A topological model for predicting adsorption energies of polycyclic aromatic hydrocarbons on late-transition metal surfaces.

We introduce and validate by first-principles calculations an analogy between metal coordination chemistry and the adsorption of polycyclic aromatic hydrocarbons (PAHs) at metal surfaces for the derivation of a model for predicting the PAH adsorption energies. We correlate the binding of PAH on the metal surface with the coordination between metal atom and the ligands in the metal complex, where the formation enthalpy of metal complexes is mainly determined by the strength of a single metal-ligand (M-L) bond and by the number of the M-L bonds. This analogy allows estimation of the adsorption energies only on the basis of the structure of the PAHs and of their adsorption configurations. The adsorption energies of PAHs are found to depend on simple geometric parameters, such as the number of metal-carbon bonds. Moreover, when the lattice of the metal surface is commensurate with the size of benzene rings, the contribution to the adsorption energy from η-coordination is about twice that from η-coordination. These results show that the principles of coordination chemistry can facilitate the modeling of processes at metal surfaces, and pave the way to systematically model reactions involving complex adsorbates at surfaces.