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The effects of zero-point energy and counterion on the rate of intramolecular electron transfer in mixed-valence biferrocenium salts are investigated. All asymmetrically substituted biferrocenium triiodide salts, where the substituent is either 1'-ethyl (9), 1'-butyl (IO), I'-acctyl (ll), 1'-butyryl (12), or 1'-ethyl 6'-propyl (13), are found to be localized on the Miwsbauer, EPR, and IR time scales. In 300 K Miwsbauer spectra they each show two doublets, one for Fe" metallocene and the other for Fell' metallocene (electron-transfer rates less than -IO7 s-'). The cation in each of compounds e 1 3 is not symmetric; that is, the two irons are not in equivalent environments. This asymmetry induces a nonzero zero-point energy barrier for intramolecular electron transfer. The effects on the rate of electron transfer of replacing 13by picrate (14), IBrF (IS), and PF6-(16) in 2 are also examined. Replacing 13by picrate and IBr, leads to a decrease in the rate of electron transfer. The Miwsbauer spectrum taken at 300 K for 14 consists of two doublets. In other words, the electron-transfer rate of 14 is less than -lo7 s-l. In the case of 15, the variable-temperature (100-275 K) Miwsbauer spectra exhibit a localized electronic structure. The PFC salt is converted from valence trapped at low temperatures to valence detrapped above 280 K. The difference in electron-transfer rates can be explained by the magnitude of the energy barrier of charge oscillation in anions and cation-anion interactions. Hendrickson, D. N.; Oh, S. M.; Dong, T.-Y.; Kambara, T.; Cohn, M. J.; Moore. M. F. Comments Inorg. Chem. 1985, 4 (6), 329. Dong, T.-Y.; Cohn, M. J.; Hendrickson, D. N.; Pierpont, C. G. J. Am. Chem. Soc. 1985, 107, 4777. Cohn, M. J.; Dong, T.-Y.; Hendrickson, D. N.; Geib, S. J.; Rheingold, A. L. J . Chem. SOC., Chem. Commun. 1985. 1095. Dong, T.-Y.; Hendrickson, D. N.; Iwai, K.; Cohn, M. J.; Geib, S. J.; Rheingold, A. L.; Sano, H.; Motoyama, 1.; Nakashima, S . J. Am. Chem. SOC. 1985. 107, 7996. Iijima, S.; Saida, R.; Motoyama, 1.; Sano, H. Bull. Chem. SOC. Jpn. 1981, 54, 1375. Nakashima. S.; Masuda, Y.; Motoyama, I.; Sano, H. Bull. Chem. Soc. Jpn. 1981, 60, 1673. Nakashima, S.; Katada. M.; Motoyama, I.; Sano, H. BUN. Chem. Soc. The binding structures of enantiomeric and racemic [M(phen)J2+ (M = Ru, Fe; phen = ],IO-phenanthroline) complexes withsodium montmorillonite were studied by means of X-ray diffraction and electric dichroism measurements. The electron density curves along the c axis of a clay layer were determined for the powder samples of clay-chelate adducts. At maximum adsorption, the enantiomeric and racemic chelates formed the single-molecular and double-molecular layers in the interlayer spaces, respectively. The reduced linear dichroisms for the two characteristic bands in their electronic absorption spectra (Le. the metal-to-ligand charge-transfer band at 400-500 nm and the ligand excitation bands at 240-280 nm) were determined for the bound metal complexes in a colloidal state. The orientation of a bound complex was el...

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