ELECTROREDUCTION OF BUCKMINSTERFULLERENE (C-60) IN APROTIC-SOLVENTS .2. ROLE OF SOLVATION

The effect of solvent molecular features on the thermodynamics and kinetics of the sequential one-electron electroreduction of C60 was investigated in aprotic solvent systems of different polarity, polarizability and viscosity. Interrelationships were established between experimental parameters, such as half-wave potentials and diffusion coefficients, and several solvent parameters. Low values of C60 diffusion coefficients determined in some solvents, particularly tetrahydrofuran, were interpreted in terms of solute aggregation. Solvent polarity and polarizability effects on reversible half-wave potentials were emphasized. The Gibbs energy of electron transfer DELTAG(ET) of the C-60(n-/(n+1)-) processes (n = 0, 1, 2, 3) was partitioned into polarity and geometric factors. The geometric factor was related to the Stokes radii of the reduced and oxidized forms of the solute and was demonstrated to contribute more significantly to the overall change of DELTAG(ET) than the polarity factor. The calculated standard rate constants of the first two heterogeneous electron transfers, C-60(0/-) and C-60(-/2-), in benzonitrile and dichloromethane were compared with published experimental values.