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

In this work, a series of seven Mn 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), [MnCl(CHNO)] or [MnCl(L1)], (2), bis{μ-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]diethanol}bis[dithiocyanatomanganese(II)], [Mn(NCS)(CHNO)] or [Mn(NCS)(L1)], (3), chlorido{1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}manganese(II) chloride monohydrate, [MnCl(CHNO)(HO)]Cl·HO or [MnCl(L2)(HO)]Cl·HO, (4), {1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}dithiocyanatomanganese(II), [Mn(NCS)(CHNO)] or [Mn(NCS)(L2)], (5), aquadichlorido{2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}manganese(II) 0.3-hydrate, [MnCl(CHNO)(HO)]·0.3HO or [MnCl(L3)(HO)]·0.3HO, (6), (dimethylformamide){2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}dithiocyanatomanganese(II), [Mn(NCS)(CHNO)(CHNO)] or [Mn(NCS)(L3)(DMF)], (7), and (dimethylformamide){2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(butan-1-ol)}dithiocyanatomanganese(II) dimethylformamide monosolvate, [Mn(NCS)(CHNO)(CHNO)]·CHNO or [Mn(NCS)(L4)(DMF)]·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 NO donor set, i.e. three N (pyridine/diimine donors) and two alcohol O atoms, to coordinate the Mn centre. The NO donor set coordinates to the metal centre in a pentagonal planar arrangement; seven-coordinated Mn 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 Mn 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.