Novel dinuclear manganese(III) complexes with bi- or tridentate and bridging tetradentate Schiff base ligands: preparation, properteis and catalase-like function

摘要

Novel mono- and dinuclear manganese(III) complexes: [Mn~(III) (acac)(PA)_2 (I), [Mn~(III) (acac)(N-OPh-sal)(EtOH)] (2),' [Mn_2~(III) (PA)_4(sal-m-xylylene)] (3), [Mn_2~(III)(N-OPh-sal)2(X-sal-m-xylylene)] (X = H (4a), 5-MeO (4b), 3-MeO (4c), 5-Br (4d), and 5-NO_2 (4e) and [Mn_2~(III)(N-OPh-sal)_2(X-salpentn)] (X = H (Sa) and 5-MeO (Sb) have been prepared by ligand substitution reactions and characterized, where Hacac, HPA, N-HOPh-Hsal, H2X-sal-m-xylylene, and H2X-salpentn denote acetylacetone, picolinic acid, N-hydroxyphenyl-salicylideneamine, N,N'-di-substituted-salicylidene-m-xylylenediamine, and N,N'-di-substituted- salicylidene-I,5-pentanediamine, respectively. Single crystals of complexes I, 2, 4a, and Sa were used for X-ray crystallographic determination. Complexes I and 2 have a mononuclear structure, in which the central manganese(l11) ions adopt a distorted ~ octahedral geometry having an elongated axial bond compared to the equatorial bonds due to the Jahn- Teller effect. Forcomplexes 4a and 5a their detailed structures could not be clarified owing to a disorer 0: their ~olecules and quic~ degradation r of the crystals III aIr. However, the results suggested that the two manganese (III) Ions III these complexes are brIdged by one ~ sal-m-xylylene or salpentn ligand to form a dinuclear complex, and each complex has an arrangement similar to that of the tmononuclear complex 2. The reactivities of these manganese(lIl) complexes toward H_2O_2 have been found that the dinuclear . complexes 4a-e, 5a, and Sb can decompose excess amounts of H_2O_2 (H_2O_2/Mn < 100) almost without degradation of the r complexes, whereas complex 3 decomposes with an equimolar amount of H_2O_2. Moreover, the disproportionation rates of H_2O_2 c have been found to depend °~ the bridging tetradentate ligands, the substituents on the phenyl rings of the bridging ligands, and r the solvents used. On the basIs of EPR spectroscopic studies, a series of complexes 4a-e, Sa, and Sb cycle their oxidation levels between Mn_2(III, III) and Mn2(II, II) with dioxygen evolution during the decomposition of H_2O_2.