Inorganic Chemistry, Vol.35, No.18, 5237-5243, 1996
Structural Distortion of the Vanadyltetraphenylporphine Anion-Radical Probed by Resonance Raman Spectroelectrochemistry
Electronic effects of one-electron reduction are investigated for (OV)TPP (vanadyltetraphenylporphine) by the use of spectroelectrochemical techniques. Cyclic voltammetry (CV), absorption, and resonance Raman (RR) spectroscopy of the anion radical are analyzed with the aid of isotope labeling and normal-coordinate analysis (NCA) in order to understand the structural changes. The first reported Q-band excitation RR spectra of the (OV)TPP anion radical provide important information regarding the structural distortion of the porphyrin ring upon one-electron reduction, through detection of A(2g) modes. Direct evidence for static distortion of the porphyrin ring is provided by the lowered depolarization ratios of the A(2g) modes. Moreover, the upshift of the nu(19) vibrational mode establishes that some of the C-alpha-C-m bonds are strengthened in the anion. Consideration of the molecular orbital pattern shows this observation to be consistent with a B-1g and not a B-2g Jahn-Teller distortion. The normal-mode calculation supports this inference.
Keywords:PI-CATION RADICALS;NORMAL-COORDINATE ANALYSIS;PORPHYRIN FORCE-FIELD;ZINC TETRAPHENYLPORPHYRIN;STRETCHING FREQUENCY;REDUCED PORPHYRINS;VANADYL PORPHYRINS;TRIPLET-STATES;ISOTOPE SHIFTS;SPECTRA