Electronic structure calculations of copper (II) complexes of [Cu(C10H8N2O4)(H2O)2] and [Cu(C10H8N2O4)(CH3OH)(H2O)]

Electronic structures of two copper complexes [Cu(C10H8N2O4)(H2O)2] (1) and [Cu(C10H8N2O4)(CH3OH)(H2O)] (2) which we just synthesized, have been studied by HF and DFT (B3LYP&B3PW91) calculations. The stable four- and five-coordinated geometries are obtained. It is noticed that relative stabilities of the both geometries are mainly affected by the intramolecular and intermolecular hydrogen bonding network. The contribution of intramolecular H-bond is favorable for the four-coordinated structure. However, when the intermolecular H-bond contribution is considered, the five-coordinated square-pyramid is definitely preferred. Conversion mechanism between four- and five-coordinated geometries is studied and then affirmed by IRC method. NBO charge distribution and the characteristics of frontier molecular orbitals of these complexes are also investigated. Furthermore, the experimental description related with calculations is given in Appendix A.