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

Insights into Second-Sphere effects on redox potentials, spectroscopic properties, and superoxide dismutase activity of manganese complexes with Schiff-Base Ligands

Six Mn-Schiff base complexes, [Mn(X-salpn)]0/+ (salpn = 1,3-bis(sal-ic-ylidenamino)propane, X = H [1], 5-Cl [2], 2,5-F2 [3], 3,5- Cl2 [4], 5-NO2 [5], 3,5-(NO2)2 [6]), were synthesized and characterized in solution, and second-sphere effects on their electrochemical and spectroscopic properties were analyzed. The six complexes catalyze the dismutation of superoxide with catalytic rate constants in the range 0.65 to 1.54 × 106 M−1 s −1 obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutases assay, in aqueous medium of pH 7.8. In solution, these compounds possess two labile solvent molecules in the axial positions favoring coordination of the highly nucleophilic O2 •− to the metal center. Even complex 5, [Mn(5- (NO2)salpn) (OAc) (H2O)], with an axial acetate in the solid state, behaves as a 1:1 electrolyte in methanolic solution. Electron paramagnetic resonance and UV−vis monitoring of the reaction of [Mn(X-salpn)]0/+ with KO2 demonstrates that in diluted solutions these complexes behave as catalysts supporting several additions of excess O2 •−, but at high complex concentrations (≥0.75 mM) catalyst self-inhibition occurs by the formation of a catalytically inactive dimer. The correlation of spectroscopic, electrochemical, and kinetics data suggest that second-sphere effects control the oxidation states of Mn involved in the O2 •− dismutation cycle catalyzed by complexes 1−6 and modulate the strength of the Mn-substrate adduct for electron-transfer through an inner-sphere mechanism.Fil: Palopoli, Claudia. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario (IQUIR -CONICET); Argentina.Fil: Ferreyra, Joaquín. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario (IQUIR -CONICET); Argentina.Fil: Conte-Daban, Amandine. Université de Toulouse. Laboratoire de Chimie de Coordination (LCC-CNRS); France.Fil: Foi, Ana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y ́ Naturales. Departamento de Química Inorgánica, Analítica y Química Física. Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE -CONICET); Argentina.Fil: Doctorovich, Fabio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y ́ Naturales. Departamento de Química Inorgánica, Analítica y Química Física. Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE -CONICET); Argentina.Fil: Anxolabehére-Mallart, Elodie. Université Paris-Diderot. Laboratoire d'Electrochimie Moleculaire (LEM - CNRS); France.Fil: Hureau, Christelle. Université de Toulouse. Laboratoire de Chimie de Coordination (LCC-CNRS); France.Fil: Signorella, Sandra R. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario (IQUIR -CONICET); Argentina