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

Abstract

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{μ-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]diethanol}bis[dithiocyanatomanganese(II)], [Mn₂(NCS)₄(C₁₁H₁₅N₃O₂)₂] or [Mn₂(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·H₂O or [MnCl(L2)(H₂O)]Cl·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)}manganese(II) 0.3-hydrate, [MnCl₂(C₁₅H₂₃N₃O₂)(H₂O)]·0.3H₂O or [MnCl₂(L3)(H₂O)]·0.3H₂O, (6), (dimethylformamide){2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}dithiocyanatomanganese(II), [Mn(NCS)₂(C₁₅H₂₃N₃O₂)(C₃H₇NO)] or [Mn(NCS)₂(L3)(DMF)], (7), and (dimethylformamide){2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(butan-1-ol)}dithiocyanatomanganese(II) dimethylformamide monosolvate, [Mn(NCS)₂(C₁₅H₂₃N₃O₂)(C₃H₇NO)]·C₃H₇NO or [Mn(NCS)₂(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 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 Mn^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 Mn^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.

Keywords: SOD activity; acyclic ligand; catalase mimetic study; crystal structure; manganese; peroxide; superoxide.