REVERSIBLE FULLERENE ELECTROCHEMISTRY - CORRELATION WITH THE HOMO-LUMO ENERGY DIFFERENCE FOR C-60, C-70, C-76, C-78, AND C-84

Reversible one-electron oxidations and reductions have been observed by Osteryoung square wave voltammetry (OSWV) for the three higher fullerenes C-76, C-78, and C-84 in 1,1,2,2-tetrachloroethane (TCE) containing 0.1 M tetrabutylammonium hexafluorophosphate ((TBA)PF6). Potentials are reported versus the internal ferrocene redox couple. Under these conditions C-76 displays a reversible oxidation at 0.81 V, an irreversible oxidation at 1.30 V, and two reversible reductions at -0.83 and -1.12 V. The oxidations of C-78 show evidence of two species, which is consistent with the proposed isomerism for C-78 The predominant C-78 species shows a reversible oxidation at 0.95 V, an irreversible oxidation at 1.43 V, and two reversible reductions at -0.77 and -1.08 V. The minor species displays a reversible oxidation at 0.70 V and an irreversible oxidation at 1.17 V, while the reductions seem to coincide with those of the other isomer. Finally, C-84 yielded an oxidation at 0.93 V and three reversible reductions at -0.67, -0.96, and -1.27 V. A comparison of the differences in potential of the first reduction and first oxidation, (E(ox) - E(red)), shows that this difference becomes generally smaller as fullerene size increases, with the exact order being C-60 > C-70 > C-78(C-2v) > C-76 > C-84 > C-78(D-3) The experimental (E(ox) - F-red) differences correlate well with calculated HOMO-LUMO separations for a series of five fullerenes.