Synthesis and crystal structure of a novel binucleating symmetrical mu-bis(tetradentate) Schiff base ligand: Syntheses and redox properties of dimanganese(III/III) complexes

A family of dinuclear manganese (III/III) complexes [Mn-2(III)(mu -X) (mu - L)(Y)(2)](Z)(2) (X = Cl, OMe, OEt; Y = H2O; Z = Cl) (6a-c) of a new mu -bis (tetradentate) ligand, H3L, derived from the stepwise Schiff base condensat ion of triethylenetetramine, acetylacetone, and salicylaldehyde has been re ported for the first time. NMR spectral and single crystal X-ray structural characterizations of the ligand confirm the formation of a five-membered i midazolidine ring as a backbone to have a new type of doubly bridging binuc leating ligand system. In methanol solutions both the (MnMnIV)-Mn-III/Mn(II I)Mn(III)and (MnMnIII)-Mn-III/(MnMnII)-Mn-III couples are observable for th e chloro-bridged complex with E-1/2 in the range of +0.49 to -0.13 V vs, sa turated calomel electrode (SCE). The calculation of the comproportionation constant (K-e) from the E1/2 values clearly point towards the role of the M n-O(phenolate)-Mn core for thermodynamic stability of the parent dimanganes e(III/III) complex.