Structural and thermal characteristics of an amorphous iodine complex of a ferrocenylenesilylene polymer, [-(C 5 H 4 )Fe(C 5 H 4 )Si(CH 3 )(C 6 H 5 )‚(I 1.5 )-] n , have been measured using 57 Fe Mo ¨ssbauer, IR and Raman spectroscopy, X-ray diffraction, and thermomechanical analysis. The iodine-doped macromolecules are mixed-valence salts with a localized electron structure on the 57 Fe Mo ¨ssbauer time scale, in which ferrocenylene units and ferrocenium moieties coexist. These macromolecules consist of blocks containing ferrocenium moieties and sequences of nonoxidized ferrocenylene units. The environment about the ferrocenium moieties consists of both single I 3and polyiodide [I 3 ] -‚nI 2 species. Mo ¨ssbauer data, collected in the range 5-300 K, are interpreted in terms of the temperature dependence of the Lamb-Mo ¨ssbauer factor and reversible electron transfer with an activation energy of 4.7 kJ/mol. The transformations of [I 3 ] -+ I 2 clusters to I 3are proposed to accompany Fe(II)-Fe(III) oxidation.