RESUMO
Two mononuclear MnIII complexes [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 Mnâ¯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 H2O2 disproportionation through a cycle involving MnIII2 and MnIV2 dimers, unlike related complexes with a more rigid and smaller chelate ring, which employ MnIII/MnVO monomers.
Assuntos
Antioxidantes , Catalase/química , Complexos de Coordenação , Hidrocarbonetos Clorados , Hidrocarbonetos Fluorados , Manganês/química , Superóxido Dismutase/química , Antioxidantes/síntese química , Antioxidantes/química , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Hidrocarbonetos Clorados/síntese química , Hidrocarbonetos Clorados/química , Hidrocarbonetos Fluorados/síntese química , Hidrocarbonetos Fluorados/química , Bases de Schiff/síntese química , Bases de Schiff/químicaRESUMO
Two imidazolate-bridged diCuII and CuIIZnII complexes, [CuZn(dien)2(µ-Im)](ClO4)3·MeOH (1) and [Cu2(dien)2(µ-Im)](ClO4)3 (2) (Im = imidazole, dien=diethylenetriamine), and two complexes formed with Schiff base ligands, [CuZn(salpn)Cl2] (3) and [Cu2(salbutO)ClO4] (4) (H2salpn=1,3-bis(salicylidenamino)propane, H3salbutO=1,4-bis(salicylidenamino)butan-2-ol) have been prepared and characterized. The reaction of [Cu(dien)(ImH)](ClO4)2 with [Zn(dien)(H2O)](ClO4)2 at pH≥11 yields complex 1; at lower pH, the Cu3Zn tetranuclear complex [{(dien)Cu(µ-Im)}3Zn(OH2)(ClO4)2](ClO4)3 (1a) forms as the main reaction product. X-ray diffraction of 1a reveals that the complex contains a metal centered windmill-shaped cation having three blades with a central Zn ion and three peripheral capping Cu(dien) moieties bound to the central Zn ion through three imidazolate bridges. The four complexes are able to disproportionate O2- in aqueous medium at pH7.8, with relative rates 4>1>2â«3. [Cu2(salbutO)]+ (4) is the most easily reducible of the four complexes and exhibits the highest activity among the SOD models reported so far; a fact related to the ligand flexibility to accommodate the copper ion in both CuI and CuII oxidation states and the lability of the fourth coordination position of copper facilitating stereochemical rearrangements.
Assuntos
Cobre/química , Imidazóis/química , Modelos Químicos , Superóxido Dismutase/química , Superóxidos/química , Oxirredução , Bases de Schiff/químicaRESUMO
Two new tri-Mn(III) complexes of general formula [Mn3L2(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; 2ClO4, X = H) have been prepared and characterized. X-ray diffraction analysis of 1ClO4 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 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.