Trinuclear manganese complexes of unsymmetrical polypodal diamino N 3O3 ligands with an unusual [Mn3(μ-OR) 4]5+ triangular core: Synthesis, characterization, and catalase activity

Abstract

Two new tri-MnIII complexes of general formula [Mn 3L2(μ-OH)(OAc)]ClO4 (H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N′-(2-hydroxybenzyl), N′-(4-X-benzyl)amino]propan-2-ol; 1ClO4, X = Me; 2ClO 4, X = H) have been prepared and characterized. X-ray diffraction analysis of 1ClO4 reveals that the complex cation possesses a Mn 3(μ-alkoxo)2(μ-hydroxo)(μ-phenoxo)4+ core, with the three Mn atoms bound to two fully deprotonated N 3O3 chelating L3-, one exogenous acetato ligand, and one hydroxo bridge, the structure of which is retained upon dissolution in acetonitrile or methanol. The three Mn atoms occupy the vertices of a nearly isosceles triangle (Mn1···Mn3 = 3.6374(12) Å, Mn2···Mn3 3.5583(13) Å, and Mn1···Mn2 3.2400(12) Å), with one substitution-labile site on the apical Mn ion occupied by terminally bound monodentate acetate. Temperature-dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between Mn III ions in 1ClO4. Complexes 1ClO4 and 2ClO4 decompose H2O2 at comparable rates upon initial binding of peroxide through acetate substitution, with retention of core structure during catalysis. Kinetic and spectroscopic studies suggest that these complexes employ the [Mn-(μ-oxo/aquo)-Mn]4+ moiety to activate peroxide, with the additional (μ-alkoxo)(μ-phenoxo)Mn(μ- alkoxo) metallobridge carrying out a structural function.