ELECTRON-TRANSFER IN MIXED-VALENCE POLYFERROCENIUM CATIONS - PREPARATION, ELECTROCHEMISTRY, AND FE-57 MOSSBAUER CHARACTERISTICS

Convenient new methods are developed for the preparation of 1',1'''''- disubstituted triferrocenes and tetraferrocenes that can be oxidized w ith iodine to a new series of mixed-valence compounds. The X-ray struc tures of 1', 1'''''-diethyltriferrocene, 1',1'''''-dimethoxymethyltrif errocene, and 1', 1'''''-dimethoxymethyltetraferrocene have been deter mined at 298 K. The rates of intramolecular electron transfer in these mixed-valence cations were estimated by variable-temperature Fe-57 Mo ssbauer experiments. The features in all 80 and 300 K spectra include two doublets, one with a quadrupole splitting (Delta E-Q) of similar t o 2 mm s(-1) (Fe(II) site) and the other with Delta E-Q = similar to 0 .3 mm s(-1) (Fe(III) site). This pattern of two doublets is expected f or a mixed-valence biferrocenium cation that is valence-trapped on the time scale of the Mossbauer technique (electron-transfer rate < simil ar to 10(7) s(-1) in the solid state). The electrochemical measurement s are also presented.