Search results for "Spin crossover"
showing 10 items of 379 documents
Interplay of Antiferromagnetic Coupling and Spin Crossover in Dinuclear Iron(II) Complexes
2003
This article reports on the study of the interplay between magnetic coupling and spin transition in 2,2′-bipyrimidine (bpym)-bridged iron(II) dinuclear compounds. Coexistence of both phenomena has been observed in [Fe(bpym)(NCS)2]2bpym, [Fe(bpym)(NCSe)2]2bpym and [Fe(bt)(NCS)2]2bpym (bpym = 2,2′-bipyrimidine, bt = 2,2′-bithiazoline) by the action of external physical factors namely pressure or electromagnetic radiation. Competition between magnetic exchange and spin crossover has been studied in [Fe(bpym)(NCS)2]2bpym at 6.3 kbar. LIESST experiments carried out in [Fe(bpym)(NCSe)2]2bpym and [Fe(bt)(NCS)2]2bpym at 4.2 K have shown that is possible to achieve dinuclear molecules with different…
Mixed spin-state [HS-LS] pairs in a dinuclear spin-transition complex: confirmation by variable-temperature 57Fe Mössbauer spectroscopy.
2008
Exquisite sensitivity of Mossbauer spectroscopy for tiny local molecular distortion is demonstrated in [FeII2(pmat)2](BF4)4?DMF: high-spin (HS) iron(II) in [HS-HS] and in [LS-HS] (low-spin–high-spin) pairs is clearly distinguished (see picture) for the first time without the need to apply a magnetic field. This dinuclear complex clearly shows that spin crossover via a [LS-HS] species is promoted by the use of a highly constrained bridging ligand (the bis-terdentate pmat).
X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2
2001
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) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2(mtz = methyltetrazole) (space groupP21/n) were measured between 300 and 10 K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78 K, the other site (B) remains in the LS state. Using the green lig…
Spin Transitions in Iron(II) Complexes
1996
Iron(II) has the 3d6 outer electronic configuration and hence its octahedral complexes may be either high-spin or low-spin. The high-spin configuration, t 2g 4 e g 2 , is adopted when relatively weak-field ligands are coordinated while the low-spin, t 2g 6 e g 0 , is obtained when strong-field ligands are involved. In Oh symmetry the ground states are 5T2g and lA1g, for the high-spin and low-spin configurations, respectively. While in most iron(II) six-coordinate complexes the symmetry is lower than Oh, these designations are generally adopted in the following sections for convenience. [Fe(H2O)6]2+ and [Fe(en)3]2+ (en = ethylenediamine) are typical examples of high-spin complexes, while [Fe…
Mixed-Valence, Mixed-Spin-State, and Heterometallic [2×2] Grid-type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Fe…
2005
Une famille de complexes heterometalliques [M 1 2 M 2 2 (L - ) 4 ] n + du type grille [2×2] 1-9 a ete preparee. Les trois approches synthetiques multietapes des ligands hydrazone heteroditopiques A-C possedent chacune des caracteristiques regio-, redox-, enantio-selectives. Ces ligands possedent un groupement NH ionisable et un groupement hydrazone non-ionisable NMe, qui permettent un controle des proprietes redox du metal complexe en fonction de la charge de la cavite coordinante. Les substituants 2-pyrimidine (R) et 6-pyridine (R') influencent de maniere significative la geometrie des complexes formes ainsi que leurs proprietes electrochimiques et magnetiques. Les etudes par spectroscopie…
New polynuclear 4,4ˈ-bis-1,2,4-triazole Fe(II) spin crossover compounds
2001
L'interet porte aux materiaux moleculaires du Fe(II) presentant une transition entre un etat haut-spin (HS, S = 2) et un etat bas-spin (LS, S = 0), sous l'effet d'une variation de temperature, de pression ou d'une irradiation lumineuse, n'a cesse de croitre au cours de ces dix dernieres annees [1-4]. La famille des composes du Fe(II) a base de derives du 1,2,4-triazole substitues par un groupe R sur l'azote 4 a ete tres etudiee pour ses proprietes de transition de spin (TS), qui pourraient permettre des applications en electronique moleculaire [5-15, 29, 32, 36, 37]. Nous avons recemment presente le premier compose a TS possedant une structure tridimensionnelle (figure 2). Ce compose de for…
Spin-Crossover and Liquid Crystal Properties in 2D Cyanide-Bridged FeII−MI/II Metalorganic Frameworks
2010
Novel two-dimensional heterometallic Fe(II)-M(Ni(II), Pd(II), Pt(II), Ag(I), and Au(I)) cyanide-bridged metalorganic frameworks exhibiting spin-crossover and liquid crystal properties, formulated as {FeL(2)[M(I/II)(CN)(x)](y)}·sH(2)O, where L are the ligands 4-(4-alkoxyphenyl)pyridine, 4-(3,4-dialkoxyphenyl)pyridine, and 4-(3,4,5-trisalkoxyphenyl)pyridine, have been synthesized and characterized. The physical characterization has been carried out by means of EXAFS, X-ray powder diffraction, magnetic susceptibility, differential scanning measurements, and Mössbauer spectroscopy. The 2D Fe(II) metallomesogens undergo incomplete and continuous thermally induced spin transition at T(1/2) ≈ 170 …
Thermal-,Pressure-, and Light-Induced Spin Transition in Novel Cyanide-Bridged FeII-AgI Bimetallic Compounds with Three-Dimensional Interpenetrating …
2002
[EN] Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds {Fe-II(pz)[Ag(CN)(2)](2)}.pz (pz= pyrazine), {Fe-II(4,4'-bipy)(2)[Ag(CN)(2)](2)} (4,4'-bipy-4,4'-bipyridine), and {Fe-II-(bpe)(2)[Ag(CN)(2)](2)} (bpe = bispyridylethylene), respectively. The single crystals of the bpe derivative undergo a spin transition with a large hysteresis loop at about 95 K. After several warming and cooling cycles, the single crystals become a microcrystalline powder with 50% spin transition. Influence of pressure- as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microc…
Photoinduced HS state in the first spin-crossover chain containing a cyanocarbanion as bridging ligand
2009
A new polymeric approach, based on cyanocarbanion ligands, for the design of spin crossover (SCO) compounds led us to the compound [Fe(abpt)2(tcpd)] (1) (tcpd^2 = (C[C(CN)2|3)^2 , abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) which has been characterised as the first SCO molecular chain involving a cyanocarbanion as bridging ligand. Gomez Garcia, Carlos Jose, Carlos.Gomez@uv.es
Iron(II) metallomesogens based on symmetrical tripod ligands
2012
Abstract Novel mononuclear tripodand-based iron(II) complexes showing liquid crystal properties have been synthesized and characterized. These are based on ligands tris[3-aza-4-((5-Cn)(6-R-2-pyridyl))but-3-enyl]amine, where R = hydrogen or methyl, 1,3,5-cis,cis-tris[1-aza-2-((5-alkyloxy)(2-pyridyl))vinyl]cyclohexane and 2,2,2-tris(2-aza-3-((5-alkyloxy)(2-pyridyl))prop-2-enyl)ethane. The physical characterization has been carried out by means of single-crystal X-ray diffraction measurements, magnetic susceptibility, differential scanning calorimetry, X-ray powder diffraction and Mossbauer spectroscopy.