Manganese(II) complexes derived from acyclic ligands having flexibie alcohol arms: structural chracterization and SOD and catalase mimetic studies

In this work, a series of seven Mn-II complexes of noncyclic flexible ligands derived from 2,6-diformylpyridine and ethanolamine or alkyl-substituted ethanolamines were prepared and characterized, six structurally by single-crystal X-ray diffraction studies. The complexes are dichlorido{2,2'-[pyridine-2,6-diyl)- bis (nitrilomethanylylidene)] diethanol}manganese(II) [MnCl2(C11H15N3O2)] or [MnCl2(L1)], (2), bis{mu -2,2'-[(pyridine-2,6-diyl)bis (nitrilomethanylylidene)] di-ethanol}bis[dithiocyanatomanganese(II)], [Mn-2(NCS)(4)(C11H15N3O2)(2)] or [Mn-2-(NCS)(4)(L1)(2)], (3), chlorido{1,1'(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]-bis(propan-2-ol)}manganese (II) chloride monohydrate, [MnCl(C13H19N3O2)-(H2O)]Cl center dot H2O or [MnCl(L2)(H2O)]Cl center dot H2O, (4), {1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}dithiocyanatomanganese(II), [Mn-(NCS)(2)(C13H19N3O2)] or [Mn(NCS)(2)(L2)], (5), aquadichlorido{2,2' -dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)Imanganese(II) 0.3-hydrate, [MnCl2(C15H23N3O2)(H2O)]center dot-0.3H(2)O or [MnCl2(L3)(H2O)]center dot -0.3H(2)O, (6), (climethylformamide){2,2'-dimethyl-2,2'[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}dithiocyanatomanganese(H), [Mn(NCS)(2)(C15H23N3O2)(C3H7NO)] or [Mn(NCS)(2)(L3)(DMF)], (7), and (dimethylformamide)-{2,2[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(butan-l-ol)}dithiocyan-atomanganese(II) dimethylformamide monosolvate, [Mn(NCS)(2)(C15H23N3O2)-(C3H7NO)]center dot C3H7NO or [Mn(NCS)(2) (L4)(DMF)]center dot DMF, (8). The crystal structure of ligand L1 is also reported, but that of (5) is not. All four ligands (L1-L4) have five potential donor atoms in an N3O2 donor set, i.e. three N (pyridine/diimine donors) and two alcohol O atoms, to coordinate the Mn-II centre. The N3O2 donor set coordinates to the metal centre in a pentagonal planar arrangement; seven-coordinated M-II complexes were obtained via coordination of two auxiliary ligands (anions or water molecules) at the axial positions. However, in some cases, the alcohol O-atom donors remain uncoordinated, resulting in five- or six-coordinated M-II complexes. The structurally characterized complexes were tested for their catalytic scavenging of superoxide and peroxide. The results indicated that the complexes with coordinated exogenous water or chloride ligands showed higher SOD activity than those with exogenous thiocyanate ligands.

Automated summary

A series of Mn-II complexes were synthesized and characterized in this work, with six of them structurally analyzed by single-crystal X-ray diffraction studies. The complexes exhibit different coordination modes and binding patterns of ligands, affecting their scavenging activity towards superoxide and peroxide. Coordination of exogenous water or chloride ligands in the complexes resulted in higher superoxide dismutase activity compared to those with thiocyanate ligands.