ARE ENDOHEDRAL METAL (IV)C28 COMPOUNDS HYPERVALENT

Nonrelativistic and, where appropriate, scalar-relativistic linear combination of Gaussian-type orbital (LCGTO) local density functional (LDF) calculations on Ti@C28, Ce@C28, Ti@C28H4, Ce@C28H4, the corresponding empty fullerene C28, and the corresponding hydrogenated fullerene C28H4 are compared. The empty fullerene is tetravalent and strongly binds four hydrogen atoms on its exterior or a tetravalent atom inside. Combining a tetravalent endohedral atom with four exterior hydrogen atoms significantly weakens the two different sets of bounds and leads to an open-shell electronic structure.