The relation between the mixed-valence state and crystal structure of iodide salts for 1′,1
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-bis(α- and β-naphthylmethyl)-1,1″-
biferrocenes has been studied by means of
57Fe Mössbauer spectroscopy and X-ray structural analysis. Time change of
57Fe Mössbauer spectroscopy was first observed for only the α-naphthylmethyl derivative; the trapped-valence state (metastable phase) of the Fe atom in the salt gradually changes into the detrapped-valence state (stable phase) on standing at room temperature for one month. There are two independent monocations in the β-naphthylmethyl derivative. Both salts (α-naphthylmethyl derivative in stable phase and β-naphthylmethyl derivative) gave the detrapped-valence state of
57Fe Mössbauer spectra, implying the equivalence of the oxidation state of the two Fe atoms. X-ray diffraction studies of both salts support the above results, i.e. both monocations sit on the center of symmetry and the Fe-C(Cp) distances (2.064(2) Å for the α-naphthylmethyl derivative and 2.061(9) and 2.056(7) Å for the β-naphthylmethyl derivative) are close to the mean values of ferrocene and ferrocenium ion.