Geometrical and Electronic Structure of Fluorinated and Non-fluorinated Platinum(II) Tetraphenylporphyrin Complexes.

Abstract

The composition of the saturated vapors of two platinum com-plexes with the macrocyclic ligands 5,10,15,20-tetraphenyl-porphyrin (PtTPP) and 5,10,15,20-tetrakis(pentafluoro-phenyl)-por-phyrin (PtTF5PP) and their structures were determined by syn-chronous gas-phase electron diffrac-tion/mass spectrometry (GED/MS). These porphyrin com-plexes are those with the heaviest metal atom in the coordination cavity that have been structurally investigated in the gas phase. The mass spectra confirm the presence of a single molecular form of each, PtTPP (T=629 K) and PtTF5PP (T=597 K). Their structures can serve as references for related com-plexes in the crystalline state or solutions. Differences between the geometries of PtTPP and PtTF5PP in the crystalline and gaseous states include a significant deformation of the tetrapyrrole macro-cycle in solid PtTPP. The experimental Pt-N bond lengths of both complexes are in agreement with quantum chemical calculations (DFT/B97D/ECP(Pt)) taking into account relativistic effects. The effect of lanthanide contraction is evident from the similarity of the Pd-N and Pt-N internuclear distances of analogous compounds. The strong electron density transfer from the porphyrin backbone to the metal ion and the resulting low effective positive charge on the platinum atom, studied by NBO and QTAIM methods, helps to rationalize the high catalytic activity of such platinum compounds.