Interaction between metallic p orbitals and the pi orbitals of organic molecules: The binding between ethylene and aluminum

A set of first principles calculations has been performed to characterize t he interaction of a pi bonded organic molecule with a simple s-p metal surf ace. The structures of the Al(C2H4) and [AI(C2H4)](+) complex molecules, an d of the adsorption of an isolated ethylene molecule onto Al(100) were calc ulated. We find a C(2)H(4)pi-->Al3p interaction to be the most significant in Al(C2H4) and [Al(C2H4)](+) with additional Al 3p --> C(2)H(4)pi* back-do nation in Al(C2H4). In complete contrast, no chemical binding of ethylene t o Al(100) is observed, but physisorption is predicted. These calculations s how how the binding between a pi bond and the pi orbitals of a simple metal atom cannot be extended to describing the binding with a p band of a solid . Our conclusions may be extended to other systems where this interaction c ould be significant.