Complexes of ca(Ii), ni(ii) and zn(ii) with hemi-and dicarbahemiporphyrazines: Molecular structure and features of metal-ligand bonding

Abstract

Equilibrium geometry and electronic structures of Ca(II), Ni(II) and Zn(II) complexes with hemi-and dicarbahemi-porphyrazines were determined by DFT calculations at PBE0/pcseg-2 level followed by natural bond orbital (NBO) analysis of the electron density distribution. Electronic structures of Ni(II) complexes in ground and low-lying excited electronic states were determined by complete active space (CASSCF) method with following accounting dynamic correlation by multiconfigurational quasidegenerate second-order perturbation theory (MCQDPT2). According to data obtained by MCQDPT2 method the complexes of hemi-and dicarbahemiporphyrazine possess the ground states1A1 and3B1, respectively, and wave functions of the ground states have the form of a single determinant in the case of Ni(II) complex with hemiporphyrazine and the wave function for Ni(II) with dicarbahemiporphyrazine were found to possess a complex composition, therefore this complex could not be treated using single-reference DFT methods. The covalent component of metal-ligand bonding was found to increase significantly in the series: Ca(II) → Zn(II) → Ni(II). Large covalent contribution into Ni–N bonding is explained by additional LP(Np) → 3dx2-y2(Ni) and LP(Ni) → 3dx2-y2(Ni) inter-actions. The presence of agostic interactions-C–H∙∙∙Zn in the dicarbahemiporphyrazine complex was also confirmed.