c-C5H5 on a Ni(1 1 1) surface: Theoretical study of the adsorption, electronic structure and bonding

In the present work the ASED-MO method is applied to study the adsorption of cyclopentadienyl anion on a Ni(1 1 1) surface. The adsorption with the centre of the aromatic ring placed above the hollow position has been identified to be energetically the most favourable. The aromatic ring remains almost flat, the H atoms are tilted 17° away from the metal surface. We modelled the metal surface by a two-dimensional slab of finite thickness, with an overlayer of c-C₅H₅⁻, one c-C₅H₅⁻ per nine surface Ni atoms. The c-C₅H₅⁻ molecule is attached to the surface with its five C atoms bonding mainly with three Ni atoms. The NiNi bond in the underlying surface and the CC bonds of c-C₅H₅⁻ are weakened upon adsorption. We found that the band of Ni 5dz² orbitals plays an important role in the bonding between c-C₅H₅⁻ and the surface, as do the Ni 6s and 6p_z bands.