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Issue 9, 2007
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Spin crossover behavior in a family of iron(II) zigzag chain coordination polymers

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Abstract

The paper reports the synthesis and detailed characterization of two new Fe(II) compounds: [Fe(pyim)2(bpen)](ClO4)2·2C2H5OH (2) and [Fe(pyim)2(bpe)](ClO4)2·C2H5OH (3) (pyim = 2-(2-pyridyl)imidazole, bpen = 1,2-bis(4-pyridyl)ethane, and bpe = 1,2-bis(4-pyridyl)ethene). Both compounds and the earlier synthesized [Fe(pyim)2(bpy)](ClO4)2·2C2H5OH (1) (bpy = 4,4′-bipyridine) form a family of one-dimensional spin crossover coordination polymers. Variable-temperature magnetic susceptibility measurements and Mössbauer spectroscopy have revealed rather gradual spin transitions centered at 176 and 198 K for 2 and 3, respectively. The fitting of magnetic properties with the regular solution model leads to the enthalpy and entropy of spin transitions and the cooperativity parameter equal to ΔH = 12.3 kJ mol−1, ΔS = 68.5 J mol−1 K−1, Γ = 1.80 kJ mol−1 for 2 and ΔH = 13.6 kJ mol−1, ΔS = 68.1 J mol−1 K−1, Γ = 2.05 kJ mol−1 for 3. The crystal structures of 2 and 3, resolved by X-ray diffraction at 293 K, belong to the monoclinic space group C2/c (Z = 4). Both compounds display a one-dimensional infinite zigzag-chain structure. The polymer chains are stacked into two-dimensional sheets through intermolecular π-interactions. The crystal packing of both compounds encloses two kinds of channels in which the counter ions and ethanol molecules are inserted. The DFT calculations of binuclear fragments extracted from three polymers resulted in the energy gaps between the LS and HS states being ordered as the observed transition temperatures. The influence of bridging ligands in the studied family of compounds was found in the modulation of the energy gap between the LS and HS states, leading to different transition temperatures.

Graphical abstract: Spin crossover behavior in a family of iron(ii) zigzag chain coordination polymers

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Publication details

The article was received on 24 Oct 2006, accepted on 10 Jan 2007 and first published on 23 Jan 2007


Article type: Paper
DOI: 10.1039/B615410G
Dalton Trans., 2007, 934-942

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    Spin crossover behavior in a family of iron(II) zigzag chain coordination polymers

    G. S. Matouzenko, M. Perrin, B. Le Guennic, C. Genre, G. Molnár, A. Bousseksou and S. A. Borshch, Dalton Trans., 2007, 934
    DOI: 10.1039/B615410G

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