Binuclear Metal Complexes. XLII. Manganese(IV) Complexes Synthesized by Oxidation of Binuclear Manganese(II) Complexes of 2-(Salicylideneamino)phenols with Tetrachloro-o-benzoquinone

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Abstract
Manganese(IV) complexes Mn(R-R′-sap)2, where H2(R-R′-sap) denotes 2-(salicylideneamino)phenols with the substituent R on the salicylaldehyde ring and the R′ on the o-aminophenol ring, were prepared by the oxidation of binuclear manganese(II) complexes Mn2(R-R′-sap)2 with tetrachloro-o-benzoquinone (TCOQ). The complexes showed magnetic moments corresponding to three unpaired electrons and strong absorptions in the region 15–20×103 cm−1 attributable to CT transitions. Cyclic voltammograms of Mn(R-R′-sap)2 showed two redox waves which can be interpreted in terms of a two-step reaction, Mn(IV)\ightleftharpoonsMn(III)\ightleftharpoonsMn(II). Both redox potentials of the first and the second processes depend on the substituents R and R′, and there is a good correlation between the redox potentials and Hammett’s σ-values of R and R′ to the phenolic oxygen. Mn2(R-R′-sap)2 reacts with TCOQ to give a binuclear manganese(III) complex Mn2(R-R′-sap)2(tcoq), which decomposes in the presence of water forming Mn(R-R′-sap)2.