DFT studies of copper complexes with biphenyldiimino dithioether. Part III: AIM analysis

The electronic structure of tetrabenza,e,g,k]-15,18-dithia-9,24-diaza-cyclohexadeca-9,23-diene (bite), as well as its quasi-tetrahedral and quasi-planar Cu(bite)^q complexes (q = +1 or +2), has been investigated at the MP2/6-31G level of theory in terms of atoms-in-molecule (AIM) topological analysis of electron density. The electron density ρ, its Laplacian L and bond ellipticity ε at bond critical points (BCP) as well as atomic volumes and atomic charges evaluated using the electron density integrated over atomic basins are correlated with the formal Cu oxidation state, coordination polyhedron geometry and mechanical strain data. The greatest changes in AIM parameters are concentrated at the central CuS₂N₂ part of the systems under study. The deformations of the electronic structure of the active center due to mechanical strain may be crucial for electron transfer. Atomic charges and bond strengths are compared with the results of natural bond orbital treatment.