Electron spin resonance spectra: geometrical and electronic structure of endohedral fullerenes

The ESR spectra of scandium-, yttrium-, and lanthanum-containing fullerenes (M@C-82, M=Sc, Y, La) are discussed. The first C-13 hyperfine structure has been analyzed in detail and at least seven electronically different groups of carbon atoms could be assigned by simulations of the ESR spectra. The strong similarity of the C-13 satel lite structure suggests the preference of one cage isomer for the scandium group C-82 endohedrals. The geometric structure and the electronic structure of all nine fullerene cage isomers of La@C-82 were studied by approximate density-functional-based theoretical calculations. A C-3v isomer was found as the most stable one. The manifold of C-13 hyperfine coupling constants could be interpreted on the basis of the calculated spin density distributions.