Synthesis, spectral and electrochemical properties of a new series of unsymmetrical bis(phenoxo) bridged macrocyclic binuclear manganese(III) complexes

Abstract

A new series of binuclear bis(phenoxo) bridged manganese(III) complexes with dissimilar co-ordination environments have been prepared. The macrocyclic ligands have two different compartments, one has two unsaturated nitrogen and the other two saturated nitrogen donor atoms. The two phenoxide oxygens are common to both manganese(III) ions. Two reduction couples were observed for all the complexes in the negative potential region (0.00 to –1.60 V) [MnIII2 → MnIIMnIII → MnII2]. The first one electron reduction is observed around –0.90 V and the second around –1.30 V. In the positive potential region (0.00 to +1.00 V) two oxidation couples are observed for all the complexes [MnIII2 → MnIIIMnIV → MnIV2]. The first one electron oxidation is observed around +0.25 V and the second around +0.60 V. The first one electron reduction potential mainly depends upon the ring size, substituent at the para position to the phenoxide oxygen in the ligand system and axially bound halide ions. In the positive potential region the first one electron oxidation potential is less sensitive to ring size variation and varies with the axially bound halide ion.