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1 Materials Science

1 2003

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Spin crossover in a supramolecular feii-feiii system

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Ohta H. , Sunatsuki Y. , Ikuta Y. , Matsumoto N. , Lijima S. , Akashi H. , Kambe T. , Kojima M.

Materials Science

2003

tom Vol. 21, No. 2

191-198

The structure of [FeII(H3L)](ClO4)2ˇ3H2O, where H3L is a tripodal hexadentate ligand derived from the 1:3 condensation of tris(2-aminoethyl)amine and 4-formylimidazole, has been determined by X-ray crystallography at 113 and 293°K. A spin transition was indicated from the Fe-N bond distances. The temperature dependence of the magnetic susceptibility revealed that the complex undergoes a gradual spin transition in the temperature range 150-270°K. A mixed-valence complex, [FeII(H3L)][FeIII(L)](BF4)2 1.5H2O, was prepared by the controlled deprotonation of the protonated species, [FeII(H3L)](BF4)2ˇ1.5H2O, under aerobic conditions, and the X-ray structure was determined at 293°K. Two species, [FeII(H3L)]2+ and [FeIII(L)], are linked by imidazole-imidazolate (NH-N) hydrogen bonds to form a puckered sheet structure. Magnetic susceptibility measurements and Mössbauer spectra provided evidence of spin-crossover at both the FeII and FeIII sites. There are three accessible electronic states: (LS FeII-LS FeIII), (HS FeII-LS FeIII), and (HS FeII-HS FeIII) that occur in passing from lower to higher temperatures.