Modeling copper(I) complexes: SIBFA molecular mechanics versus ab initio energetics and geometrical arrangements

SIBFA parametrization is extended to the closed-shell Cu(I) cation. This parametrization introduces the cation polarization up to quadrupolar effects and the metal-ligand charge transfer. The results obtained are compared to the corresponding ab initio quantum-chemical quantities given by intermolecular interaction energy decomposition and MP2 runs. Mono- and polycoordinated complexes of Cu(I) with O-, S-, and N-containing ligands are considered. An extension to systems containing two and three Cu(I) cations, found in copper metalloenzyme active sites, such as cytochrome C oxidase and hemocyanin, and supramolecular systems, is reported. The results obtained show that in such cases SIBFA is able to give geometrical arrangements in reasonable agreement with experimental data and interaction energy values close to those given by ab initio computations. With respect to MP2 results, covering interaction energy range of approximate to400 kcal/mol, the interaction energy rms amounts to 7.6 kcal/mol.