Search results for "spin state"
showing 10 items of 254 documents
A thermal- and light-induced switchable one-dimensional rare loop-like spin crossover coordination polymer
2019
Rare loop-like isostructural one-dimensional coordination polymer (1D-CP) systems formulated as {Fe(DPIP)2(NCSe)2}n·4DMF (1) and {Fe(DPIP)2(NCSe)2}n·4DMF (2) were obtained by self-assembling FeII and pseudohalide NCX−(X = S, Se) ions in presence of the V-shaped bidentate bridging ligand, namely, N,N′-dipyridin-4-ylisophthalamide (DPIP), and were characterized by elemental analysis, IR spectroscopy, TGA, single crystal X-ray diffraction and powder X-ray diffraction. The magnetic studies show that complex 2 undergoes a complete thermally induced spin crossover (SCO) behavior centered at T1/2 = 120 K with ca. 5 K thermal hysteresis loop and light-induced excited spin state trapping effect (LIE…
An unprecedented hetero-bimetallic three-dimensional spin crossover coordination polymer based on the tetrahedral [Hg(SeCN)4]2− building block
2019
[EN] Self-assembly of octahedral FeII ions, trans-1,2-bis(4-pyridyl) ethane (bpe) bridging ligands and [Hg(XCN)(4)](2-) (X = S (1), Se (2)) tetrahedral building blocks has afforded a new type of hetero-bimetallic Hg-II-Fe-II spin-crossover (SCO) 3D 6,4-connected coordination polymer (CP) formulated {Fe(bpe)[Hg(XCN)(4)]}(n). For X = S (1), the ligand field is close to the crossing point but 1 remains paramagnetic over all temperatures. In contrast, for X = Se (2) the complex undergoes complete thermal induced SCO behaviour centred at T-1/2 = 107.8 K and complete photoconversion of the low spin state into a metastable high-spin state (LIESST effect) with T-LIESST = 66.7 K. The current results…
Thermal and optical switching of bistable iron compounds and possible applications
1993
Abstract Iron(II) coordination compounds with ligand field strengths close to the mean spin pairing energy may undergo thermal spin transition in the solid as well as in the liquid state. The thermodynamically stable state is high spin (HS) 5T2 (under Oh symmetry) with (t2)4 e2 electron configuration above the critical transition temperature Tc, and low spin (LS) 1A1 with (t2)6 electron configuration below Tc. The spin transition curve γHS(T) (molar fraction of HS molecules as function of temperature) can be abrupt or gradual, with or without hysteresis, or even with a plateau near Tc. Tc itself can vary over the whole temperature scale between the liquid helium region up to above room temp…
Metastable electronic states induced by nuclear decay and light
1994
Radioactive atoms incorporated in insulating solid-state compounds create various kinds of chemical and physical “after-effects” upon nuclear disintegration. Mossbauer emission spectroscopy of57Co-labelled coordination compounds has undoubtedly become the most informative technique to detect such after-effects like aliovalent charge and spin states of the nucleogenic iron atom resulting from the57Co(EC)57Fe decay, low energy excitations of crystal field and Zeeman states, linkage isomerism, radical formation with subsequent redox reactions, and others. We have extensively studied57Co-labelled complexes with [CoIIN6] cores employing time-integral and time-resolved Mossbauer emission spectros…
A Heteroleptic Push-Pull Substituted Iron(II) Bis(tridentate) Complex with Low-Energy Charge-Transfer States
2014
A heteroleptic iron(II) complex [Fe(dcpp)(ddpd)](2+) with a strongly electron-withdrawing ligand (dcpp, 2,6-bis(2-carboxypyridyl)pyridine) and a strongly electron-donating tridentate tripyridine ligand (ddpd, N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) is reported. Both ligands form six-membered chelate rings with the iron center, inducing a strong ligand field. This results in a high-energy, high-spin state ((5) T2 , (t2g )(4) (eg *)(2) ) and a low-spin ground state ((1) A1 , (t2g )(6) (eg *)(0) ). The intermediate triplet spin state ((3) T1 , (t2g )(5) (eg *)(1) ) is suggested to be between these states on the basis of the rapid dynamics after photoexcitation. The low-energy …
Control of the spin state by charge and ligand substitution: two-step spin crossover behaviour in a novel neutral iron(II) complex
2014
The influence of the charge and steric hindrance on the spin state of a series of four monomeric Fe-II complexes derived from the tridentate tigands 2-(1H-benzoimidazol-2-yl)-1,10-phenanthroline (Hphenbi) and 2-(1H-benzoimidazol-2-yl-9-methyl-1,10-phenanthroline (Hmphenbi) and their deprotonated forms (phenbi(-), mphenbi(-)) are investigated. The crystal structure and magnetic properties show that [Fe(Hphenbi)(2)](BF4)(2)center dot 1.5C(6)H(5)NO(2)center dot H2O (1) and its neutral form [Fe(phenbi)(2)]center dot 2CHCl(3)center dot H2O (2) are low-spin complexes at 400 K due to the strong ligand field imparted by the terpyridine-like tigand. In contrast, the steric hindrance induced by the m…
Spin switching in electronic devices based on 2D assemblies of spin-crossover nanoparticles
2015
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…
Spin state of a single-molecule magnet (SMM) creating long-range ordering on ferromagnetic layers of a magnetic tunnel junction – a Monte Carlo study
2021
Paramagnetic single-molecule magnets (SMMs) interacting with the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) produce a new system. The properties and future scope of new systems differ dramatically from the properties of isolated molecules and ferromagnets. However, it is unknown how far deep in the ferromagnetic electrode the impact of the paramagnetic molecule and ferromagnet interactions can travel for various levels of molecular spin states. Our prior experimental studies showed two types of paramagnetic SMMs, the hexanuclear Mn6 and octanuclear Fe–Ni molecular complexes, covalently bonded to ferromagnets produced unprecedented strong antiferromagnetic coupling between …
Unravelling the spin-state of solvated [Fe(bpp)2]2+ spin-crossover complexes: structure–function relationship
2018
This paper reports firstly the syntheses, crystal structures, and thermal and magnetic properties of spin crossover salts of formulae [Fe(bpp)2]3[Cr(CN)6]2·13H2O (1) and [Fe(bpp)2][N(CN)2]2·H2O (2) (bpp = 2,6-bis(pyrazol-3-yl)pyridine) exhibiting hydrogen-bonded networks of low-spin [Fe(bpp)2]2+ complexes and [Cr(CN)6]3− or [N(CN)2]− anions, with solvent molecules located in the voids. Desolvation of 1 is accompanied by a complete low-spin (LS) to a high-spin (HS) transformation that becomes reversible after rehydration by exposing the sample to the humidity of air. The influence of the lattice water on the magnetic properties of spin-crossover [Fe(bpp)2]X2 complex salts has been documented…
Nitrogen substitutional defects in silicon. A quantum mechanical investigation of the structural, electronic and vibrational properties
2019
RD and FSG acknowledges the CINECA award (HP10CTG8YY) under the ISCRA initiative, for the availability of high performance computing resources and support.