C5H5 on a Pt(111) surface:: Electronic structure and bonding

The chemisorption of cyclopentadienyl (c-C5H5) on Pt(111) has been studied using qualitative band-structure calculations in the framework of the tight-binding implementation of the extended Huckel method. We modeled the metal surface by a two-dimensional slab of finite thickness, with an overlayer of c-C5H5, one c-C5H5 per nine surface Pt atoms. The c-C5H5 molecule is attached to the surface with its five C atoms bonding mainly with three Pt atoms. The Pt-Pt bonds in the underlying surface and the C-C bonds of c-C5H5 are weakened upon chemisorption. Forward-donation from the adsorbate to the substrate is significant, and there is also substantial back-donation, as reported in the literature for benzene on Pt and Ni surfaces. We found that the band of Pt 5d(z)(2) orbitals plays an important role in the bonding between c-C5H5 and the surface, as do the Pt 6s and 6p(z) bands.