Electrochemical Studies on Manganese (III) Complex with meso-5, 10, 15, 20-Tetrakis (o-nitrophenyl) porphyrin by Cyclic Voltammetry and UV-Visible Spectrophotometry

Abstract

Meso-5,10,15,20-Tetrakis(o-nitrophenyl)porphyrin, [T (o-NO2)PP] and manganese (III) meso-5,10,15,20- Tetrakis(2,5-dimethoxyphenyl)porphyrin, Mn[T(o- NO2)PP] have been prepared. The Mn[T(o-NO2)PP] complex is characterized by UV-Vis spectrophotometric and cyclic voltametric (CV) studies. The preparation of Mn(III) porphyrin complex may be attributed due to a significant metal-porphyrin π interaction. In Mn(III) porphyrin, Mn is in a high spin d4 configuration with octahedral geometry. Mn(III) porphyrin geometry has been altered to square pyramidal Mn(II) porphyrin after addition of ethylamine. In square pyramidal Mn(II) porphyrin, Mn atom is in a high-spin d5 configuration with the occupied d(x 2 - y 2 ) orbital whose orbital energy is low. This shows that Mn(III) will be out of the plane of porphyrin. Successive addition of diethylamine, Mn(III) porphyrin geometry has been changed to tetragonal complex due to a weak π back bonding. It appears that π -bonding is lowered when the tetragonal complexes are formed. This might arise due to the expansion of the in-plane metal to porphyrin in a direction to occupy two axial ligands of ethylamine. The geometry changes indicate that the two ethyl amines groups occupy 5th and 6th places as axial coordination site due to the availability of two ethylamine from ethyl, diethyl and triethyl amines. Cyclic voltammogram confirmed the oxidation state and reduction behavior of Mn porphyrin complex.