title: Dimerization, redox properties and antioxidant activity of two manganese(III) complexes of difluoro- and dichloro-substituted Schiff-base ligands.
abstract: Two mononuclear MnIIIcomplexes [Mn(3,5-F2salpn)(H2O)2][B(C6H5)4]·2H2O (1·2H2O) and [Mn(3,5-Cl2salpn)(OAc)(H2O)]·H2O (2·H2O), where H2salpn=1,3-bis(salicylidenamino)propane, have been prepared and characterized. The crystal structure of 1·H2O shows that this complex forms μ-aqua dimers with a short Mn⋯Mn distance of 4.93Å. Under anaerobic conditions, the two complexes are stable in solution and possess trans-diaxial symmetry with the tetradentate Schiff base ligand symmetrically arranged in the equatorial plane. When left in air, these complexes slowly dimerize to yield high-valent [MnIV2(3,5-X2-salpn)2(μ-O)2] in which each X2-salpn ligand wraps the two Mn ions. This process is favored in basic medium where the deprotonation of the bound water molecule is concomitant with air oxidation. The two complexes catalyze the dismutation of superoxide (superoxide dismutase (SOD) activity) and peroxide (catalase (CAT) activity) in basic medium. The phenyl-ring substituents play an important role on the CAT reaction but have little effect on SOD activity. Kinetics and spectroscopic results indicate that 1 and 2 catalyze H2O2disproportionation through a cycle involving MnIII2and MnIV2dimers, unlike related complexes with a more rigid and smaller chelate ring, which employ MnIII/MnVO monomers.
authors.affiliation: IQUIR (Instituto de Química Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Claudia
authors.initials: C
authors.lastname: Palopoli
authors.affiliation: IQUIR (Instituto de Química Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Gómez
authors.affiliation: Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA, Argentina.
authors.forename: Ana
authors.initials: A
authors.lastname: Foi
authors.affiliation: Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA, Argentina.
authors.forename: Fabio
authors.initials: F
authors.lastname: Doctorovich
authors.affiliation: Institut de Chimie de Toulouse, FR 2599, 118 Route de Narbonne, F-31062 Toulouse, France.
authors.forename: Sonia
authors.initials: S
authors.lastname: Mallet-Ladeira
authors.affiliation: CNRS, LCC (Laboratoire de Chimie de Coordination) and UPS, INPT, LCC, Université de Toulouse, 205 route de Narbonne, F-31077 Toulouse, France.
authors.forename: Christelle
authors.initials: C
authors.lastname: Hureau
authors.affiliation: IQUIR (Instituto de Química Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina. Electronic address: signorella@iquir-conicet.gov.ar.
authors.forename: Sandra
authors.initials: S
authors.lastname: Signorella
mesh_terms: D000975:Antioxidants / Q000138:chemical synthesis / Q000737:chemistry; D002374:Catalase / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry; D006843:Hydrocarbons, Chlorinated / Q000138:chemical synthesis / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000138:chemical synthesis / Q000737:chemistry; D008345:Manganese / Q000737:chemistry*; D012545:Schiff Bases / Q000138:chemical synthesis / Q000737:chemistry; D013482:Superoxide Dismutase / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D056831:Coordination Complexes; D006843:Hydrocarbons, Chlorinated; D006845:Hydrocarbons, Fluorinated; D012545:Schiff Bases; D008345:Manganese; D002374:Catalase; D013482:Superoxide Dismutase
keywords: Dimerization; Kinetics; Mn catalysts; SOD/CAT activity; Structure