PARAMAGNETIC STATES IN PRISTINE AND METALLOFULLERENES

Most pristine fullerenes give very weak ESR signals. The ESR spectra o f soot extract and of the C-60, C-70 and higher fullerene fractions sh ow signals of the same ESR linewidths of 0.1 mT but the spin concentra tions differ markedly. The lowest spin concentration is found in the s oot extract. After different temperature treatments the spin concentra tion increases. In pure C-60 and C-70 material the spin concentration is about 10(17) spins/g, this is one unpaired electron per 1 000 to 10 000 fullerene molecules. Remarkable alternations of the concentration s of paramagnetic states and of the ESR linewidths can be observed wit h increasing treatment temperature above 300 degrees C at pure fullere nes. It is concluded that the structure of the paramagnetic states doe s change. The reason is the removal of oxygen. Furthermore ESR spectro scopy is used to characterize the electronic states of endohedral syst ems. Fullerenes produced in presence of lanthanum, scandium, holmium a nd yttrium show resolved ESR spectra in solutions and lanthanum, scand ium and holmium already in the solid soot extract which can be interpr eted in terms of hyperfine coupling of an unpaired fullerene electron with the nuclear magnetic moments of the metal atoms. In some cases tw o species of the same metallofullerenes can be observed. Using these r esults different geometrical models of the investigated metallofullere nes can be predicted.