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

The effect of solvent molecular features on the thermodynamics and kin etics of the sequential one-electron electroreduction of C60 was inves tigated in aprotic solvent systems of different polarity, polarizabili ty and viscosity. Interrelationships were established between experime ntal parameters, such as half-wave potentials and diffusion coefficien ts, and several solvent parameters. Low values of C60 diffusion coeffi cients determined in some solvents, particularly tetrahydrofuran, were interpreted in terms of solute aggregation. Solvent polarity and pola rizability 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 geomet ric factors. The geometric factor was related to the Stokes radii of t he reduced and oxidized forms of the solute and was demonstrated to co ntribute more significantly to the overall change of DELTAG(ET) than t he polarity factor. The calculated standard rate constants of the firs t two heterogeneous electron transfers, C-60(0/-) and C-60(-/2-), in b enzonitrile and dichloromethane were compared with published experimen tal values.