Molecular Orbital Model for Pyridine/α-Pyridyl Adsorption on Metal Surfaces

Electronic density functional calculations were used to explain the proposed formation of α-pyridyl from pyridine on silver, copper, cadmium, and gold surfaces. Our results show that the formation of α-pyridyl is governed by the mixing of metal wavefunctions with pyridine's near-HOMOs. When the organic orbitals mix with metal sp - character, a bonding interaction results and pyridine is the dominant surface species. If the metal orbitals mixing most strongly with the pyridine near-HOMOs are of d-character then an antibonding or nonbonding interaction results and α-pyridyl is the dominant surface species. A predicted correlation between the ratio of the concentration of the two surfaces species and the applied electrode potential is supported by analysis of surface-enhanced Raman data.