Synthesis and Crystal Structure of a Novel Binucleating Symmetrical μ-Bis(tetradentate) Schiff Base Ligand: Syntheses and Redox Properties of Dimanganese(III/III) Complexes

Abstract

A family of dinuclear manganese(III/III) complexes [Mn2III(μ-X)(μ-L)(Y)2](Z)2 (X = Cl, OMe, OEt; Y = H2O; Z = Cl) (6a−c) of a new μ-bis(tetradentate) ligand, H3L, derived from the stepwise Schiff base condensation of triethylenetetramine, acetylacetone, and salicylaldehyde has been reported for the first time. NMR spectral and single crystal X-ray structural characterizations of the ligand confirm the formation of a five-membered imidazolidine ring as a backbone to have a new type of doubly bridging binucleating ligand system. In methanol solutions both the MnIIIMnIV/MnIIIMnIII and MnIIIMnIII/MnIIIMnII couples are observable for the chloro-bridged complex with E1/2 in the range of +0.49 to −0.13 V vs. saturated calomel electrode (SCE). The calculation of the comproportionation constant (Kc) from the E1/2 values clearly point towards the role of the Mn−O(phenolate)−Mn core for thermodynamic stability of the parent dimanganese(III/III) complex.