Electronic properties of charged fullerenes characterized by EPR and Vis-NIR spectroscopy

EPR and Vis-NIR absorption spectra have both been measured for clarification of contradictory statements about the para- and diamagnetic states of fullerenes. Thereby identification of one sharp EPR signal in solution at room temperature to C-60(-) (g = 2.000 +/- 4.0001; Delta B = 0.07 +/- 0.01 mT) could be made upon using different fullerene sources (TechnoCarbo, Hoechst) and methods of anion generation (chemically, electrochemically, and photochemically). This fact is also supported by the similar observation for a monosubstituted derivative (g = 1.9999; Delta B = 0.10 mT), in which a small broadening of this sharp signal is found originating from additional H-1 hyperfine interactions. Furthermore the g-values of the radical anions of C-60 increase with charge (g(C-60(-)) < g(C-60(2-)) < < g(C-60(3-)) < g(C-60(5-))), indicating largest contributions from spin-orbit coupling for the monoanion. No diamagnetic states for the dianions of [60]- and [70]-fullerenes could be found so far but biradical species with largest zero field splittings D = 2.7 mT (C-60(2-)) and D = 3.1 mT (C-70(2-)), respectively. The cation formation of C-60 (g = 2.0023-2.0029; Delta B = 0.15-0.20 mT) with antimony pentachloride was controlled by mass spectrometry. Stable cations were found only in methylenechloride. In other solvents like toluene addition reactions seem to occur.