PRODUCTION AND CHARACTERIZATION OF METALLOFULLERENES

Negative ion/desorption chemical ionization mass spectrometry was used to characterize fullerenes with an encapsulated metal atom(s), metallofullerenes (M(x) @ C(n)), in arc-generated soot, pyridine extracts, and the extract residue. In agreement with results from other laboratories, the pyridine extracts of La2O3/graphite soot contain mostly La @ C82 and La2 @ C80, in addition to the "pure" (empty) fullerenes. However, the raw soot and the extract residue contain a broader range of metallofullerenes with relative abundances different from those observed from the extract (e.g., abundant La @ C60, La @ C70, and La @ C74). Arcing mixed-metal oxide-impregnated graphite rods yielded a mixed-metal dimetallofullerene (YLa @ C80) and higher relative abundances of metallofullerenes with the lower ionization potential metal atom. The thermal desorption behavior and solubility in different solvents of the doped and undoped fullerenes indicate an interaction between the C(n) and La(x) @ C(n) species. Finally, analysis of aqueous solutions of dried pyridine extracts of lanthana/graphite soot shows C(n) and La(x) @ C(n), which is consistent with the possible presence of metallofullerene/fullerene ionic complexes, (Lax @ Cn)+Cn-.