C₅H₅on 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 Hückel 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 5dz2 orbitals plays an important role in the bonding between c-C5H5 and the surface, as do the Pt 6s and 6pz bands.