Search results for "osso"
showing 10 items of 801 documents
Does the solid-liquid crystal phase transition provoke the spin-state change in spin-crossover metallomesogens?
2008
Three types of interplay/synergy between spin-crossover (SCO) and liquid crystalline (LC) phase transitions can be predicted: (i) systems with coupled phase transitions, where the structural changes associated to the Cr LC phase transition drives the spin-state transition, (ii) systems where both transitions coexist in the same temperature region but are not coupled, and (iii) systems with uncoupled phase transitions. Here we present a new family of Fe(II) metallomesogens based on the ligand tris[3-aza-4-((5-C(n))(6-R)(2-pyridyl))but-3-enyl]amine, with C(n) = hexyloxy, dodecyloxy, hexadecyloxy, octadecyloxy, eicosyloxy, R = hydrogen or methyl (C(n)-trenH or C(n)-trenMe), which affords examp…
Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer
2017
[EN] Competition between spin-crossover and structural ligand ordering is identified as responsible for multistability and generation of six different phases in a rigid two-dimensional coordination polymer formulated {Fe-II[Hg-II(SCN)(3)](2) mu-(4,4'-bipy)(2)}(n) (1) (4,4'-bipy = 4,4'-bipyridine). The structure of 1 consists of infinite linear [Fe(mu-4,4'-bipy)](n)(2n+) chains linked by in situ formed {[Hg-II(SCN)(3)](2)(mu-4,4'-bipy)}(2n-) anionic dimers. The thermal dependence of the high-spin fraction, his, features four magnetic phases defined by steps following the sequence gamma(HS) = 1 (phase 1) gamma(HS) = 1/2 (phase 2) gamma(HS) approximate to 1/3 (phase 3) gamma(HS) = 0 (phase 4) …
Thermal and pressure-induced spin crossover in a novel three-dimensional Hoffman-like clathrate complex
2011
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 …
Correlations of the distribution of spin states in spin crossover compounds
1999
Abstract Short range correlations of the distribution of high spin (HS) and low spin (LS) states show up in thermal spin transition curves, decay curves of the light induced metastable HS state (LIESST state), and in structural features during the spin transitions. Correlations are due to short range interactions between the spin crossover molecules. Short range interactions may compete with omnipresent long range interactions and give rise to interesting spin transition phenomena. In this paper, the effect of correlations on the thermal spin transition in the mixed crystal system [Fe x Zn 1− x (pic) 3 ]Cl 2 ·EtOH (pic=picolylamine) is discussed. In particular the step in the thermal transi…
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…