Thermodynamics of Fullerenes Reduction Revisited

Abstract

The thermodynamics of fullerene C60 electroreduction, and 2′-ferrocenylpyrrolidino [3′,4′;1,2][C60]fullerene electroreduction and electrooxidation has been studied in different aprotic solvents containing tetra(alkyl)ammonium perchlorates as supporting electrolytes using dc cyclic voltammetry and square-wave voltammetry. Obtained values of formal potential were corrected for diffusion potential drop. The electrode processes of C60 reduction are accompanied by the ion pair formation. In each reduction step, one cation of supporting electrolyte is involved. The strength of ionic interaction increase with decrease in the interacting ions size. The association constant of ion pair formation, Ka, also depends on the solvent dielectric constant. A linear relationship between ln Ka and 1/ɛs has been found. The association constants obtained on the base of these relations depend on the solvents dielectric properties. The influence of ion pair formation process on the reduction and oxidation of 2′-ferrocenylpyrrolidino [3′,4′;1,2][C60]fullerene has also been compared. Both, anion formed during fullerene cage reduction and cation produced during ferrocene moiety oxidation are associated with one counter-ion from supporting electrolyte. The cation formed during oxidation much stronger interacts with perchlorate ions in comparison to the anion formed by electroreduction. The influence of ion pair formation on the donor-acceptor energy gap has been also discussed.