Density functional theory predictions for the binding of transition metal cations to pi systems: from acetylene to coronene and tribenzocyclyne

The Becke-3 Lee-Yang-Parr (B3LYP) density functional is employed in the det ermination of the structures, binding energies, and vibrational frequencies for the complexes of water, acetylene, ethylene, benzene, C12H6, coronene, and tribenzocyclyne with the first row transition metal cations from Ti th rough Cu. For the smaller ligands, comparison with the available experiment al and theoretical data delineates the accuracy of the B3LYP functional for this type of complex. For acetylene and ethylene, new coupled cluster resu lts provide supplementary comparisons. The B3LYP binding energies are gener ally within 5 kcal/mol of the corresponding coupled cluster single double ( triple) and experimental estimates. The metal coronene binding energies are on average 5 kcal/mol greater than those for the metal benzenes, due simpl y to the increased polarizability of the ligand. In contrast, the metal ion s are much more strongly bound to tribenzocyclyne and C12H6 than to either benzene or coronene (e.g. by 50 kcal/mol). This enhanced binding is related to the large central cavity, which allows for a closer approach of the met al ion to the ligand plane, In fact, the Ni and Cu ions insert directly int o the cavity, forming a planar complex, in reasonable agreement with the po stulates of an experimental study of Dunbar and co-workers. (C) 2000 Elsevi er Science B.V.