Paramagnetic states in pristine and metallofullerenes

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 differ markedly. 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 1017 spins/g, this is one unpaired electron per 1 000 to 10 000 fullerene molecules. able alternations of the concentrations of paramagnetic states and of the ESR linewidths can be observed with increasing treatment temperature above 300 °C at pure fullerenes. It is concluded that the structure of the paramagnetic states does change. The reason is the removal of oxygen. rmore ESR spectroscopy is used to characterize the electronic states of endohedral systems. Fullerenes produced in presence of lanthanum, scandium, holmium and yttrium show resolved ESR spectra in solutions and lanthanum, scandium and holmium already in the solid soot extract 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 these results different geometrical models of the investigated metallofullerenes can be predicted.