Search results for "osso"

Coexistence of spin-crossover and antiferromagnetic coupling phenomena in the novel dinuclear Fe(II) complex [Fe(dpa)(NCS)2]2bpym

2003

Abstract The iron(II) spin crossover dinuclear compound [Fe(dpa)(NCS) 2 ] 2 bpym where dpa = 2,2 ′ -dipyridylamine and bpym = 2,2 ′ -bipyrimidine has been synthesized and characterized. Variable-temperature magnetic susceptibility and 57 Fe Mossbauer spectroscopy data provide evidence for a rather complete and continuous S=2 ( HS )↔S=0 (LS) spin-crossover behavior taking place in the temperature range 400–50 K (T 1/2 =245 K ) without the presence of a plateau at 50% of conversion. The absence of such plateau, which is characteristic of all dinuclear compounds so far studied, is interpreted in terms of synergetic effect between intramolecular and intermolecular interactions.

Polymorphism and Pressure Driven Thermal Spin Crossover Phenomenon in [Fe(abpt)2(NCX)2] (X=S, and Se): Synthesis,Structure and Magnetic Properties

2002

The monomeric compounds [Fe(abpt 2(NCX)2(X = S (1), Se (2) and abpt = 4-amino- 3,5-bis(pyridin-2-yl)-1,2,4-triazole) have been synthesized and characterized. They crystallize in the monoclinic P21/n space group with a = 11.637(2) A, b = 9.8021(14) A, c = 12.9838(12) A, β = 101.126(14)°, and Z=2 for 1, and a= 11.601(2) A, b = 9.6666(14) A, c = 12.883(2) A, β = 101.449(10)°, and Z = 2 for 2. The unit cell contains a pair mononuclear [Fe(abpt)2(NCX)21 units related by a center of symmetry. Each iron atom, located at a molecular inversion center, is in a distorted octahedral environment. Four of the six nitrogen atoms coordinated to the Fe(II) ion belong to the pyridine-N(1) and triazole-N(2) r…

Cover Picture: Mixed Spin-State [HS-LS] Pairs in a Dinuclear Spin-Transition Complex: Confirmation by Variable-Temperature57Fe Mössbauer Spectroscopy…

2008

Selective Photoswitching of the Binuclear Spin Crossover Compound{[Fe(bt)(NCS)2]2(bpm)}into Two Distinct Macroscopic Phases

2005

The low-spin (LS-LS, $S=0$) diamagnetic form of the binuclear spin crossover complex ${[\mathrm{Fe}(\mathrm{bt})(\mathrm{NCS}{)}_{2}{]}_{2}(\mathrm{bpm})}$ was selectively photoconverted into two distinct macroscopic phases at different excitation wavelengths (1342 or 647.1 nm). These long-lived metastable phases have been identified, respectively, as the symmetry-broken paramagnetic form (HS-LS, $\mathrm{S}=2$) and the antiferromagnetically coupled (HS-HS, $S=0$) high-spin form of the compound. The selectivity may be explained by the strong coupling of the primary excited states to the paramagnetic state.

Structural phase transition to disorder low-temperature phase in [Fe(ptz)6](BF4)2 spin-crossover compounds.

2012

In the spin-crossover compound [Fe(ptz)6](BF4)2 (where ptz=1-n-propyltetrazole) six different phases are observed. When a single crystal is slowly cooled from high temperatures to those below 125 K, the reflections broaden into diffuse maxima and split into two maxima along the c* direction [Kusz, Gütlich & Spiering (2004). Top. Curr. Chem. 234, 129–153]. As both maxima are broad along the c* direction, the short-range order exists only along the c direction and in the ab plane the structure remains long-range ordered. In this disordered phase additional satellite reflections appear. Upon heating above 135 K, the diffuse maxima return to their previous shape and this process is complete…

Polymorphism and “reverse” spin transition in the spin crossover system [Co(4-terpyridone)2](CF3SO3)2·1H2O

2009

[EN] Compound [Co(4-terpyridone)(2)](CF3SO3)(2)center dot 1H(2)O, where 4-terpyridone is 2,6-bis(2-pyridyl)-4(1H)-pyridone, forms two polymorphs. Polymorph 1 displays a continuous spin conversion in the temperature region 300-120 K while polymorph 2 shows, on cooling, the onset of a continuous high-spin (HS) to low-spin (LS) conversion interrupted by an abrupt "reverse'' spin transition in the temperature region 217-203 K. The formed unstable HS intermediate phase (IP) undergoes a strong cooperative "normal'' spin transition characterised by a hysteresis loop 33 K wide. The structural data give support for a crystallographic phase transition, which takes place concomitantly with the "revers…

Contribution of X-Ray diffraction to the study of spin transitions in some iron (II) complexes

1991

Abstract A review of recent single crystal investigations under constraint of iron (II) spin crossover complexes is given. The systems covered are Fe L2 (NCS)2 complexes (L = Phen, Btz) and some analogous derivatives. Emphasis is laid on the correlations between structural changes associated with spin transitions and the experimentally determined characteristics of these transitions.

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…