Search results for "crossover"
showing 10 items of 658 documents
Thermal and light induced polymorphism in iron(II) spin crossover compounds.
2004
The spin crossover complexes {Fe[H2B(pz)2]2L} ([H2B(pz)2]2 = dihydrobis(pyrazolyl)borate, L = 2,2'-bipyridine (1), bipy and 1,10-phenanthroline, phen (2)) undergo both thermal and light induced spin crossover, but the structure of the low spin and light induced high spin states for 2 are different from that of the thermally induced high spin state and from those of 1. Real Cabezos, Jose Antonio, Jose.A.Real@uv.es
Thermal- and photoinduced spin-state switching in an unprecedented three-dimensional bimetallic coordination polymer.
2005
The compound {Fe(pmd)[Ag(CN)2][Ag2(CN)3]} (pmd=pyrimidine) was synthesized and characterized. Magnetic, calorimetric and single crystal visible spectroscopic studies demonstrate the occurrence of a two-step high-spin (HS) right arrow over left arrow low-spin (LS) transition. The critical temperatures are T(c1)=185 and T(c2)=148 K. Each step involves approximately 50 % of the iron centers, with the low-temperature step showing a hysteresis of 2.5 K. The enthalpy and entropy variations associated with the two steps are DeltaH(1)=3.6+/-0.4 kJ mol(-1) and DeltaS(1)=19.5+/-3 J K(-1) mol(-1); DeltaH(2)=4.8+/-0.4 kJ mol(-1) and DeltaS(2)=33.5+/-3 J K(-1) mol(-1). Photomagnetic and visible spectros…
A spin transition molecular material with a wide bistability domain.
2002
International audience; [Fe(hyptrz)3](4-chloro-3-nitrophenylsulfonate)22 H2O (1; hyptrz=4-(3-hydroxypropyl)-1,2,4-triazole) has been synthesized and its physical properties have been investigated by several physical techniques including magnetic susceptibility measurements, calorimetry, and Mössbauer, optical, and EXAFS spectroscopy. Compound 1 exhibits a spin transition below room temperature, together with a very wide thermal hysteresis of about 50 K. This represents the widest hysteresis loop ever observed for an FeII-1,2,4-triazole spin transition material. The cooperativity is discussed on the basis of temperature-dependent EXAFS studies and of the structural features of a CuII analogu…
Substituent effects on the spin equilibrium in iron(II) pyrazolylborate complexes
1995
Abstract Two new complexes of the iron(II) pyrazolylborate system, [Fe(HB(pz)(dmpz) 2 ) 2 ] and [Fe(HB(pz) 2 (dmpz)) 2 ] (pz = pyrazole, dmpz = 3,5-dimethylpyrazole), have been prepared and found to exhibit thermal spin crossover in toluene solutions by means of optical spectroscopy and magnetic susceptibility measurements. Comparison with the published magnetic behaviour of the complexes [Fe(HB(dmpz) 3 ) 2 ] and [Fe(HB(pz) 3 ) 2 ] shows that the high spin state is stabilized with an increasing number of methyl substituents.
Electronic Structure Modulation in an Exceptionally Stable Non-Heme Nitrosyl Iron(II) Spin-Crossover Complex
2016
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…
Synthesis, structure and magnetic characterization of [Fe(bpp)2][Cu(pds)2]2·solv (solv=CH3CN and CH3OH)
2008
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…
A Switchable Molecular Rotator: Neutron Spectroscopy Study on a Polymeric Spin-Crossover Compound
2012
A quasielastic neutron scattering and solid-state 2H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN) 4]} shows that the switching of the rotation of a molecular fragment-the pyrazine ligand-occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10 -13-10 -3 s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppres…
Understanding the reactivity of transition metal complexes involving multiple spin states
2003
International audience; In coordination chemistry, many reactions involve several electronic states, in particular states of different spin. This phenomenon of ‘Multiple-State Reactivity’ has been recognized for some time, both for gas-phase reactions of ‘bare’ metal ions, and for transition metal complexes in solution. Until recently, however, much of the discussion of these systems has remained qualitative, because standard computational methods do not allow the location of the critical points for these processes, the Minimum Energy Crossing Points (MECPs) between states of different spin. Increased computational resources and new algorithms now enable MECPs to be located for large, reali…
Mössbauer investigation of the photoexcited spin states and crystal structure analysis of the spin-crossover dinuclear complex [{Fe(bt)(NCS)(2)}(2)bp…
2006
The crystal structure of the complex [{Fe(bt)(NCS)(2)}(2)bpym] (1) (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine) has been solved at 293, 240, 175 and 30 K. At all four temperatures the crystal remains in the P space group with a=8.7601(17), b=9.450(2), c=12.089(3) A, alpha=72.77(2), beta=79.150(19), gamma=66.392(18) degrees , V=873.1(4) Angstrom(3) (data for 293 K structure). The structure consists of centrosymmetric dinuclear units in which each iron(II) atom is coordinated by two NCS(-) ions in the cis position and two nitrogen atoms of the bridging bpym ligand, with the remaining positions occupied by the peripheral bt ligand. The iron atom is in a severely distorted octahedral FeN(6) e…
Spin-crossover nanoparticles anchored on MoS2 layers for heterostructures with tunable strain driven by thermal or light-induced spin switching
2021
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…