Geometric and electronic structures of 5,10,15,20-tetraphenylporphyrinato Palladium(II) and Zinc(II): Phenomenon of Pd(II) complex

Abstract

The structure of PdTPP and ZnTPP molecules have been studied at first time by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) complemented by quantum-chemical calculations. Four conformers have been found in which four phenyl fragments are turned in different directions from their perpendicular position relative to the porphyrin plane. The structures with turned orientation of phenyl fragments demonstrate an energy balance between orbital conjugation of phenyls with porphyrin framework and steric repulsion of the phenyl and pyrrole fragments. Comparison of PdTPP and unsubstituted PdP as well as ZnTPP and ZnP complexes within the framework of NBO analysis shows that characteristics of the MN coordination bond do not practically change when meso-substituents are introduced. In contrast, the Cα-Cm bond lengths at the meso-substituent, the Cα-Cm-Cα bond angle, and the energy of the frontier orbitals are changed significantly. The change in these parameters indicates the electron-donor nature of the phenyl fragments. Strong donor-acceptor interactions between LP(N) and both 4dx2-y2 and 5s AO (Pd) causes a significant transfer of the electron density from the donor atom N on Pd resulting the extremely low effective net charge on the palladium atom and determining the high donor and acceptor properties of PdP and PdTPP complexes.