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

A porphyrin compound manganese(III) meso-5,10,15,20-tetrakis(4-pyridyl)porphyrin, Mn(Py)4P containing manganese(III) and 4-pyridyl ligands was synthesized. The UV-visible spectrophotometry and cyclic voltammetry were used to investigate the axial ligand and the redox behaviours of Mn(Py)4P. This study investigates the reduction properties of Mn(Py)4P using primary amine, imidazole and 2-methylimidazole as axial ligands. Reduction of Mn(Py)4P leads to a shift in absorption bands, indicating the conversion from manganese(III) to manganese(II) porphyrin. The addition of primary amine results in a square pyramidal structure for Mn(II) porphyrin, while imidazole or 2-methylimidazole leads to the formation of tetragonal complexes. These changes in geometry result in a decrease in π-bonding. The observed spectral patterns support the involvement of axial ligands in the 5th and 6th positions of manganese(III) porphyrin. The cyclic voltammogram confirmed the alteration in geometry, indicating changes in the redox properties of compound. As a whole, the results of this study provide light on the ways where the behaviour of in which Mn(Py)4P can be altered by the presence of other molecules.

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In this work, meso-tetrakis(p-Hydroxyphenyl) porphyrin [T(p-OH)PP] and manganese(III) meso-tetrakis(p-hydroxyphenyl) porphyrin Mn[T(p-OH)PP] were synthesized and characterized. The UV-visible and cyclic voltammetry were used to evaluate the axial ligand and redox behaviour of Mn[T(p-OH)PP]. The addition of ethylamine, diethylamine and tertiary amines to Mn(III) meso-porphyrins distinguishes their axial ligand characteristics. The presence of ethylamine causes the octahedral geometry to transform into a square pyramidal structure. Cyclic voltammetry shows that Mn(III) converts to Mn(II) porphyrins. Additionally, the UV-visible spectrophotometry and cyclic voltammetry were also used to investigate the oxidation process.