Trinuclear Manganese Complexes of Unsymmetrical Polypodal Diamino N₃O₃ Ligands with an Unusual [Mn₃(μ-OR)₄]⁵⁺ Triangular Core: Synthesis, Characterization, and Catalase Activity

Two new tri-Mn^III complexes of general formula [Mn₃L₂(μ-OH)­(OAc)]­ClO₄ (H₃L = 1-[<i>N</i>-(2-pyridylmethyl),<i>N</i>-(2-hydroxybenzyl)­amino]-3-[<i>N</i>′-(2-hydroxybenzyl),<i>N</i>′-(4-X-benzyl)­amino]­propan-2-ol; <b>1</b>ClO₄, X = Me; <b>2</b>ClO₄, X = H) have been prepared and characterized. X-ray diffraction analysis of <b>1</b>ClO₄ reveals that the complex cation possesses a Mn₃(μ-alkoxo)₂(μ-hydroxo)­(μ-phenoxo)⁴⁺ core, with the three Mn atoms bound to two fully deprotonated N₃O₃ chelating L^3–, 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 <b>1</b>ClO₄. Complexes <b>1</b>ClO₄ and <b>2</b>ClO₄ 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