Di(phenoxo)-bridged Dinuclear Mn2(II,II) and Mn2(II,III) Complexes of Macrocyclic Ligands: Structure, Properties, and Catalase-Like Function

Abstract

Abstract Dinuclear Mn2(II,II) complexes [Mn2(Lm,n)(RCOO)2] ((m,n) = (2,3), (2,4), (3,3); R = CH3, C6H5) have been prepared where (Lm,n)2− denotes dinucleating macrocycles with two 2,6-bis(iminomethyl)-4-methylphenolate entities combined through two lateral chains, –(CH2)m– and –(CH2)n–, at the imino nitrogens. The complex [Mn2(L3,3)(CH3COO)2] crystallizes in the monoclinic space group P21/n with a = 18.795(5), b = 7.608(2), c = 10.081(1) Å, β = 92.89(2)°, V = 1439.7 Å3, and Z = 2. The refinement converges with R = 6.38 and Rw = 9.63% based on 2727 reflections with |Fo| ≥ 3σ(|Fo|). A pair of Mn(II) ions are bridged by the two phenolic oxygens with a Mn–Mn separation of 3.367(1) Å. An acetate group coordinates bidentately to each Mn(II) to afford a six-coordinate geometry about the metal ion. The oxidation of [Mn2(L3,3)(CH3COO)2] with Br2 forms a mixed-valence Mn2(II,III) complex [Mn2(L3,3)(CH3COO)Br2]·H2O. The Mn2(II,II) and Mn2(II,III) complexes show catalytic activity for decomposing H2O2 in DMF or DMSO. The involvement of the Mn2(II,III)/Mn2(II,IV) cycle in the catalytic process is inferred based on visible and ESR spectroscopic studies of the reaction mixture.