The mixed-valence states of biferrocene derivatives with long alkyl substituents, which have a layered structure, have been investigated by means of Fe-57 Mossbauer spectroscopy and X-ray powder diffraction. An interesting even-odd character in the number of carbon atoms of the alkyl chain is found in the relationship between the crystal structure and the mixed-valence state. The mixed-valence states of 1',1'''-bis(dodecyl)-1,1''-biferrocenium triiodide change in accordance with a transformation of the crystal structure in the solid state. An X-ray diffraction analysis for this salt obtained from dichloromethane at 0-degree-C showed that both the cation and the anion are situated at a centre of symmetry and the dodecyl substituent has the all-trans conformation. The layers are located in the ab plane.
