ELECTRONIC-STRUCTURE AND BONDING OF C-60 TO METALS

The electron distribution and orbital interactions of C60 with metals coordinated at different sites on the outside of the fullerene are eva luated with the Fenske-Hall molecular orbital method. The characters a nd nodal properties of the frontier orbitals of C60 are first evaluate d in terms of basis transformations to the C2 units that join the pent agons and to the C5 units of the pentagons in the C60 molecule. The hi ghest occupied molecular orbital (HOMO, h(u) symmetry) of C60 is large ly pi bonding between the carbon atom pairs that join adjacent pentago ns. The lowest unoccupied molecular orbital (LUMO, t1u symmetry) is pr edominantly pi antibonding between these carbon atom pairs. These orbi tal characters and energies are well situated for synergistic bonding of a metal atom to the carbon-carbon pair between the pentagons, in wh ich the HOMO of C60 donates sigma electron density to the metal, and t he LUMO of C60 accepts pi electron density from the metal. The electro n donation and acceptance between the individual molecular orbitals of the C60 molecule and the orbitals of a metal at different possible bo nding sites of C60 are probed with a Ag+ ion. It is found that the bon ding is favored at the site between the pentagons and that many differ ent orbitals of C60) are involved in the interaction. The net bonding of Ag+ to C60 is weaker than to ethylene. Calculations are also carrie d out on the organometallic complexes C60Pt(PH3)2 and (C2H4)Pt(PH3)2. The net bonding of ethylene and C60 to platinum is found to be very si milar in these cases. A significant difference in this case is that th e net negative charge on C60 is more delocalized in the carbon cluster in contrast to the localized charge on ethylene.