Electrochemically-Reversible, Single-Electron Oxidation of C60 and C70

Of special interest has been the cathodic electrochemistry of fullerenes, in part due to the observation of superconductivity for some of the triaionic states of C[sub 60]. While the cathodic electrochemistry has proven to be very rich, culminating last year in the observation of C[sub 60][sup 6], its anodic electrochemistry remains largely unexplored. To establish the chemical reversibility of the first oxidation wave of C[sub 60] and C[sub 70], the corresponding anodic and cathodic currents for this couple were measured as a function of the scan rate between 10 and 100 mV/s. The ratios determined (i[sub a]i[sub c]) were all equal to 1 within experimental error. Therefore, the cation radicals generated electrochemically are relatively long-lived on the voltammetric time scale at room temperature. The lifetime of the radicals can be estimated to be < 0.5 min. Most interestingly, scanning the potential more positive than that of the first reversible oxidation of C[sub 70] resulted in the observation of a second, one-electron oxidation of C[sub 70], C[sub 70][sup +] [yields] C[sub 70][sup 2+], at a potential of + 1.75 V. It is interesting to note that the potential difference between the first and the second anodic waves is 550 mV, closemore » to the values previously reported for the separations between consecutive cathodic waves of C[sub 60] and C[sub 70]. This second wave does not appear to be chemically reversible, as judged by preliminary cyclic voltammetric studies. Attempts to observe the second oxidation wave for C[sub 60] have not been successful. 14 refs., 1 fig.« less