Synthesis, characterisation and catalase-like activity of dimanganese(III) complexes of 1,5-bis(5-X-salicylidenamino)pentan-3-ol (X = nitro and chloro)

Abstract

The dimanganese(III,III) complexes [ Mn 2 III ( 5 - NO 2 - salpentO ) ( μ - AcO ) ( μ - MeO ) ( methanol ) 2 ] Y ( 1: Y = Br, 2a: Y = I, 2b: Y = I 3), [ Mn 2 III ( 5 - NO 2 - salpentO ) ( μ - AcO ) ( μ - MeO ) ( methanol ) ( ClO 4 ) ] ( 3) and [ Mn 2 III ( 5 - Cl - salpentO ) ( μ - AcO ) ( μ - MeO ) ( methanol ) 2 ] Br ( 4), where salpentOH is the symmetrical Schiff base ligand 1,5-bis(salicylidenamino)pentan-3-ol, were synthesised and structurally characterized. Complex 2b crystallises in the monoclinic system, space group P2 1/c, and exhibits Mn⋯Mn separation of 2.911 Å. This Mn⋯Mn separation is very close to the other characterized ( μ - alkoxo ) 2 ( μ - acetato ) Mn 2 III complexes of X-salpentOH (X = MeO, Br and H) and reveals that the aromatic substituent has little influence on the geometric parameters of the bimetallic core. A correlation between the electronic character of the different ring substituents, the redox potentials of the dinuclear complexes and their catalase activity was evidenced. Complexes 1– 4 show saturation kinetics with [H 2O 2] and the H 2O 2 disproportionation involves redox cycling between the Mn 2 III / Mn 2 IV levels. The catalytic activity studies show that bound acetate is required for catalase activity and that the acetato and alkoxo bridges serve as internal bases facilitating the proton transfer coupled to oxidation of the metal centre.