe(CN)5NO]x3H2O (2), [Mn(3-MeOsalen)(H2O)]2[Fe(CN)5NO] (3), and [Mn(5-Brsalen)]2[Fe(CN)5NO] (4) are presented. 1 crystallizes in the monoclinic space group P2(1)/n (a = 7.407(4) A, b = 28.963(6) A, c = 14.744(5) A, alpha = 90 degrees, beta = 103.26(4) degrees, gamma = 90 degrees, Z = 2). Its structure consists of branched linear chains formed by cis-[Ni(en)2]2+ cations and ferrocyanide and nitroprusside anions. The presence of two kinds of iron(II) sites has been demonstrated by Mossbauer spectroscopy. 2 crystallizes in the monoclinic space group …

Role of Orbital Degeneracy in the Single Molecule Magnet Behavior of a Mononuclear High-Spin Fe(II) Complex

To explain the single-molecule magnet behavior of the mononuclear complex [(tpaMes)Fe](-) we have developed a model that takes into account the trigonal ligand field splitting of the atomic (5)D term of the Fe(II) ion, and the spin-orbital splitting and mixing of the ligand field terms. The ground ligand field term is shown to be the orbital doublet (5)E possessing an unquenched orbital angular momentum. We demonstrate that the splitting of this term cannot be described by the conventional zero-field splitting Hamiltonian proving thus the irrelevance of the spin-Hamiltonian formalism in the present case. The first-order orbital angular momentum is shown to lead to the strong magnetic anisot…

Controlling magnetism with light in zero orbital angular momentum antiferromagnet

Antiferromagnetic materials feature intrinsic ultrafast spin dynamics, making them ideal candidates for future magnonic devices operating at THz frequencies. A major focus of current research is the investigation of optical methods for the efficient generation of coherent magnons in antiferromagnetic insulators. In magnetic lattices endowed with orbital angular momentum, spin-orbit coupling enables spin dynamics through the resonant excitation of low-energy electric dipoles such as phonons and orbital resonances which interact with spins. However, in magnetic systems with zero orbital angular momentum, microscopic pathways for the resonant and low-energy optical excitation of coherent spin …

Controlling the anisotropy of a van der Waals antiferromagnet with light

Ultrafast optical control of magnetic anisotropy in a van der Waals antiferromagnet activates a sub-THz two-dimensional magnon.

Exchange-transfer in mixed-valence clusters with one migrating hole

Abstract A new mechanism for exchange-transfer specific to hole-type mixed-valence clusters is proposed. The intermediate state in the second-order exchange-transfer process is achieved by the jump of the electron from the spin-core of the dn+1 ion into the empty orbital of the dn ion. As distinguished from the mixed-valence clusters with one delocalized electron this intermediate state is the high-spin one giving rise to a ferromagnetic contribution to the ground manifold. On the basis of angular momentum theory a general solution of the exchange-transfer problem is given for arbitrary nuclearity mixed-valence hole-type clusters with many-electron paramagnetic spin-cores. The interplay bet…

Magnetic excitations in an exchange-coupled tetramer cluster of cobalt (II): a study by inelastic neutron scattering

Abstract The polyoxometalate K 10 [Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 ].20H 2 O contains a ferromagnetically exchange-coupled tetramer of Co 11 encapsulated in between two diamagnetic molecules (PW 9 O 34 -9 . At 2.5K several inelastic peaks are observed in the energy range 1.5–7 meV, which are assigned to magnetic excitations in the cluster. A tentative interpretation of these data from an anisotropic exchange model yields a cobalt-cobalt interaction of 3meV (24cm -1 ) and an amount of anisotropy J xy / J z ≌0.6. These values are consistent with the magnetic susceptibility measurements.

Magnetic polyoxometalates: anisotropic exchange interactions in the moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-.

The magnetic exchange interactions in a C0(3)(11) moiety encapsulated in Na(17) [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)] (NaCo(3)) were studied by a combination of magnetic measurements (magnetic susceptibility and low-temperature magnetization), with a detailed Inelastic Neutron Scattering (INS) investigation. The novel structure of the salt was determined by X-ray crystallography. The ferromagnetic Co(3)O(14) triangular cluster core consists of three octahedrally oxo-coordinated Co(II) ions sharing edges. According to the single-ion anisotropy and spin-orbit coupling usually assumed for octahedral Co(II) ions, the appropiate exchange Hamiltonian to describe the ground-state properties o…

Magnetic In-Tube Solid Phase Microextraction

We report a new in-tube solid phase microextraction approach named magnetic in-tube solid phase microextraction, magnetic-IT-SPME. Magnetic-IT-SPME has been developed, taking advantage of magnetic microfluidic principles with the aim to improve extraction efficiency of IT-SPME systems. First, a magnetic hybrid material formed by Fe(3)O(4) nanoparticles supported on SiO(2) was synthesized and immobilized in the surface of a bared fused silica capillary column to obtain a magnetic adsorbent extraction phase. The capillary column was placed inside a magnetic coil that allowed the application of a variable magnetic field. Acetylsalicylic acid, acetaminophen, atenolol, diclofenac, and ibuprofen …

Molecular analog of multiferroics: Electric and magnetic field effects in many-electron mixed-valence dimers

We show here that mixed-valence (MV) magnetic molecules with a significant electron delocalization are extremely sensitive to an external electric field. In particular, we focus on the symmetric many-electron MV binuclear complexes that are on the borderline between Robin and Day classes II and III. In these molecules, the double-exchange, which has been shown to lead to the ferromagnetic ground spin state, competes with the electric field, which tends to localize the spin, thus creating an electric dipole and stabilizing the spin states with lower multiplicities. This provides an efficient and easy way to control the ground spin state of the molecule through the double-exchange mechanism. …

Magnetic functionalities in MOFs: from the framework to the pore

In this review, we show the different approaches so far developed to prepare Metal-Organic Frameworks (MOFs) presenting electronic functionalities, with particular attention to magnetic properties. We will cover the chemical design of the framework necessary for the incorporation of different magnetic phenomena, as well as the encapsulation of functional species in the pores leading to hybrid multifunctional MOFs combining an extended lattice with a molecular lattice.

Iron(II) complex of 2-(1H-pyrazol-1-yl)pyridine-4-carboxylic acid (ppCOOH) suitable for surface deposition

The synthesis, structural and magnetic characterization of the tris iron(II) complex of 2-(1H-pyrazol-1-yl)pyridine-4-carboxylic acid (ppCOOH) ligand are reported in [Fe(ppCOOH)3](ClO4)2·0.5H2O·2EtOH. Single crystal structure and magnetic characterization of the bulk compound show that the low-spin state is dominant from 2 to 400 K. ESI-MS and UV–Vis spectroscopy experiments indicate that acetonitrile solutions of this complex are stable with time. ESI-MS confirms the presence of the tris complex in solution. This complex can be deposited onto SiO2 surfaces due to the presence of carboxylic acid groups by immersing the substrates into acetonitrile solutions of the complex. XPS spectra of th…

Synthesis, Chirality, and Magnetic Properties of Bimetallic Cyanide-Bridged Two-Dimensional Ferromagnets

The assembly of hexacyanoferrate(III) anions and nickel(II) bis-diamino complexes of the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) yields cyanide-bridged two-dimensional ferromagnets of the general formula [Ni(trans-chxn)2]3[Fe(CN)6]2‚2H2O. Their crystal structure is built from cyanide-bridged bimetallic planes separated by the bulky chxn ligands, giving rise to a large interlayer distance ( d ) 11.7 A). These materials order ferromagnetically at the Curie temperature TC ) 14 K. AC susceptibility measurements evidence an unusual magnetic behavior below TC, with a marked frequency dependence. A thorough magnetic analysis demonstrates that this complex behavior is due to the pi…

A Local Study of the Transport Mechanisms in MoS2 Layers for Magnetic Tunnel Junctions

MoS2-based vertical spintronic devices have attracted an increasing interest thanks to theoretical predictions of large magnetoresistance signals. However, experimental performances are still far from expectations. Here, we carry out the local electrical characterization of thin MoS2 flakes in a Co/Al2O3/MoS2 structure through conductive tip AFM measurements. We show that thin MoS2 presents a metallic behavior with a strong lateral transport contribution that hinders the direct tunnelling through thin layers. Indeed, no resistance dependence is observed with the flake thickness. These findings reveal a spin depolarization source in the MoS2-based spin valves, thus pointing to possible solut…

O-Doped Nanographenes: A Pyrano/Pyrylium Route Towards Semiconducting Cationic Mixed-Valence Complexes

Herein we report an efficient synthesis to prepare O‐doped nanographenes, which derive from the longitudinally and latitudinally p‐extension of pyrene. The derivatives are highly fluorescent and feature low‐oxidation potentials. Exploiting electrooxidation, crystals of cationic mixed valence (MV) complexes were grown in which the organic salts organize into face‐to‐face p‐ p stacks, a favorable solid‐state arrangement for organic electronics. Variable‐temperature EPR measurements and relaxation studies suggest a strong electron delocalization along the longitudinal axis of the columnar p‐stacking architectures. Electric measurements of single crystals of the MV salts exhibited a semiconduct…

Spin-crossover nanoparticles anchored on MoS2 layers for heterostructures with tunable strain driven by thermal or light-induced spin switching

In the past few years, the effect of strain on the optical and electronic properties of MoS2 layers has attracted particular attention as it can improve the performance of optoelectronic and spintronic devices. Although several approaches have been explored, strain is typically externally applied on the two-dimensional material. In this work, we describe the preparation of a reversible ‘self-strainable’ system in which the strain is generated at the molecular level by one component of a MoS2-based composite material. Spin-crossover nanoparticles were covalently grafted onto functionalized layers of semiconducting MoS2 to form a hybrid heterostructure. Their ability to switch between two spi…

Magnetic exchange interaction in clusters of orbitally degenerate ions. I. Effective Hamiltonian

Abstract A new effective Hamiltonian is reported for the kinetic exchange between two arbitrary terms 2S A +1 Λ A and 2S B +1 Λ B that can be ground or excited in octahedrally coordinated transition metal ions. This Hamiltonian is applicable to both homo- and heterometallic clusters. For the homonuclear cluster the resonance part of the effective Hamiltonian is also presented for the case when one of the ions is excited. The operator part of the exchange Hamiltonian contains symmetry adapted products of the cubic irreducible tensors acting in orbital spaces ΛA and ΛB and scalar product of site spin operators. The parameters of the Hamiltonian are defined by the relevant intercenter transfer…

Inorganic Materials and Ionic Liquids: Large-scale Nanopatterning of Single Proteins used as Carriers of Magnetic Nanoparticles (Adv. Mater. 5/2010)

Graphene related magnetic materials: micromechanical exfoliation of 2D layered magnets based on bimetallic anilate complexes with inserted [FeIII(acac2-trien)]+ and [FeIII(sal2-trien)]+ molecules

The syntheses, structures and magnetic properties of the coordination compounds of formula [FeIII(acac2-trien)][MnIICrIII(Cl2 An)3]·(CH3CN)2 (1), [FeIII(acac2-trien)][MnIICrIII(Br2An)3]·(CH3CN)2 (2) and [GaIII(acac2-trien)][MnIICrIII(Br2An)3]·(CH3CN)2 (3) are reported. They exhibit a 2D anionic network formed by Mn(II) and Cr(III) ions linked through anilate ligands, while the [FeIII(acac2-trien)]+ or [GaIII(acac2-trien)]+ charge-compensating cations are placed inside the hexagonal channels of the 2D network, instead of being inserted in the interlamellar spacing. Thus, these crystals are formed by hybrid layers assembled through van der Waals interactions. The magnetic properties indicate …

Graphene electrochemical responses sense surroundings

Abstract Graphite oxide (GO) paper, obtained by direct filtration of exfoliated GO in water over PTFE membrane filters, was reduced by using hydrazine vapours. The graphene-paper thus obtained was characterized by the combination of different techniques. The electrochemical characterization by cyclic voltammetry, chronoamperometry and chronopotentiometry presents a strong influence of the working conditions: temperature, electrolyte concentration and current on the electrochemical responses, indicating a good ability of the material to sense ambient and working conditions. Electrochemical devices based on graphene are expected to work as dual, and simultaneous, sensing-actuators.

Gas confinement in compartmentalized coordination polymers for highly selective sorption

Discrimination between different gases is an essential aspect for industrial and environmental applications involving sensing and separation. Several classes of porous materials have been used in this context, including zeolites and more recently MOFs. However, to reach high selectivities for the separation of gas mixtures is a challenging task that often requires the understanding of the specific interactions established between the porous framework and the gases. Here we propose an approach to obtain an enhanced selectivity based on the use of compartmentalized coordination polymers, named CCP-1 and CCP-2, which are crystalline materials comprising isolated discrete cavities. These compar…

Chiral charge order in the superconductor 2H-TaS(2)

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM

Dynamic magnetic materials based on the cationic coordination polymer [Cu(btix)2]n(2n+) [btix = 1,4-bis(triazol-1-ylmethyl)benzene]: tuning the structural and magnetic properties through anion exchange.

A three-dimensional coordination polymer, [Cu(btix)(2)(BF(4))(2)](n) [btix = 1,4-bis(triazol-1-ylmethyl)benzene], with antiferromagnetic interactions occurring via the organic ligand, has been prepared and characterized. It has been shown to permit the exchange of anionic species in the crystalline network with modification of the magnetic properties. Coordinated BF(4)(-) can be reversibly exchanged by different anions with (NO(3)(-) and Cl(-)) or without (PF(6)(-) and ClO(4)(-)) dynamic response of the organic ligand, which acts as the only linker between the metal centers. Interestingly, an irreversible exchange occurs with N(3)(-) anions to generate a new coordination polymer, [Cu(btix)(…

Assisted-assembly of coordination materials into advanced nanoarchitectures by Dip Pen nanolithography

3 páginas, 4 figuras.

Electric Field Generation and Control of Bipartite Quantum Entanglement between Electronic Spins in Mixed Valence Polyoxovanadate [GeV14O40]8–

As part of the search for systems in which control of quantum entanglement can be achieved, here we consider the paramagnetic mixed valence polyoxometalate K2Na6[GeV14O40]·10H2O in which two electrons are delocalized over the 14 vanadium ions. Applying a homogeneous electric field can induce an antiferromagnetic coupling between the two delocalized electronic spins that behave independently in the absence of the field. On the basis of the proposed theoretical model, we show that the external field can be used to generate controllable quantum entanglement between the two electronic spins traveling over a vanadium network of mixed valence polyoxoanion [GeV14O40]8–. Within a simplified two-lev…

Spin crossover FeII complexes as templates for bimetallic oxalate-based 3D magnets

Abstract We present the synthesis and structural characterization of the salt [Fe(bpp)2][MnCr(ox)3]2 · bpp · CH3OH. It crystallizes in the monoclinic space group. This material contains an anionic [MnCr(ox)3]− 3D 10-gon ferromagnetic network, that orders below 3.0 K. The channels created by this architecture are filled by the spin crossover cations [Fe(bpp)2]2+ (bpp = 2,6(bispyrazol-3-yl)pyridine), free ligand and solvent molecules. No spin transition has been observed at ambient pressure.

A Highly Sensitive Hybrid Colorimetric and Fluorometric Molecular Probe for Cyanide Sensing Based on a Subphthalocyanine Dye

A highly sensitive, selective colorimetric and fluorometric molecular probe based on a subphthalocyanine dye has been developed for cyanide-anion determination in aqueous solution. It has also been shown that a carboxysubphthalocyanine derivative can be covalently anchored to transparent mesoporous nanocrystalline high-surface-area metal oxide films to detect low concentrations of cyanide anion in pure water with no interference from other anionic or cationic species.

Orbitally dependent kinetic exchange in cobalt(II) pairs: origin of the magnetic anisotropy

Abstract A comprehensive theoretical study of the magnetic exchange between Co 2+ ions is reported. Using the microscopic background we deduce the general Hamiltonian for a corner-shared bioctahedral system involving kinetic exchange, spin–orbit coupling and low-symmetry local crystal field. This Hamiltonian acting within orbitally degenerate ground manifold 4 ( T 1g ) A ⊗ 4 ( T 1g ) B of the cobalt pair is expressed in terms of orbital and spin operators. We elucidate the major electronic factors controlling the exchange anisotropy in the Co(II) pairs. The degree of the magnetic anisotropy is shown to depend on the strength of the cubic crystal field and on the relative efficiency of two k…

Polymetallic oxalate-based 2D magnets: Soluble molecular precursors for the nanostructuration of magnetic oxides

Here we describe the synthesis and magnetic characterization of a family of 2D polymetallic oxalate-bridged polymeric networks with general formula [M(II)(H(2)O)(2)](3)[M(III)(ox)(3)](2)(18-crown-6)(2) (M(III) = Cr, Fe; M(II) = Mn, Fe, Co, Ni; 18-crown-6 = C(12)H(24)O(6)). Depending on the nature of the trivalent metal ion, they exhibit ferro- (Cr(3+)) or ferrimagnetic (Fe(3+)) ordering in the 3.6-20 K interval. In contrast with most of the oxalate-bridged CPs reported so far, these complexes do not need any additional templating cation for their assembly and represent the first series of oxalate-based polymeric networks which can be considered intrinsically neutral. As previously observed …

Molecule-Based Magnets Formed by Bimetallic Three-Dimensional Oxalate Networks and Chiral Tris(bipyridyl) Complex Cations. The Series [ZII(bpy)3][ClO4][MIICrIII(ox)3] (ZII = Ru, Fe, Co, and Ni; MII = Mn, Fe, Co, Ni, Cu, and Zn; ox = Oxalate Dianion)

The synthesis, structure, and physical properties of the series of molecular magnets formulated as [ZII(bpy)3][ClO4][MIICrIII(ox)3] (ZII = Ru, Fe, Co, and Ni; MII = Mn, Fe, Co, Ni, Cu, and Zn; ox = oxalate dianion) are presented. All the compounds are isostructural to the [Ru(bpy)3][ClO4][MnCr(ox)3] member whose structure (cubic space group P4(1)32 with a = 15.506(2) A, Z = 4) consists of a three-dimensional bimetallic network formed by alternating MII and CrIII ions connected by oxalate anions. The identical chirality (lambda in the solved crystal) of all the metallic centers determines the 3D chiral structure adopted by these compounds. The anionic 3D sublattice leaves some holes where th…

A New Conducting Molecular Solid Based on the Magnetic [Ni(dmf)6]2+ Cation and on [Ni(dsit)2]22− (dsit=1,3-dithiole-2-thione-4,5-diselenolate) Showing an Unprecedented Anion Packing

The synthesis, X-ray structure, magnetic and transport properties of the compound Ni(dmf) 6 [Ni(dsit) 2 ] 2 (dmf=dimethylformamide, dsit = 1,3-dithiole-2-thione-4,5-diselenolate) are described. This compound crystallizes in the monoclinic space group P2 1 /c, with a = 18.709(6), b = 22.975(5), c = 20.418(5) A, β = 99.31(2)° and Z = 6; its structure consists of [Ni(dsit) 2 ] 2- 2 dimers and isolated [Ni(dmf) 6 ] 2+ cations both centrosymmetric and non-centrosymmetric. The dimers are packed forming chains along the [101] direction with short Se...Se interdimer contacts. Additional interchains S...S contacts render this structure a three-dimensional character, never observed so far in other [N…

Electrostatic Anchoring of Mn4 Single-Molecule Magnets onto Chemically Modified Multiwalled Carbon Nanotubes

Two different routes that enable the electrostatic grafting of cationic single-molecule magnets (SMMs) onto the surface of chemically modified anionic multi-walled carbon nanotubes (MWNTs) are described. The chemical nature and physical properties of the resulting hybrids are discussed on the basis of a complete battery of experimental techniques. The data show that the chemical nature of the SMM unit remains intact, while its magnetic response is significantly affected by the grafting process, which is likely due to surface effects.

Out-of-plane transport of 1T-TaS2/graphene-based van der Waals heterostructures

Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the in-plane and out-of-plane entanglement in strongly correlated systems. A relevant example is provided by 1T-TaS2, which exhibits a multifaceted electronic and magnetic scenario due to the existence of several charge density wave (CDW) configurations. It includes quantum hidden phases, superconductivity and exotic quantum spin liquid (QSL) states, which are highly dependent on the out-of-plane stacking of the CDW. In this system, the interlayer stacking of the CDW is crucial for the interpretation of the underlying electronic and magnetic phase diagram. Here, thin-layers of 1T-TaS2 are …

Lanthanoid single-ion magnets based on polyoxometalates with a 5-fold symmetry: The series [LnP5W30O110]12– (Ln3+ = Tb, Dy, Ho, Er, Tm, and Yb)

A robust, stable and processable family of mononuclear lanthanoid complexes based on polyoxometalates (POMs) that exhibit single-molecule magnetic behavior is described here. Preyssler polyanions of general formula [LnP 5W 30O 110] 12- (Ln 3+ = Tb, Dy, Ho, Er, Tm, and Yb) have been characterized with static and dynamic magnetic measurements and heat capacity experiments. For the Dy and Ho derivatives, slow relaxation of the magnetization has been found. A simple interpretation of these properties is achieved by using crystal field theory. © 2012 American Chemical Society.

The EDTA Family of Molecular Based Ferromagnets

The bimetallic compounds of the EDTA family offer a large variety of ferrimagnetic model systems in which the dimensionality as well as the exchange-anisotropy can be controlled with ease. This paper deals with the magneto-structural chemistry of this kind of materials, paying particular attention to both the low-dimensional magnetic behavior and the three-dimcnsional magnetic ordering.

Attosecond soft-X-ray spectroscopy of a transition metal dichalcogenide material

We use attosecond soft X-ray pulses between 284 eV to 543 eV for orbital-selective and real-time probing of the opto-electronic response of semi metallic TiS2.

Mixed‐valence trinuclear manganese clusters : Influence of the electronic transfer on the magnetic properties

The magnetic behavior of mixed‐valence trinuclear clusters d4‐d4‐d5 is discussed on the basis of a model which takes into account valence delocalization and Heisenberg exchange. This model considers the competing effect between the electronic transfer and the localization of the extra electron due to an asymmetry of the triangular entity. The magnetic properties of the mixed‐valence oxo‐centered Mn(II)‐Mn(III)‐Mn(III) complexes formulated as Mn3O(O2CR)6L3 (R=Me, L=pyridine) are discussed on the basis of the developed model, supporting a significant intramolecular electron transfer. A comparison of these results to those previously reported by assuming a valence‐trapped model is given. Carlo…

Molecular magnetism: from chemical design to spin control in molecules, materials and devices

The field of molecular magnetism is rapidly evolving towards the use of magnetic molecules and molecule-based magnetic materials in physics-driven and nanotechnology-driven fields, in particular molecular spintronics, quantum technologies, metal–organic frameworks (MOFs) and 2D materials. In molecular spintronics, the goal is the development of a new generation of spintronic devices based on molecular materials or, in the longer term, on one or a few molecules. In the area of quantum technologies, the milestones reached in the design of molecular spin qubits with long quantum coherence times and in the implementation of quantum operations have raised expectations for the use of molecular sp…

Future directions in solid state chemistry: report of the NSF-sponsored workshop

Abstract A long-established area of scientific excellence in Europe, solid state chemistry has emerged in the US in the past two decades as a field experiencing rapid growth and development. At its core, it is an interdisciplinary melding of chemistry, physics, engineering, and materials science, as it focuses on the design, synthesis and structural characterization of new chemical compounds and characterization of their physical properties. As a consequence of this inherently interdisciplinary character, the solid state chemistry community is highly open to the influx of new ideas and directions. The inclusionary character of the field’s culture has been a significant factor in its continu…

ChemInform Abstract: Lanthanoid Single-Ion Magnets Based on Polyoxometalates with a 5-Fold Symmetry: The Series [LnP5W30O110]12-(Ln3+: Tb, Dy, Ho, Er, Tm, and Yb).

The compounds K12LnP5W30O110 ·nH2O (Ln3+: Tb, Dy, Ho, Er, Tm, and Yb) are prepared from aqueous solutions of K12.5Na1.5 [NaP5W30O110] and LnCl3 (autoclave, 160 °C, 24 h) and characterized by static and dynamic magnetic measurements.

Unravelling the chemical design of spin-crossover nanoparticles based on iron(ii)–triazole coordination polymers: towards a control of the spin transition

A systematic study of the key synthetic parameters that control the growth of spin-crossover (SCO) nanoparticles (NPs) using the reverse micelle technique has been undertaken in the system [Fe(Htrz)2(trz)](BF4)·H2O, (Htrz = 1,2,4-triazole). This has permitted us to modulate the physical properties of the NPs in a controlled and reproducible manner. In particular, a control over the size of the NPs (in the range 4 to 16 nm) has been achieved by varying the water to surfactant molar ratio. The consequences of this size variation on the cooperativity of the spin transition are discussed. Finally, this approach has been extended to the chemical alloy [Fe(Htrz)2.95(NH2trz)0.05](ClO4)2 in order t…

Stimuli responsive hybrid magnets : tuning the photoinduced spin-crossover in Fe(III) complexes inserted into layered magnets

The insertion of a [Fe(sal_2 trien)]^+ complex cation into a 2D oxalate network in the presence of different solvents results in a family of hybrid magnets with coexistence of magnetic ordering and photoinduced spin crossover (LIESST effect) in compounds [Fe^{III}(sal_2 trien)][Mn^{II}Cr^{III}(ox)_3]·CHCl_3 (1·CHCl_{3}) [Fe^{III}(sal_{2} trien)][Mn^{II}Cr^{III}(ox)_{3}]·CHBr_{3} (1·CHBr_{3}) and [Fe^{III}(sal_{2} trien)][Mn^{II}Cr^{III}(ox)_{3}]·CH_{2}Br_{2} (1·CH_{2}Br_{2}). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn^{II} and Cr^{III} ions linked through oxalate ligands and a layer of [Fe(sal_{2} trien)]^{+} complexes and solvent molecules (CHCl_{3} CHBr_{…

The ferrimagnetic compounds CoM[M’(EDTA)]2⋅4H2O(M,M’=Co,Ni): Magnetic characterization of CoCo[Ni(EDTA)2]⋅4H2O

Under the terms of the Creative Commons Attribution (CC BY) license to their work.

Magnetic Excitations in Tetrameric Clusters of Polyoxometalates Observed by Inelastic Neutron Scattering. Evidence for Anisotropic Exchange Interactions in Cobalt(II) Clusters.

Magnetic excitations in tetranuclear clusters of exchange-coupled metal ions encapsulated by polyoxotungstate ligands (1) have been observed by inelastic neutron scattering (INS) in the salts K10[M4(H2O)2(PW9O34)2]·nH2O, where M2+ = Mn, Co, and Ni. INS provides a much deeper and more detailed insight into the nature of the magnetic coupling in these clusters than bulk techniques. In particular, anisotropic exchange interactions are evidenced in the ferromagnetic Co4 cluster.

A Mixed-Ligand Approach for Spin-Crossover Modulation in a Linear FeII Coordination Polymer

In this work, we present a family of Fe(II) coordination polymers of general formula [Fe(btzx)(3-3x)(btix)(3x)](ClO4)2 with interesting spin-crossover properties. These coordination polymers have been synthesized using chemical mixtures of two different but closely related ligands, 1,4-bis(tetrazol-1-ylmethyl)benzene (btzx) and 1,4-bis(triazol-1-ylmethyl)benzene (btix), and the effect of a gradual substitution of the ligand in the spin transition temperature has been investigated. Several chemical mixtures have been structurally characterized by X-ray powder diffraction indicating a clear critical amount in the composition of the mixture after which mixed phases rather than a single phase c…

Spin-Crossover Modification through Selective CO2 Sorption

[EN] We present a spin-crossover Fe-II coordination polymer with no permanent channels that selectively sorbs CO2 over N-2. The one-dimensional chains display internal voids of similar to 9 angstrom diameter, each being capable to accept one molecule of CO2 at 1 bar and 273 K. X-ray diffraction provides direct structural evidence of the location of the gas molecules and reveals the formation of O=C=O(delta(-))center dot center dot center dot pi interactions. This physisorption modifies the spin transition, producing a 9 K increase in T-1/2.

Molecular vs. inorganic spintronics: The role of molecular materials and single molecules

Molecular spintronics is a new and emerging sub-area of spintronics that can benefit from the achievements obtained in molecular electronics and molecular magnetism. The two major trends of this area are the design of molecular analogs of the inorganic spintronic structures, and the evolution towards single-molecule spintronics. The former trend opens the possibility to design cheaper spintronic devices compatible with plastic technology, while the second takes advantage of the possibility to tailor molecules with control down to the single spin. In this highlight these two trends will be compared with the state-of-the-art achieved in the conventional inorganic spintronic systems.

Patterning of Magnetic Bimetallic Coordination Nanoparticles of Prussian Blue Derivatives by the Langmuir–Blodgett Technique

We report a novel method to prepare patterns of nanoparticles over large areas of the substrate. This method is based on the adsorption of the negatively charged nanoparticles dispersed in an aqueous subphase onto a monolayer of the phospholipid dipalmitoyl-l-α-phosphatidylcholine (DPPC) at the air-water interface. It has been used to prepare patterns of nanoparticles of Prussian blue analogues (PBA) of different size (K(0.25)Ni[Fe(CN)(6)](0.75) (NiFe), K(0.25)Ni[Cr(CN)(6)](0.75) (NiCr), K(0.25)Ni[Co(CN)(6)](0.75) (NiCo), Cs(0.4)Co[Cr(CN)(6)](0.8) (CsCoCr), and Cs(0.4)Co[Fe(CN)(6)](0.9) (CsCoFe)). The behavior of DPPC monolayer at the air-water interface in the presence of the subphase of P…

Iron(II) Complexes of 2,6-Di[4-(ethylcarboxy)pyrazol-1-yl]pyridine with Reversible Guest-Modulated Spin-Crossover Behavior

Tres solvatomorfos del complejo de hierro(II) de 2,6-di[4-(etilcarboxi)pirazol-1-il]piridina (bpCOOEt2p) de fórmulas [Fe(bpCOOEt2p)2](ClO4)2·1.5MeNO2 (1) , [Fe(bpCOOEt2p)2](ClO4)2·MeNO2 (2) y [Fe(bpCOOEt2p)2](ClO4)2·2MeNO2 (3) han sido preparados y caracterizados. Muestran interesantes propiedades de cruce de espín (SCO) que van desde transiciones de espín térmico parciales a completas y un efecto de captura de estado de espín excitado inducido por la luz (LIESST). En solvatomorph 2, se forma una estructura robusta con canales que permiten la entrada o eliminación de moléculas de solvente por difusión de vapor sin perder la cristalinidad. Por lo tanto, las muestras intercambiadas con disolv…

Sublimable chloroquinolinate lanthanoid single-ion magnets deposited on ferromagnetic electrodes† †Electronic supplementary information (ESI) available. CCDC 1557647–1557649. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc03463f

Magnetic analogues of Alq3 give rise to molecular/ferromagnetic interfaces with specific hybridization, opening the door to interesting spintronic effects.

CCDC 1045633: Experimental Crystal Structure Determination

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CCDC 2130642: Experimental Crystal Structure Determination

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CCDC 1473649: Experimental Crystal Structure Determination

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CCDC 1004948: Experimental Crystal Structure Determination

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CCDC 1491090: Experimental Crystal Structure Determination

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CCDC 1856807: Experimental Crystal Structure Determination

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CCDC 1427507: Experimental Crystal Structure Determination

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CCDC 2230343: Experimental Crystal Structure Determination

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CSD 2036360: Experimental Crystal Structure Determination

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CCDC 2059590: Experimental Crystal Structure Determination

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CCDC 982641: Experimental Crystal Structure Determination

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CSD 2024846: Experimental Crystal Structure Determination

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CCDC 1557895: Experimental Crystal Structure Determination

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CCDC 1920493: Experimental Crystal Structure Determination

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CCDC 1564530: Experimental Crystal Structure Determination

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CCDC 1446096: Experimental Crystal Structure Determination

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CCDC 1934948: Experimental Crystal Structure Determination

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CCDC 2059587: Experimental Crystal Structure Determination

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CCDC 1484963: Experimental Crystal Structure Determination

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CSD 1790045: Experimental Crystal Structure Determination

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CCDC 1457101: Experimental Crystal Structure Determination

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CCDC 955127: Experimental Crystal Structure Determination

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CCDC 2059591: Experimental Crystal Structure Determination

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CCDC 2230344: Experimental Crystal Structure Determination

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CCDC 1457100: Experimental Crystal Structure Determination

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CCDC 1562347: Experimental Crystal Structure Determination

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CCDC 1435056: Experimental Crystal Structure Determination

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CCDC 1564529: Experimental Crystal Structure Determination

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CCDC 953847: Experimental Crystal Structure Determination

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CCDC 1435057: Experimental Crystal Structure Determination

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CCDC 2059589: Experimental Crystal Structure Determination

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CCDC 929206: Experimental Crystal Structure Determination

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CCDC 910547: Experimental Crystal Structure Determination

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CCDC 1538254: Experimental Crystal Structure Determination

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CCDC 1421699: Experimental Crystal Structure Determination

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CCDC 1457102: Experimental Crystal Structure Determination

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CCDC 1473650: Experimental Crystal Structure Determination

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CCDC 1440481: Experimental Crystal Structure Determination

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CCDC 2230342: Experimental Crystal Structure Determination

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CCDC 955126: Experimental Crystal Structure Determination

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CCDC 1482838: Experimental Crystal Structure Determination

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CCDC 929201: Experimental Crystal Structure Determination

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CCDC 1856804: Experimental Crystal Structure Determination

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CCDC 2230348: Experimental Crystal Structure Determination

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CCDC 987661: Experimental Crystal Structure Determination

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CCDC 1582351: Experimental Crystal Structure Determination

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CCDC 1917753: Experimental Crystal Structure Determination

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CCDC 2230346: Experimental Crystal Structure Determination

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CCDC 1856814: Experimental Crystal Structure Determination

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CCDC 1440482: Experimental Crystal Structure Determination

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CCDC 1562346: Experimental Crystal Structure Determination

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CCDC 1446095: Experimental Crystal Structure Determination

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CCDC 1828115: Experimental Crystal Structure Determination

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CCDC 2209231: Experimental Crystal Structure Determination

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CCDC 1435058: Experimental Crystal Structure Determination

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CCDC 2209228: Experimental Crystal Structure Determination

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CCDC 1562348: Experimental Crystal Structure Determination

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CCDC 1435055: Experimental Crystal Structure Determination

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CCDC 1828114: Experimental Crystal Structure Determination

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CCDC 1482841: Experimental Crystal Structure Determination

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CCDC 1828117: Experimental Crystal Structure Determination

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CCDC 1003585: Experimental Crystal Structure Determination

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CCDC 2130640: Experimental Crystal Structure Determination

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CCDC 1439097: Experimental Crystal Structure Determination

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CCDC 904371: Experimental Crystal Structure Determination

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CCDC 987659: Experimental Crystal Structure Determination

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CCDC 929203: Experimental Crystal Structure Determination

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CCDC 1457103: Experimental Crystal Structure Determination

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CCDC 2068294: Experimental Crystal Structure Determination

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CCDC 1411200: Experimental Crystal Structure Determination

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CCDC 2209227: Experimental Crystal Structure Determination

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CSD 2036359: Experimental Crystal Structure Determination

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CCDC 910548: Experimental Crystal Structure Determination

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CCDC 927863: Experimental Crystal Structure Determination

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CCDC 1856808: Experimental Crystal Structure Determination

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CCDC 912971: Experimental Crystal Structure Determination

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CCDC 2213981: Experimental Crystal Structure Determination

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CCDC 998895: Experimental Crystal Structure Determination

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CCDC 2130639: Experimental Crystal Structure Determination

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CCDC 987658: Experimental Crystal Structure Determination

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CCDC 929204: Experimental Crystal Structure Determination

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CCDC 1856805: Experimental Crystal Structure Determination

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CCDC 1562344: Experimental Crystal Structure Determination

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CCDC 1054373: Experimental Crystal Structure Determination

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CCDC 998896: Experimental Crystal Structure Determination

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CCDC 1482842: Experimental Crystal Structure Determination

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CCDC 2230351: Experimental Crystal Structure Determination

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CCDC 1557648: Experimental Crystal Structure Determination

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CCDC 1557649: Experimental Crystal Structure Determination

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CCDC 1562345: Experimental Crystal Structure Determination

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CCDC 1934950: Experimental Crystal Structure Determination

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CCDC 1833302: Experimental Crystal Structure Determination

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CCDC 1562349: Experimental Crystal Structure Determination

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CCDC 1856813: Experimental Crystal Structure Determination

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CCDC 1054374: Experimental Crystal Structure Determination

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CCDC 973767: Experimental Crystal Structure Determination

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CCDC 1439096: Experimental Crystal Structure Determination

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CCDC 1045632: Experimental Crystal Structure Determination

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CCDC 1557896: Experimental Crystal Structure Determination

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CCDC 1538255: Experimental Crystal Structure Determination

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CCDC 1058520: Experimental Crystal Structure Determination

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CCDC 1045631: Experimental Crystal Structure Determination

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CCDC 1934947: Experimental Crystal Structure Determination

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CCDC 1917752: Experimental Crystal Structure Determination

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CCDC 1562351: Experimental Crystal Structure Determination

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CCDC 927864: Experimental Crystal Structure Determination

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CCDC 1856809: Experimental Crystal Structure Determination

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CCDC 2230349: Experimental Crystal Structure Determination

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CCDC 929205: Experimental Crystal Structure Determination

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CCDC 1828113: Experimental Crystal Structure Determination

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CCDC 1473651: Experimental Crystal Structure Determination

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CCDC 1934945: Experimental Crystal Structure Determination

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CCDC 2130641: Experimental Crystal Structure Determination

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CCDC 1446094: Experimental Crystal Structure Determination

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CCDC 1486674: Experimental Crystal Structure Determination

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CCDC 1435053: Experimental Crystal Structure Determination

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CCDC 977453: Experimental Crystal Structure Determination

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CCDC 1058519: Experimental Crystal Structure Determination

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CCDC 2213982: Experimental Crystal Structure Determination

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CCDC 1473652: Experimental Crystal Structure Determination

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CCDC 904370: Experimental Crystal Structure Determination

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CCDC 2230345: Experimental Crystal Structure Determination

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CCDC 987660: Experimental Crystal Structure Determination

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CCDC 953846: Experimental Crystal Structure Determination

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CCDC 1584808: Experimental Crystal Structure Determination

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CCDC 1856812: Experimental Crystal Structure Determination

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CCDC 927862: Experimental Crystal Structure Determination

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CSD 2036358: Experimental Crystal Structure Determination

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CCDC 1934949: Experimental Crystal Structure Determination

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CCDC 1491091: Experimental Crystal Structure Determination

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CCDC 1054616: Experimental Crystal Structure Determination

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CCDC 1446097: Experimental Crystal Structure Determination

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CCDC 2213983: Experimental Crystal Structure Determination

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CCDC 1420989: Experimental Crystal Structure Determination

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CCDC 2209230: Experimental Crystal Structure Determination

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CCDC 1562350: Experimental Crystal Structure Determination

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CCDC 1934946: Experimental Crystal Structure Determination

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CCDC 2209233: Experimental Crystal Structure Determination

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CCDC 1482839: Experimental Crystal Structure Determination

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CSD 2024847: Experimental Crystal Structure Determination

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CCDC 1856811: Experimental Crystal Structure Determination

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CCDC 912972: Experimental Crystal Structure Determination

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CCDC 1482840: Experimental Crystal Structure Determination

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CCDC 1457099: Experimental Crystal Structure Determination

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CCDC 984545: Experimental Crystal Structure Determination

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CCDC 2059588: Experimental Crystal Structure Determination

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CCDC 1446092: Experimental Crystal Structure Determination

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CCDC 987656: Experimental Crystal Structure Determination

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CCDC 1486675: Experimental Crystal Structure Determination

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CCDC 1435054: Experimental Crystal Structure Determination

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CCDC 1856810: Experimental Crystal Structure Determination

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CCDC 1917754: Experimental Crystal Structure Determination

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CCDC 2213984: Experimental Crystal Structure Determination

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CCDC 927865: Experimental Crystal Structure Determination

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CCDC 1856806: Experimental Crystal Structure Determination

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CCDC 987655: Experimental Crystal Structure Determination

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Quantum coherent spin-electric control in a molecular nanomagnet at clock transitions. Open data set

Data supporting the related publication.

CCDC 929202: Experimental Crystal Structure Determination

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CCDC 929207: Experimental Crystal Structure Determination

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CSD 1790044: Experimental Crystal Structure Determination

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CCDC 1427488: Experimental Crystal Structure Determination

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CCDC 1936956: Experimental Crystal Structure Determination

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CCDC 1484964: Experimental Crystal Structure Determination

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CCDC 2230347: Experimental Crystal Structure Determination

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CCDC 1473654: Experimental Crystal Structure Determination

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CCDC 929208: Experimental Crystal Structure Determination

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CCDC 940466: Experimental Crystal Structure Determination

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CCDC 953848: Experimental Crystal Structure Determination

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CCDC 973769: Experimental Crystal Structure Determination

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CCDC 2209232: Experimental Crystal Structure Determination

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CSD 2235856: Experimental Crystal Structure Determination

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CCDC 998898: Experimental Crystal Structure Determination

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CCDC 1917750: Experimental Crystal Structure Determination

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CCDC 2068293: Experimental Crystal Structure Determination

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CCDC 2230350: Experimental Crystal Structure Determination

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CCDC 953849: Experimental Crystal Structure Determination

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CCDC 2091526: Experimental Crystal Structure Determination

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CCDC 987657: Experimental Crystal Structure Determination

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CCDC 1538253: Experimental Crystal Structure Determination

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CCDC 987654: Experimental Crystal Structure Determination

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CCDC 1944600: Experimental Crystal Structure Determination

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CCDC 1917751: Experimental Crystal Structure Determination

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CCDC 1017983: Experimental Crystal Structure Determination

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CCDC 2068295: Experimental Crystal Structure Determination

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CCDC 1538256: Experimental Crystal Structure Determination

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CCDC 1944602: Experimental Crystal Structure Determination

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CCDC 1421701: Experimental Crystal Structure Determination

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CCDC 1473653: Experimental Crystal Structure Determination

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CCDC 912973: Experimental Crystal Structure Determination

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CCDC 2209229: Experimental Crystal Structure Determination

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Cover Feature: Boosting the Supercapacitive Behavior of CoAl Layered Double Hydroxides via Tuning the Metal Composition and Interlayer Space

The Cover Feature illustrates the improvement in the supercapacitive performance of CoAl layered double hydroxides (LDHs) after enlarging their interlayer space with anionic surfactants. This enhancement in the energy storage is ascribed to the increase in the electrochemical surface area (ECSA), the higher electrolyte diffusion, and the partial aluminum dissolution. PNICTOCHEM 804110 (G.A.) CIDEGENT/2018/001 Portada de revista, actividad de difusión.

Cover Picture. Energy Storage: Giant Enhancement in the Supercapacitance of NiFe-Graphene Nanocomposites Induced by a Magnetic Field (Adv. Mater. 28/2019)

The application of external magnetic fields to NiFe–graphene nanocomposites during the galvanostatic charge/discharge cycles induces a dramatic metal phase segregation, forming nanometric metal clusters of Ni with an outstanding electrochemical activity. This metal segregation leads to an enhancement in the capacitance of the nanocomposite, as described by Gonzalo Abellán, Eugenio Coronado, and co-workers in article number 1900189. PNICTOCHEM 804110 (G.A.) CIDEGENT/2018/001

Multistep spin switching in orthogonally-twisted ferromagnetic monolayers

The advent of twisting-engineering in two-dimensional (2D) crystals enables the design of van der Waals (vdW) heterostructures exhibiting emergent properties. In the case of magnets, this approach can afford artificial magnets with tailored spin arrangements that do not exist in nature. Here, we fabricate an artificial magnet by twisting 90 degrees two CrSBr ferromagnetic monolayers with an easy-axis in-plane anisotropy, thus forming an "orthogonally-twisted bilayer". The magneto-transport properties reveal multistep spin switching with a magnetic hysteresis opening, which is absent in the pristine case. By tuning the magnetic field, we modulate the remanent state and coercivity and select …