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  • 1
    Electronic Resource
    Electronic Resource
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 701-703 
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: We have studied the temperature variations of the EXAFS spectra of three Fe(II)/triazole-based spin transition polymeric compounds compared to a monomer belonging to the same family. These compounds have various temperatures of transition and hysteresis loop widths. In the three polymers, the Fe-Fe-Fe alignment, detected by a multiple scattering signal at the double Fe-Fe distance, is preserved through the spin transition. For the four compounds, we have studied the variations versus temperature of the Debye-Waller factors for both FeN6 (first shell) and Fe-Fe-Fe (multiple scattering path, only for the polymers). We report a strong increase of σ2(FeN6) through the spin transition for the monomer and two of the polymeric species. For the polymers an increase of σ2(Fe-Fe-Fe) is also observed. These observations confirm the results available in the literature, and we confirm the interpretation as an increase of the vibrational part of the DW. For one particular polymer, we observe an unexpected behaviour: no significant increase of the Debye-Waller factor from low spin to high spin states. The EXAFS study of these non mono-crystalline species is the only way to discuss the local structure-thermodynamics properties relationships, and particularly the so-called cooperative effect in the spin transition process.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-1948
    Keywords: Copper ; Magnetic properties ; Supramolecular chemistry ; Three-dimensional architecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel three-dimensional copper(II) compound of the formula [Cu3(btre)5(H2O)2](ClO4)6·H2O (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane) has been synthesized. The structure has been solved at 150 K by single-crystal X-ray analysis. The compound [C30H44Cu3N30O2·6(ClO4)·H2O] crystallizes in the triclinic space group P1bar with a = 12.488(1), b = 13.195(1), c = 19.756(2) Å, α = 78.959(8), β = 84.553(8), γ = 63.869(7)°, V = 2868.4(5) Å3, Z = 2 (trinuclear CuII units), 6484 reflections [I 〉 4σ(Ι)], RF = 0.0581, wR2 = 0.1214. The structure of this coordination polymer consists of a three-dimensional network built up from linear trinuclear CuII cations of formula [Cu3(btre)5(H2O)2]6+. This crystallographically independent unit comprises a linear array of three CuII ions linked by triple N1,N2-1,2,4-triazole bridges, yielding Cu1-Cu2 = 3.893(1) Å and Cu2-Cu3 = 3.889(1) Å. These linear trinuclear CuII units are linked by various pathways involving tridentate and tetradentate bridging btre ligands, which yields an unprecedented three-dimensional network. The CuII ions are weakly antiferromagnetically coupled with J = -1.01(2) cm-1 (based on the Hamiltonian: H = -J[SCu1·SCu2 + SCu2·SCu3] using the expression for the molar magnetic susceptibility S = 1/2 of a linear trinuclear system). The nature and the magnitude of the antiferromagnetic exchange have been discussed on the basis of the structural features.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-1948
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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