Electrochemical Studies on Vanadyl Complex with meso-5,10,15,20-tetrakis(2,5-Dimethoxyphenyl) porphyrin using Electron Paramagnetic Resonance and Cyclic Voltammetry

Abstract

The oxidation products of transition metal complexes with porphyrin are being examined currently by many research groups. meso- 5,10,15,20-tetrakis(2,5-Dimethoxyphenyl)porphyrin [T(2,5-(OCH3)2)PP] and its coordination compound with oxovanadium(IV) resulting in VO[T(2,5-(OCH3)2)PP] were prepared by the standard procedures. The resulting complex was characterized with or without the addition of antimony pentachloride by infrared (IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and cyclic voltammetry (CV). The UV-visible absorption spectrum of porphyrin ligand-based oxidation of vanadyl porphyrin VO[T(2,5-(OCH3)2)PP] in the presence of 0.5 mM SbCl5 has shown bands at 425, 540 and 650 nm. The final electro-oxidation product has a broad absorption band centered at 650 nm. It is characteristic of a porphyrin mono- cation which is seen due to oxidation at 0.0995V of ΔE value in the cyclic voltammogram of VO[T(2,5-(OCH3)2)PP]. These spectral features observed during the oxidation are in good agreement with the stepwise formation of mono-cation radical and di-cation. The EPR spectrum of VO[T(2,5-(OCH3)2)PP] suggests that it could be oxidized to the radical cation by oxidation with SbCl5 in dichloromethane. A radical cation is observed at low temperature and this spectrum corresponds to monomeric π-cation radical. A spectrum of fifteen lines is observed on the further addition of SbCl5 in dichloromethane. Thus, monomeric π-cation radical is recognized as [VO(TPP)]+. It is confirmed by the appearance of a new band at 1275 cm-1 in the IR spectrum. Zero field splitting (ZFS) was calculated from the triplet state on the EPR spectrum. It is suggested that ZFS interaction occurs from the dipolar coupling between the two electrons. Keywords: meso-Vanadyl porphyri