Electronic structure and bonding of C 60 to metals

Abstract

The electron distribution and orbital interactions of C 60 with metals coordinated at different sites on the outside of the fullerene are evaluated with the Fenske-Hall molecular orbital method. The characters and nodal properties of the frontier orbitals of C 60 are first evaluated in terms of basis transformations to the C 2 units that join the pentagons and to the C 5 units of the pentagons in the C 60 molecule. The highest occupied molecular orbital (HOMO, h u symmetry) of C 60 is largely π bonding between the carbon atom pairs that join adjacent pentagons. The lowest unoccupied molecular orbital (LUMO, t 1u symmetry) is predominantly π antibonding between these carbon atom pairs. These orbital characters and energies are well situated for synergistic bonding of a metal atom to the carbon-carbon pair between the pentagons, in which the HOMO of C 60 donates σ electron density to the metal, and the LUMO of C 60 accepts π electron density from the metal. The electron donation and acceptance between the individual molecular orbitals of the C 60 molecule and the orbitals of a metal at different possible bonding sites of C 60 are probed with a Ag + ion. It is found that the bonding is favored at the site between the pentagons and that many different orbitals of C 60 are involved in the interaction. The net bonding of Ag + to C 60 is weaker than to ethylene. Calculations are also carried out on the organometallic complexes C 60Pt(PH 3) 2 and (C 2H 4)Pt(PH 3) 2. The net bonding of ethylene and C 60 to platinum is found to be very similar in these cases. A significant difference in this case is that the net negative charge on C 60 is more delocalized in the carbon cluster in contrast to the localized charge on ethylene.