New EPR signals of endohedral metallofullerenes

The EPR spectra of endohedral metallofullerenes (EMF), La-EMF and Y-EMF, which were free of admixtures of C-60 and of other empty fullerenes, were examined. Endohedral metallofullerenes were prepared by extraction of fullerene-containing soots with DMF. New signals with g factors close to those of fullerene radical anions were observed in the EPR spectra of solutions of EMF in DMF and DMSO. At similar to 20 degreesC, these signals are observed as a doublet (DeltaH(pp) approximate to 0.04 mT) and singlet (DeltaH(pp) approximate to 0.01 mT) in solutions of La-EMF and Y-EMF, respectively. These EPR signals belong to solvated La@C-82 and Y@C-82 molecules and are characterized by small hyperfine interaction constants a(M) due to a substantial decrease in the spin density of the unpaired electron at the metal atom.