Synthesis, structure and oxygen-evolving activity of dinuclear manganese complexes with a Schiff-base macrocyclic ligand and bridging benzoate

Abstract

A series of dinuclear manganese complexes [Mn₂L(RCO₂)]ClO₄, where RCO₂H is a substituted benzoic acid and H₂L is a Schiff-base macrocyclic ligand formed by a 2:2 condensation of 2,6-diformyl-4-methylphenol and N,N-bis(2-aminoethyl)methylamine, were synthesized. The crystal structure (R = 2-O₂NC₆H₄–) showed the presence of two crystallographically independent complex cations with slightly different conformations. The difference can be attributed to the crystal packing effect. These complexes catalysed disproportionation of H₂O₂; the activities showed a characteristic V-shaped dependence with pK_a of RCO₂H, which suggests the importance of protonation prior to dissociation of RCO₂^–.