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Spin-crossover Compound (spin-crossover + compound)

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Chemistry	100%

Selected Abstracts

X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001
Joachim Kusz
Iron(II) complexes exhibiting thermal spin-crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-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 group P21/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 light (514,nm) of an argon ion laser the crystal was quantitatively converted to the HS state at 10,K. Irradiation of the crystal at 10,K by red light of a laser diode (820,nm) with site A in the LS and site B in the HS state converts site B almost completely to the LS state. The lattice parameters of both metastable states were measured up to 50,K, where they start to decay on a minute timescale. At 10,K, a full data set for evaluation of the crystal structure was recorded. The volume change of the crystal per complex molecule accompanying the spin transition is 31.5,Å3 at site A and close to zero [,0.21,(14),Å3] at site B. [source]

X-ray study of the light-induced metastable state of a spin-crossover compound

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2000
Joachim Kusz
Iron(II) complexes exhibiting thermal spin crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-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 point the LIESST state begins to decay on a minute timescale. The change of the lattice parameters can be interpreted by a superposition of a normal temperature dependence, for which the isostructural zinc compound served as a reference, and an almost temperature-independent part which is proportional to the fraction of molecules in the HS state. [source]

Structural and Magnetic Resolution of a Two-Step Full Spin-Crossover Transition in a Dinuclear Iron(II) Pyridyl-Bridged Compound

CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2006
Jarrod J. M. Amoore
Abstract A dinuclear iron(II) complex containing the new pyridyl bridging ligand, 2,5-di(2,,2,,-dipyridylamino)pyridine (ddpp) has been synthesised and characterised by single-crystal X-ray diffraction, magnetic susceptibility and Mössbauer spectral methods. This compound, [Fe2(ddpp)2(NCS)4],4,CH2Cl2, undergoes a two-step full spin crossover. Structural analysis at each of the three plateau temperatures has revealed a dinuclear molecule with spin states HS,HS, HS,LS and LS,LS (HS: high spin, LS: low spin) for the two iron(II) centres. This is the first time that resolution of the metal centres in a HS,LS ordered state has been achieved in a two-step dinuclear iron(II) spin-crossover compound. Thermogravimetric data show that the dichloromethane solvate molecules can be removed in two distinct steps at 120,°C and 200,°C. The partially de-solvated clathrate, [Fe2(ddpp)2(NCS)4],CH2Cl2, undergoes a one-step transition with an increased transition temperature with respect to the as synthesised material. Structural characterisation of this material reveals subtle changes to the coordination geometries at each of the iron(II) centres and striking changes to the local environment of the dinuclear complex. The fully de-solvated material remains high spin over all temperatures. Interestingly, the solvent can be re-introduced into the monosolvated solid to achieve complete conversion back to the original two-step crossover material, [Fe2(ddpp)2(NCS)4],4,CH2Cl2. [source]

Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination Sphere and Spin Transition around Room Temperature

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2009
Birgit Weber
Abstract The reaction of iron(II) acetate with the tetradentate Schiff base like ligand H2L1 {[3,3,]-[4,5-dihydroxy-1,2-phenylenebis(iminomethylidyne)bis(2,4-pentanedion)]} leads to the formation of the complex [FeL1(MeOH)]. Reaction of this complex with pyridine (py) or N,N,-dimethylaminopyridine (dmap) leads to the two N4O2 -coordinated complexes [FeL1(py)2]·py (1) and [FeL1(dmap)2]·MeOH·0.5dmap (2). Both complexes are spin-crossover compounds that were characterised by using magnetic measurements, X-ray crystallography and temperature-dependent 1H NMR spectroscopy. Special attention was given to the role of the two hydroxy groups on the phenyl ring in the formation of a hydrogen-bonding network and the influence of this network on the spin-transition properties. Although only a gradual spin crossover was observed for both complexes, the transition temperature was shifted to higher temperatures relative to that of the complexes with no additional hydroxy groups at the Schiff base like ligand. The hydrogen-bonding network was responsible for this effect.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Magnetic, 57Fe Mössbauer, and IR Monitoring of the Thermal Spin Transition in a New Family of Iron(II) Spin-Transition Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003
Arno F. Stassen
Abstract A new family of iron(II) tetrafluoroborate and perchlorate spin-crossover compounds has been synthesised and is discussed. The iron(II) ion is surrounded by six 1-ethyltetrazole ligands, which are halogen-substituted on the C2 atom of the ethyl group. The spin-crossover temperatures T1/2 are high compared to the unsubstituted (1-alkyltetrazole)iron(II) complexes. The shape of the spin-transition curve (i.e. ,HS vs. T) varies largely over the different complexes and appears to be influenced neither by the crystal packing, nor by the electronic effects. The temperature-dependent spin-transition behaviour has been studied by magnetic susceptibility and by 57Fe-Mössbauer spectroscopy. These data have been supported by temperature-dependent mid-range infrared spectroscopy: the thermally induced spin transition has been observed by direct monitoring of the aromatic C,H stretching frequency. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]