Mono-, di- and tri-nuclear manganese(II) complexes derived from a quinquedentate ligand: Superoxide dismutase and catalase mimetic studies

•A pentadentate Schiff base ligand and its mono and trinuclear Mn(II) complexes were synthesized.•Mn2Ca complex of the ligand was also synthesised.•Solid state structures of the complexes were determined by single crystal X-ray diffraction study.•Superoxide dismutase and catalase activities of the complexes were evaluated.

In this study, three manganese complexes [Mn(H2L)Cl2]·MeOH, [Mn3(L)2(OAc)2(MeOH)2]·2MeOH and [Mn2Ca(L)2(OAc)2(MeOH)2]·2MeOH derived from a quinquedentate Schiff base ligand (H2L) were synthesised and characterised by the spectroscopic and analytic methods. Molecular structures of the complexes were determined by single crystal X-ray diffraction studies. In mononuclear complex [Mn(H2L)Cl2]·MeOH, the Mn(II) ions are seven-coordinate pentagonal bipyramidal geometry with two chloride ions at the axial positions. The trinuclear complex [Mn3(L)2(OAc)2(MeOH)2]·2MeOH consists of two mononuclear units linked by a central Mn(II) ion. The calcium containing complex [Mn2Ca(L)2(OAc)2(MeOH)2]·2MeOH contains two mononuclear units bridged by a six-coordinate Ca(II) ion. The superoxide dismutase (SOD activities of the structurally complexes were evaluated and the mononuclear complex [Mn(H2L)Cl2]·MeOH showed the greatest SOD activity with an IC50 value of 0.95 μM which gives a calculated kcat value of 1.67 × 106 M−1 s−1. Finally, the ability of the complexes to disproportionate H2O2 in the presence of base was tested by measuring the rate of oxygen evolution at room temperature. The trinuclear [Mn3(L)2(OAc)2(MeOH)2]·2MeOH complex is the most efficient complex catalase mimic of the tested complexes with the fastest rate 5.33 ml/s.

Graphical abstractIn this study, a Schiff base ligand and its mono, di- and trinuclear Mn(II) complexes were prepared and characterised by spectroscopic and analytical methods. Molecular structures of the complexes were determined by single crystal X-ray diffraction study. Additionally, SOD and catalase activities for the complexes were investigated.Figure optionsDownload full-size imageDownload as PowerPoint slide