Metal-coated fullerenes C60Mn: Calculations for M = Be, Mg, Al and n=12, 20, 32

Semiempirical quantum-chemical PM3 calculations are reported for a relative ly new class of exohedral metallo-fullerenes - metal-coated or metal-covere d fullerenes: C60Mn The exohedral species were recently observed, however, their geometrical and electronic structure is not known yet. In this paper, relatively-even metal-atom distributions over the fullerene rings are cons idered - such regular forms are computed for M = Be, Mg, Al. Three selected stoichiometries are treated: C60M12, C60M20, and C60M32 The stoichiometrie s correspond to the location of the metal atoms above the twelve pentagons, above the twenty hexagons, and above each of the thirty two rings of C-60 This interesting arrangement over the rings is possible only for some types of atoms, while other elements are localized above bonds or atoms, or insi de the cage, or even react and destroy the cage. Other limitation comes fro m the parametrization of the computational methods - the computations are p erformed with the PM3 semiempirical method and metal-layer atomization heat s are used as a stability measure. Structural characteristics are presented , too. Considerable reductions of the cage symmetry are reported and their relationships to Jahn-Teller effect are discussed, too (no case of the icos ahedral symmetry is found).