Paramagnetic states in pristine and metallofullerenes

Summary form only given. Most pristine fullerenes give very weak ESR signals. The ESR spectra of soot extract and of the C-60, C-70 and higher fullerene fractions show signals of the same ESR linewidths of 0.1 mT but the spin concentrations are quite different. The lowest spin concentration is found in the soot extract. After different temperature treatments the spin concentration increases. In pure C-60 and C-70 material the spin concentration is about 10/sup 17/, this is one unpaired electron per 1 000 to 10 000 fullerene molecules. Remarkable alternations of the concentrations of paramagnetic states and of the ESR linewidths can be observed with increasing treatment temperature above 300/spl deg/C at pure fullerenes. It is concluded that the structure of the paramagnetic states does change. The reason is the removal of oxygen. Furthermore ESR spectroscopy is used to characterize the electronic states of endohedral systems. Fullerenes produced in presence of Lanthanum, Holmium, Scandium and Yttrium show well resolved ESR spectra in solutions which can be interpreted in terms of hyperfine coupling of an unpaired fullerene electron with the nuclear magnetic moments of the metal atoms. In some cases two species of the same metallofullerenes can be observed. Using this results different geometrical models of the investigated metallofullerenes are considered.