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…

Guest Effect on Nanopatterned Spin-Crossover Thin Films

International audience; Nanopatterned thin films of the metal–organic framework {Fe(bpac)[Pt(CN)4]} (bpac=bis(4‐pyridyl)acetylene) are elaborated by the combination of a sequential assembly process and a lithographic method. Raman microspectroscopy is used to probe the temperature dependence of the spin state of the iron(II) ions in the films (40–90 nm in thickness), and reveals an incomplete but cooperative spin transition comparable to that of the bulk material. Adsorption/desorption of pyridine guest molecules is found to have a substantial influence on the spin‐crossover properties of the thin layers. This interplay between host–guest and spin‐crossover properties in thin films and nano…

Wavelength selective light-induced magnetic effects in the binuclear spin crossover compound{[Fe(bt)(NCS)2]2(bpym)}

Using Fourier transform infrared spectroscopy, x-ray diffraction, and magnetic susceptibility measurements under light irradiation, the selective light-induced excited spin state trapping (LIESST) and the reversible-LIESST effect have been evidenced and studied in depth in the binuclear spin crossover compound {[Fe(bt)(NCS)2]2bpym}. In this system, each magnetic site can switch from low spin (LS) to high spin (HS), so that three states exist, namely, the LS-LS, HS-LS, and HS-HS. All these techniques shine a new light on the high phototunability of this system. In addition to the direct photoswitching from the LS-LS to the HS-LS or to the HS-HS state, here we show that photoinduced switching…

Hard-X-ray-induced excited-spin-state trapping.

Inside Front Cover: A Combined Top-Down/Bottom-Up Approach for the Nanoscale Patterning of Spin-Crossover Coordination Polymers (Adv. Mater. 16/2007)

The background scanning electron microscopy image shows nanometric patterns of the 3D spin crossover coordination polymer Fe(pyrazine)[Pt(CN)4] (see schematic structure in the circle), which have been fabricated using a combination of lift-off and multilayer sequential assembly methods. These patterns, reported by Gabor Molnar, Azzedine Bousseksou, and co-workers on p. 2163, exhibit a bistability of their electronic states (1A1 ⇌ 5T2), and thus represent a novel platform for a wide array of potential applications.

Electronic Structure Modulation in an Exceptionally Stable Non-Heme Nitrosyl Iron(II) Spin-Crossover Complex

The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6)(2) (bztpen=N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethylenediamine) displays an S=1/2 S=3/2 spin crossover (SCO) behavior (T-1/2=370 K, Delta H= 12.48 kJmol(-1), Delta S=33 JK(-1) mol(-1)) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0 S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120-420 K affording a detailed picture of how the electronic distribution of the t(2g)-e(g) orbitals modulates the structure of the {FeNO}(7) bond, providing valuable magneto-structural and spectroscopic correlat…

Selective Photoswitching of the Binuclear Spin Crossover Compound{[Fe(bt)(NCS)2]2(bpm)}into Two Distinct Macroscopic Phases

The low-spin (LS-LS, $S=0$) diamagnetic form of the binuclear spin crossover complex ${[\mathrm{Fe}(\mathrm{bt})(\mathrm{NCS}{)}_{2}{]}_{2}(\mathrm{bpm})}$ was selectively photoconverted into two distinct macroscopic phases at different excitation wavelengths (1342 or 647.1 nm). These long-lived metastable phases have been identified, respectively, as the symmetry-broken paramagnetic form (HS-LS, $\mathrm{S}=2$) and the antiferromagnetically coupled (HS-HS, $S=0$) high-spin form of the compound. The selectivity may be explained by the strong coupling of the primary excited states to the paramagnetic state.

Thermal neutron capture cross sections of tellurium isotopes

New values for thermal neutron capture cross sections of the tellurium isotopes 122Te, 124Te, 125Te, 126Te, 128Te, and 130Te are reported. These values are based on a combination of newly determined partial g-ray cross sections obtained from experiments on targets contained natural Te and gamma intensities per capture of individual Te isotopes. Isomeric ratios for the thermal neutron capture on the even tellurium isotopes are also given.

Enhanced porosity in a new 3D Hofmann-like network exhibiting humidity sensitive cooperative spin transitions at room temperature

The porous coordination polymers (PCPs) of general formula {Fe(bpac)[M(CN)4]}·guest (M = Pt, Pd) exhibit larger channels than previously synthesised 3D-Hofmann-like PCP. The channels are partially occupied by uncoordinated guest bpac ligands and labile H2O molecules. These PCPs exhibit very scarce cooperative spin crossover behaviour around room temperature with a large hysteresis loop (up to 49 K) and also display sensitivity to humidity and guest molecules. The inclusion of bpac molecules in the 3D network can be avoided by adding competitive volatile molecules during the crystallization process, affording the guest-free material. The spin crossover behavior of different guest and guest-f…

Bidirectional photo-switching of the spin state of iron(II) ions in a triazol based spin crossover complex within the thermal hysteresis loop

Abstract We have investigated the effect of short laser pulses (532 nm, 4 ns, −2 ) on the spin state of iron(II) ions in the spin crossover compound {[Fe II (Htrz) 2 (trz)](BF 4 )} within the hysteresis region of the high-spin (HS) to low-spin (LS) first-order thermal phase transition. Using Raman spectroscopy we have evidenced quasi-complete HS → LS as well as LS → HS photo-conversions, which can be induced by a single laser shot in the descending (351 K) and ascending (378 K) branches of the hysteresis loop, respectively. No effect has been observed, however, close to the center of the hysteresis loop even for repeated exposures.

High quality nano-patterned thin films of the coordination compound {Fe(pyrazine)[Pt(CN)4]} deposited layer-by-layer

International audience; An optimised procedure was developed for the layer-by-layer deposition of the Hofmann clathrate-like coordination compound {Fe(pyrazine)[Pt(CN)4]} either as continuous or as nano-patterned thin films. Characterization of the thickness and topography of the thin films by atomic force microscopy (AFM) and by surface plasmon resonance (SPR) spectroscopy, which also yields the layer's refractive index and losses, are reported. We found that the films are of good optical quality and the results of both AFM and SPR experiments are in good agreement with the theoretical predictions of the films thicknesses.

[Fe(TPT)(2/3){M(I)(CN)2}2]⋅nSolv (M(I) = Ag, Au): new bimetallic porous coordination polymers with spin-crossover properties.

Two new heterobimetallic porous coordination polymers with the formula [Fe(TPT)2/3{MI(CN)2}2]¿nSolv (TPT=[(2,4,6-tris(4-pyridyl)-1,3,5-triazine]; MI=Ag (nSolv=0, 1¿MeOH, 2¿CH2Cl2), Au (nSolv=0, 2¿CH2Cl2)) have been synthesized and their crystal structures were determined at 120¿K and 293¿K by single-crystal X-ray analysis. These structures crystallized in the trigonal R-3m space group. The FeII ion resides at an inversion centre that defines a [FeN6] coordination core. Four dicyanometallate groups coordinate at the equatorial positions, whilst the axial positions are occupied by the TPT ligand. Each TPT ligand is centred in a ternary axis and bridges three crystallographically equivalent Fe…

Titelbild: One Shot Laser Pulse Induced Reversible Spin Transition in the Spin-Crossover Complex [Fe(C4H4N2){Pt(CN)4}] at Room Temperature (Angew. Chem. 26/2005)

Spin crossover and photomagnetism in dinuclear iron(II) compounds

Abstract In this paper, we review recent work reported in the field of molecular spin crossover phenomena in dinuclear compounds. Following a comprehensive overview on the synthesis and properties of new iron(II) dinuclear compounds presenting the spin crossover phenomenon, we focus this review on recent efforts made in studying and understanding the photo-physical properties of the {[Fe(L)(NCX)2]2bpym} (L = bt or bpym, X = S or Se) family of compounds. Finally, literature on the different theoretical approaches treating the static and dynamic properties of dinuclear complexes presenting two-step thermal spin transition is briefly summarized.

Cover Picture: One Shot Laser Pulse Induced Reversible Spin Transition in the Spin-Crossover Complex [Fe(C4H4N2){Pt(CN)4}] at Room Temperature (Angew. Chem. Int. Ed. 26/2005)

Spin Crossover Metal-Organic Frameworks with Inserted Photoactive Guests: On the Quest to Control the Spin State by Photoisomerization

International audience; Three Hofmann-like metal-organic frameworks {Fe(bpac)[Pt(CN)4]}•G (bpac=1,2-bis(4-pyridyl)acetylene) were synthesized with photoisomerizable guest molecules (G = trans-azobenzene, trans-stilbene or cis-stilbene) and were characterized by elemental analysis, thermogravimetry and powder X-ray diffraction. The insertion of guest molecules and their conformation were inferred from Raman and FTIR spectra and from single-crystal X-ray diffraction and confronted with computational simulation. The magnetic and photomagnetic behaviors of the framework are significantly altered by the different guest molecules and different conformations. On the other hand, photoisomerization …

Pressure effect investigations on spin-crossover coordination compounds

International audience; The piezochromic properties of spin-crossover complexes have been recognized for a long time, with increasing pressure favouring the low spin state due to its smaller volume and therefore shifting the spin equilibrium towards higher temperatures and accelerating the relaxation at a given temperature. However, the interpretation and quantification of pressure-induced changes have been several times compromised by the relatively poor and incomplete spectral and structural information provided by the detection methods or due to the experimental difficulties related to the need for hydrostatic conditions at low temperatures. The present review is therefore primarily focu…

Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

Abstract Thermal and pressure effects have been investigated on the [Fe(sal 2 -trien)][Ni(dmit) 2 ] spin crossover complex by means of Mossbauer spectroscopic, calorimetric, X-ray diffraction and magnetic susceptibility measurements. The complex displays a complete thermal spin transition between the S = 5 2 and S = 1 2 spin states of Fe III near 245 K with a hysteresis loop of ca. 30 K. This transition is characterised by a change of the enthalpy, Δ H HL =7 kJ/mol, entropy, Δ S HL =29 J/Kmol, and the unit cell volume, Δ V HL =15.4 A 3 . Under hydrostatic pressures up to 5.7 kbar the thermal transition shifts to higher temperatures by ca. 16 K/kbar. Interestingly, at a low applied pressure …

Tunable Spin-Crossover Behavior of the Hofmann-like Network {Fe(bpac)[Pt(CN) 4 ]} through Host-Guest Chemistry

A study of the spin-crossover (SCO) behavior of the tridimensional porous coordination polymer {Fe(bpac)[Pt(CN)4]} (bpac=bis(4-pyridyl) acetylene) on adsorption of different mono- and polyhalobenzene guest molecules is presented. The resolution of the crystal structure of {Fe(bpac)[Pt(CN) 4]}A?G (G=1,2,4-trichlorobenzene) shows preferential guest sites establishing I?A?A?A?I? stacking interactions with the host framework. These host-guest interactions may explain the relationship between the modification of the SCO behavior and both the chemical nature of the guest molecule (electronic factors) and the number of adsorbed molecules (steric factors). Copyright © 2013 WILEY-VCH Verlag GmbH & …

One Shot Laser Pulse Induced Reversible Spin Transition in the Spin-Crossover Complex [Fe(C4H4N2){Pt(CN)4}] at Room Temperature

Synergetic effect of host-guest chemistry and spin crossover in 3D Hofmann-like metal-organic frameworks [Fe(bpac)M(CN)4] (M=Pt, Pd, Ni).

The synthesis and characterization of a series of three-dimensional (3D) Hofmann-like clathrate porous metal-organic framework (MOF) materials [Fe(bpac)M(CN) 4] (M=Pt, Pd, and Ni; bpac=bis(4-pyridyl)acetylene) that exhibit spin-crossover behavior is reported. The rigid bpac ligand is longer than the previously used azopyridine and pyrazine and has been selected with the aim to improve both the spin-crossover properties and the porosity of the corresponding porous coordination polymers (PCPs). The 3D network is composed of successive {Fe[M(CN) 4]} n planar layers bridged by the bis-monodentate bpac ligand linked in the apical positions of the iron center. The large void between the layers, w…

Crystal structure, magnetic properties and Mössbauer studies of [Fe(qsal)2][Ni(dmit)2]

Abstract A new compound of formula [Fe(qsal)2][Ni(dmit)2] (1) has been synthesised, structurally and magnetically characterised (qsalH = N-(8-quinolyl)salicylaldimine, dmit2− = 1,3-dithiol-2-thione-4,5-dithiolato). Its structural features and its magnetic behaviour were compared with those of [Fe(qsal)2]-based complexes, and more particularly [Fe(qsal)2][Ni(dmit)2] · 2CH3CN.

Homoleptic iron(II) complexes with the ionogenic ligand 6,6′-Bis(1H-tetrazol-5-yl)-2,2′-bipyridine: spin crossover behavior in a singular 2D spin crossover coordination polymer

Deprotonation of the ionogenic tetradentate ligand 6,6′-bis(1H-tetrazol-5-yl)-2,2′-bipyridine [H2bipy(ttr)2] in the presence of FeII in solution has afforded an anionic mononuclear complex and a neutral two-dimensional coordination polymer formulated as, respectively, NEt3H{Fe[bipy(ttr)2][Hbipy(ttr)2]}·3MeOH (1) and {Fe[bipy(ttr)2]}n (2). The anions [Hbipy(ttr)2]− and [bipy(ttr)2]2– embrace the FeII centers defining discrete molecular units 1 with the FeII ion lying in a distorted bisdisphenoid dodecahedron, a rare example of octacoordination in the coordination environment of this cation. The magnetic behavior of 1 shows that the FeII is high-spin, and its Mössbauer spectrum is characteriz…

Thermal and pressure-induced spin crossover in a novel three-dimensional Hoffman-like clathrate complex

The synthesis and crystal structure of the interpenetrated metal–organic framework material Fe(bpac)2[Ag(CN)2]2 (bpac = 4,4′-bis(pyridyl)acetylene) are reported along with the characterization of its spin crossover properties by variable temperature magnetometry and Mossbauer spectroscopy. The complex presents an incomplete stepped spin transition as a function of temperature that is modified upon successive thermal cycling. The pressure-induced transition has also been investigated by means of high pressure Raman spectroscopy using a diamond anvil cell. The results show that it is possible to reach the thermally-inaccessible fully low spin state at room temperature by applying hydrostatic …

A Combined Top-Down/Bottom-Up Approach for the Nanoscale Patterning of Spin-Crossover Coordination Polymers

Molecular spin-crossover complexes of 3d–3d transitionmetal ions have been the focus of many researchers’ work because of their fascinating properties associated with the bistability of their electronic states (high spin (HS) or low spin (LS)). Although the origin of the spin-crossover phenomenon is purely molecular, the macroscopic behavior of these systems in the solid state is strongly determined by the interactions, of mainly elastic origin, between the transition-metal ions. Recently, remarkable progress has been made in the area of spin-crossover complexes with infinite one-, two-, or three-dimensional (1D, 2D, 3D) networks, the so-called coordination polymers. The purpose of this app…

Multilayer Sequential Assembly of Thin Films That Display Room-Temperature Spin Crossover with Hysteresis

Thermochromic Meltable Materials with Reverse Spin Transition Controlled by Chemical Design

International audience; We report a series of meltable FeII complexes, which, depending on the length of aliphatic chains, display abrupt forward low‐spin to high‐spin transition or unprecedented melting‐triggered reverse high‐spin to low‐spin transition on temperature rise. The reverse spin transition is perfectly reproducible on thermal cycling and the obtained materials are easily processable in the form of thin film owing to their soft‐matter nature. We found that the discovered approach represents a potentially generalizable new avenue to control both the location in temperature and the direction of the spin transition in meltable compounds.

Induktion langlebiger angeregter Spinzustände durch harte Röntgenstrahlung

Light induced excited spin state trapping in the binuclear spin crossover compound [Fe(bpym)(NCS)2]2(bpym) exhibiting a high-spin ground state

Abstract A photo-magnetic effect is evidenced using near-infrared light in the binuclear complex [Fe(bpym)(NCS) 2 ] 2 (bpym). This compound has a 5 T 2g – 5 T 2g ground state and exhibits no thermal spin crossover – in contrast to the analogous [Fe(bpym)(NCSe) 2 ] 2 (bpym). The estimated photo-conversion ratio is ca. 30%. By means of magnetic susceptibility measurements as well as Raman and infrared absorption spectroscopies, the nature of the photo-induced phase was established as the 5 T 2g – 1 A 1g state, which means that only one iron center is converted to low-spin. The photo-induced state was completely converted back to the ground state either by visible light excitation or by heatin…

CCDC 2042717: Experimental Crystal Structure Determination

Related Article: Barbora Brachňaková, Ján Moncoľ, Ján Pavlik, Ivan Šalitroš, Sébastien Bonhommeau, Francisco Javier Valverde-Muñoz, Lionel Salmon, Gábor Molnár, Lucie Routaboul, Azzedine Bousseksou|2021|Dalton Trans.|50|8877|doi:10.1039/D1DT01057C

CCDC 1418191: Experimental Crystal Structure Determination

Related Article: Maksym Seredyuk , Lucía Piñeiro-López , M. Carmen Muñoz , Francisco J. Martínez-Casado , Gábor Molnár , José Alberto Rodriguez-Velamazán , Azzedine Bousseksou , José Antonio Real|2015|Inorg.Chem.|54|7424|doi:10.1021/acs.inorgchem.5b01001

CCDC 1418192: Experimental Crystal Structure Determination

Related Article: Maksym Seredyuk , Lucía Piñeiro-López , M. Carmen Muñoz , Francisco J. Martínez-Casado , Gábor Molnár , José Alberto Rodriguez-Velamazán , Azzedine Bousseksou , José Antonio Real|2015|Inorg.Chem.|54|7424|doi:10.1021/acs.inorgchem.5b01001

CCDC 904082: Experimental Crystal Structure Determination

Related Article: Zulema Arcís-Castillo, M. Carmen Muñoz, Gábor Molnár, Azzedine Bousseksou, José Antonio Real|2013|Chem.-Eur.J.|19|6851|doi:10.1002/chem.201203559

CCDC 904083: Experimental Crystal Structure Determination

Related Article: Zulema Arcís-Castillo, M. Carmen Muñoz, Gábor Molnár, Azzedine Bousseksou, José Antonio Real|2013|Chem.-Eur.J.|19|6851|doi:10.1002/chem.201203559

CCDC 1994888: Experimental Crystal Structure Determination

Related Article: Francisco‐Javier Valverde‐Muñoz, Maksym Seredyuk, M. Carmen Muñoz, Gábor Molnár, Yurii S. Bibik, José Antonio Real|2020|Angew.Chem.,Int.Ed.|59|18632|doi:10.1002/anie.202006453

CCDC 1418190: Experimental Crystal Structure Determination

Related Article: Maksym Seredyuk , Lucía Piñeiro-López , M. Carmen Muñoz , Francisco J. Martínez-Casado , Gábor Molnár , José Alberto Rodriguez-Velamazán , Azzedine Bousseksou , José Antonio Real|2015|Inorg.Chem.|54|7424|doi:10.1021/acs.inorgchem.5b01001

CCDC 2042716: Experimental Crystal Structure Determination

Related Article: Barbora Brachňaková, Ján Moncoľ, Ján Pavlik, Ivan Šalitroš, Sébastien Bonhommeau, Francisco Javier Valverde-Muñoz, Lionel Salmon, Gábor Molnár, Lucie Routaboul, Azzedine Bousseksou|2021|Dalton Trans.|50|8877|doi:10.1039/D1DT01057C

CCDC 904080: Experimental Crystal Structure Determination

Related Article: Zulema Arcís-Castillo, M. Carmen Muñoz, Gábor Molnár, Azzedine Bousseksou, José Antonio Real|2013|Chem.-Eur.J.|19|6851|doi:10.1002/chem.201203559

CCDC 920626: Experimental Crystal Structure Determination

Related Article: Carlos Bartual-Murgui, Amal Akou, Helena J. Shepherd, Gábor Molnár, J. Antonio Real, Lionel Salmon, Azzedine Bousseksou|2013|Chem.-Eur.J.|19|15036|doi:10.1002/chem.201300227

CCDC 904081: Experimental Crystal Structure Determination

Related Article: Zulema Arcís-Castillo, M. Carmen Muñoz, Gábor Molnár, Azzedine Bousseksou, José Antonio Real|2013|Chem.-Eur.J.|19|6851|doi:10.1002/chem.201203559

CCDC 904079: Experimental Crystal Structure Determination

Related Article: Zulema Arcís-Castillo, M. Carmen Muñoz, Gábor Molnár, Azzedine Bousseksou, José Antonio Real|2013|Chem.-Eur.J.|19|6851|doi:10.1002/chem.201203559