SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL PROPERTIES OF A NEW SERIES OFUNSYMMETRICAL BIS(PHENOXO) BRIDGED MACROCYCLIC BINUCLEAR MANGANESE(III) COMPLEXES

A new series of binuclear bis(phenoxo) bridged manganese(III) complexe s with dissimilar co-ordination environments have been prepared. The m acrocyclic ligands have two different compartments, one has two unsatu rated nitrogen and the other two saturated nitrogen donor atoms. The t wo phenoxide oxygens are common to both manganese(III) ions. Two reduc tion couples were observed for all the complexes in the negative poten tial region (0.00 to - 1.60 V) [Mn-2(III) --> (MnMnIII)-Mn-II --> Mn-2 (II)]. 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 [Mn -2(III) --> (MnMnIV)-Mn-III --> Mn-2(IV)]. The first one electron oxid ation is observed around +0.25 V and the second around +0.60 V. The fi rst one electron reduction potential mainly depends upon the ring size , substituent at the para position to the phenoxide oxygen in the liga nd system and axially bound halide ions. In the positive potential reg ion the first one electron oxidation potential is less sensitive to ri ng size variation and varies with the axially bound halide ion.