Search results for "Spin Crossover"
showing 10 items of 379 documents
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 cro…
2015
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…
Iron(ii) complexes of tris(2-pyridylmethyl)amine (TPMA) and neutral bidentate ligands showing thermal- and photo-induced spin crossover
2018
Three new mononuclear Fe(ii) complexes have been prepared and characterized by the combination of tetradentate tris(2-pyridylmethyl)amine (TPMA) with three neutral bidentate ligands, such as ethylenediamine (en), 1,2-diaminopropane (pn) and 2-picolylamine (2-pic), in compounds [FeII(TPMA)(en)](ClO4)2 (1), [FeII(TPMA)(2-pic)](ClO4)2 (2) and [FeII(TPMA)(pn)](ClO4)2 (3). Structural and magnetic characterization demonstrates that the three compounds present a complete SCO behavior. The absence of strong intermolecular interactions and solvent molecules leads to reversible and gradual spin transitions. The different ligands allow tuning T1/2 from 130 K (2) to 325 K (3). The compound with the low…
Spin-Crossover Modification through Selective CO2 Sorption
2013
[EN] We present a spin-crossover Fe-II coordination polymer with no permanent channels that selectively sorbs CO2 over N-2. The one-dimensional chains display internal voids of similar to 9 angstrom diameter, each being capable to accept one molecule of CO2 at 1 bar and 273 K. X-ray diffraction provides direct structural evidence of the location of the gas molecules and reveals the formation of O=C=O(delta(-))center dot center dot center dot pi interactions. This physisorption modifies the spin transition, producing a 9 K increase in T-1/2.
Single-Crystal X-Ray Diffraction Study of Pressure and Temperature-Induced Spin Trapping in a Bistable Iron(II) Hofmann Framework.
2020
High-pressure single-crystal X-ray diffraction has been used to trap both the low-spin (LS) and high-spin (HS) states of the iron(II) Hofmann spin crossover framework, [FeII (pdm)(H2 O)[Ag(CN)2 ]2 ⋅H2 O, under identical experimental conditions, allowing the structural changes arising from the spin-transition to be deconvoluted from previously reported thermal effects.
Anomalous pressure dependence of the Lamb-Mössbauerf-factor in the spin crossover system [Fe(2-pic-ND2)3]Cl2·EtOD
1987
The pressure dependence of the Lamb-Mossbauer factor of the spin crossover compound [Fe(2-pic-ND2)3]Cl2·EtOD(2-pic-ND2=2-picolylamine, deuterated at the−NH2 group) has been measured at pressures up to 1500 bar and at three temperatures (115.7, 146.7, 185.6 K) around the transition temperatureT t=135 K. The temperature dependence of the unit cell volume has been determined by X-ray diffraction. In the transition region (T=146.7 K), the pressure dependence of thef-factor shows an anomalous increase as compared to the dependence below and above the transition. The behaviour off(p, T), its anomaly and absolute value, can be consistently explained within a theoretical model which treats the comp…
X-ray study of the light-induced metastable state of a spin-crossover compound
2000
Iron(II) complexes exhibiting thermal spin crossover may be converted from the1A1low-spin (LS) state to the5T2high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST). The lifetime of the metastable LIESST state may be sufficiently long for X-ray diffraction study. The lattice parameters of a single crystal of [Fe(ptz)6](BF4)2(ptz = propyltetrazole) were measured between 300 and 10 K, while the crystal changed from the HS to the LS state near 135 K. Using the green light (514 nm) of an argon-ion laser, the crystal was quantitatively converted to the metastable LIESST state at 10 K; its lattice parameters were measured up to 50 K, at which poin…
The LIESST state of [Fe(pic)3]Cl2.EtOH – the superstructure under continuous irradiation
2005
The superstructure recently discovered in [Fe(pic)3]Cl2.EtOH at temperatures inside the step region of the high-spin–low-spin transition curve sheds new light on the anomalous transition behaviour in spin crossover compounds. The structure of the metastable LIESST state of [Fe(pic)3]Cl2.EtOH at 10 K has been measured. The decay has been followed by X-ray diffraction using a CCD camera in order to detect reflections of the superstructure building up during the decay. No signal above the noise of the CCD camera was observed, so that even diffuse scattering could not be detected. This finding is in agreement with correlation lengths of pair correlations of molecules in the HS and LS states bei…
First Example of Coexistence of Thermal Spin Transition and Liquid-Crystal Properties.
2001
The rodlike FeIII complex of an N-alkyloxysalicylidenyl-N'-ethyl-N-ethylenediamine ligand, shown as a computer model in the picture, is the first compound in which spin-crossover (SC) and liquid-crystalline (LC) properties coexist. This synergy should allow the magnetic and optical properties of SC compounds to be combined with the sensitivity of the LC state to electromagnetic fields.
Spin Crossover Systems
2015
Abstract This account constitutes a basic introduction to spin crossover phenomena that is mostly encountered for iron(II) coordination complexes. After briefly describing the occurrence of spin transition in liquid and solid states, the effects of pressure and light irradiation are discussed. Applications and recent trends of this expanding field are also presented.
Spin crossover behavior in a series of iron(III) alkoxide complexes.
2015
The synthesis, crystal structures, magnetic behavior, and electron paramagnetic resonance studies of five new FeIII spin crossover (SCO) complexes are reported. The [FeIIIN5O] coordination core is constituted of the pentadentate ligand bztpen (N5) and a series of alkoxide anions (ethoxide, propoxide, n-butoxide, isobutoxide, and ethylene glycoxide). The methoxide derivative previously reported by us is also reinvestigated. The six complexes crystallize in the orthorhombic Pbca space group and show similar molecular structures and crystal packing. The coordination octahedron is strongly distorted in both the high- and low-temperature structures. The structural changes upon spin conversion ar…