Complexes of Ca(II), Ni(II) and Zn(II) with Hemi- and Dicarbahemiporphyrazines: Molecular Structure and Features of Metal-Ligand Bonding

Equilibrium geometry and electronic structures of Ca(II), Ni(II) and Zn(II) complexes with hemiand 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 hemiand dicarbahemiporphyrazine possess the ground states A1 and B1, 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) interactions. The presence of agostic interactions -C–H∙∙∙Zn in the dicarbahemiporphyrazine complex was also confirmed.