Out-of-plane C m H vibrations and electronic structure of Zn complexes of porphyrins and their π anions

Abstract

Based on the calculation of frequencies of the normal vibrations of Zn complexes of octaalkylporphyrins (Zn-OAPs), Zn porphin (Zn-P), and their meso-deuterated derivatives by the method of density functional theory (B3LYP/6–31G(d, B3LYP/6–311+G(d)), a new interpretation of CmH(D) out-of-plane deformation vibrations of porphyrins is proposed. It is shown that the vibration patterns of these modes are characterized by high contributions (>90%) of the coordinates of displacement out of the macrocycle plane of the H(D) atoms in meso positions. At the same time, a small change in the vibration pattern of such a mode in the d4 isotopomer (∼5%) is accompanied by a large change in its intensity. The geometry of free π anionic forms of Zn-OAPs and Zn-P and their complexes with cations Na+ and K+ is optimized, and the normal vibrations of these compounds are calculated. A comparison with experimental IR spectra of solid samples shows that anion-cation complexes form under these conditions. The interaction with cations lowers the symmetry of the nuclear skeleton of reduced forms of Zn-OAPs, considerably decreases their charge, and markedly affects the structure of this skeleton and its vibrations.