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 dicarbahemiporphyrazines 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 states 1 A 1 and 3 B 1 , 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) → 3d x 2 -y 2 (Ni) and LP(Ni) → 3d x 2 -y 2 (Ni) interactions. The presence of agostic interactions -C-H•••Zn in the dicarbahemiporphyrazine complex was also confirmed.