MIXED-VALENCE BIFERROCENIUMS - PRONOUNCED EFFECTS OF CATION-ANION INTERACTIONS ON THE INTRAMOLECULAR ELECTRON-TRANSFER RATE

Relatively minor perturbations caused by the cation-anion interactions in 1',2',3',1''',2''',3''' hexaethylbiferrocenium triiodide (1) and 1',2',4',1''',2''', 4'''-hexaethylbiferrocenium triiodide (2) have pronounced effects on the electronic structure and the rate of intramolecular electron transfer. The X-ray structure of 1 has been determined at 298 K: P2(1)/c, a = 9.433(3) Angstrom, b = 18.591(3) Angstrom, c = 10.425(3) Angstrom. beta = 110.24(2)degrees, Z = 2, D-calcd = 1.779 g cm(-3), R(F) = 0.037, and R(wF) - 0.035. The isomeric 2 crystallizes in the monoclinic space group P2(1)/n with two molecules in a unit cell with dimensions a = 12.214(9) Angstrom, b = 11.516(10) Angstrom, c = 12.222(7) Angstrom. beta = 103.36(5)degrees; R(F) = 0.055, and R(wF) = 0.055. The neutral compound 1',2',3',1''',2''',3'''-hexaethylbiferrocene crystallizes in the triclinic space group P1 with one molecule in a unit cell with dimensions a = 7.999(1) Angstrom, b = 8.981(3) Angstrom, c = 11.222(2) Angstrom. alpha = 112.08(2)degrees, beta = 76.47(1)degrees, gamma = 113.80(2)degrees; R(F) = 0.027, and R(wF) = 0.032. The variable-temperature Fe-57 Mossbauer data indicate that 1 is delocalized on the Mossbauer time scale in the solid state above 170 K. However, the electron-transfer rate in 2 is localized on the Mossbauer time scale at 300 K (electron-transfer rate <similar to 10(7) s(-1)). We suggest that the difference in rates of electron transfer in 1 and 2 is a result of difference in the cation-anion interactions. A comparison of electron-transfer rates in solid state and solution state is also presented.