Search results for "crossover"
showing 10 items of 658 documents
Guest induced reversible on–off switching of elastic frustration in a 3D spin crossover coordination polymer with room temperature hysteretic behavio…
2021
A binary reversible switch between low-temperature multi-step spin crossover (SCO), through the evolution of the population γHS(T) with high-spin (HS)-low-spin (LS) sequence: HS1LS0 (state 1) ↔ HS2/3LS1/3 (state 2) ↔ HS1/2LS1/2 (state 3) ↔ HS1/3LS2/3 (state 4) ↔ HS0LS1 (state 5), and complete one step hysteretic spin transition featuring 20 K wide thermal hysteresis centred at 290 K occurs in the three-dimensional (3D) Hofmann-type porous coordination polymer {FeII(3,8phen)[Au(CN)2]2}·xPhNO2 (3,8phen = 3,8-phenanthroline, PhNO2 = nitrobenzene), made up of two identical interpenetrated pcu-type frameworks. The included PhNO2 guest (x = 1, 1·PhNO2) acts as a molecular wedge between the interp…
Pressure effect investigations on spin-crossover coordination compounds
2018
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…
Solvent-induced high-spin transition in double-decker 3d–4f metallacrowns
2019
Element-specific magnetic spin and orbital magnetic moments of $3d\text{\ensuremath{-}}4f$ double-decker metallacrown molecules have been investigated using x-ray magnetic circular dichroism. The double-decker metallacrowns comprise one rare-earth Gd(III) or Tb(III) ion embedded between two squared scaffolds of four Ni(II) ions. We observe a strong increase of the Ni(II) moments if the molecules are dissolved in methanol, indicating a spin crossover from a low-spin to a high-spin state. In contrast, dichloromethane does not change the spin state. This result is explained by a change of the coordination environment of nickel. The comparison of charge-transfer multiplet calculations with the …
Spin Crossover Metal-Organic Frameworks with Inserted Photoactive Guests: On the Quest to Control the Spin State by Photoisomerization
2021
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 …
Guest Effect on Nanopatterned Spin-Crossover Thin Films
2011
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…
Molecular magnetism: from chemical design to spin control in molecules, materials and devices
2019
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…
Smart molecular/MoS2 Heterostructures Featuring Light and Thermally-Induced Strain Driven by Spin Switching
2020
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…
Bimetallic MnIII–FeII hybrid complexes formed by a functionalized MnIII Anderson polyoxometalate coordinated to FeII: observation of a field-induced …
2015
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…
Electroswitching of the single-molecule magnet behaviour in an octahedral spin crossover cobalt(ii) complex with a redox-active pyridinediimine ligand
2020
Thermal-assisted spin crossover and field-induced slow magnetic relaxation coexist in the solid state for the mononuclear cobalt(II) complex with the non-innocent 2,6-bis(N-4-methoxyphenylformimidoyl)pyridine ligand. One-electron oxidation of the paramagnetic low-spin CoII ion (SCo = 1/2) to the diamagnetic low-spin CoIII ion (SCo = 0) leads to the electroswitching of the slow magnetic relaxation in acetonitrile solution.
A genetic algorithm for the minimum generating set problem
2016
Graphical abstractDisplay Omitted HighlightsWe propose a novel formulation for the MGS problem based on multiple knapsack.The so-conceived MGS problem is solved by a novel GA.The GA embeds an intelligent construction method and specialized crossover operators.We perform a thorough comparison with regards to state-of-the-art algorithms.The proposal proves to be very competitive, specially for large and hard instances. Given a set of positive integers S, the minimum generating set problem consists in finding a set of positive integers T with a minimum cardinality such that every element of S can be expressed as the sum of a subset of elements in T. It constitutes a natural problem in combinat…