ELECTROCHEMICAL GENERATION AND ELECTRON-PARAMAGNETIC-RESONANCE STUDIES OF C-60(-), C-60(2-), AND C-60(3-)

The -1, -2, and -3 anions of C-60 were generated electrochemically in 4:1 toluene-acetonitrile. The visible/near-IR spectra were monitored in situ. Square wave voltammograms and electronic spectra showed that after bulk electrolysis to produce the anions, the following percentages of the starting C-60 concentration could be reoxidized to neutral C-60 in typical data sets: -1 anion, 75%; -2 anion, 66%; -3 anion, 46%. Continuous wave (CW) electron paramagnetic resonance (EPR) spectra of the -1 and -3 anions exhibited broad signals that were temperature dependent. The averaging of anisotropy of the signals between 15 and 60 K is attributed to dynamic Jahn-Teller distortion. Electron spin-echo and saturation recovery EPR data for the -1 anion at 10 and 16 K showed that the electron spin relaxation rates are dependent upon position in the spectrum, which is attributed to variations in the Jahn-Teller distortion. For both the -1 and -3 anion above about 70 K the CW line shape of the EPR signal is electron spin-lattice relaxation rate determined. The EPR data indicate that the -2 anion is diamagnetic. The sharp signals that are observed with varying intensity in the spectra of the -1, -2, and -3 anions have much slower electron spin-lattice relaxation rates than the signals for the -1 and -3 anions. The line shapes for the sharp signal(s) are largely independent of temperature. These signals are assigned to as-yet unidentified species with lower symmetry and slower molecular rotation than the C-60 anions.