Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

Abstract

The crystal structures of [M2(phen)4(H2O)2(C4O4)]· C4O4· 8H2O [M = Co2+ (1), Mn2+ (2); phen: 1,10-phenanthroline] complexes have been prepared and characterized by IR spectroscopy, thermal analysis and single X-ray diffraction techniques. Their structures consist of [Co2(phen)4(H2O)2(C4O4)]2+ (1) and [Mn2(phen)4(H2O)2(C4O4)]2+ (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C4O 4 2− (SQ2−) dianion and crystalization water molecules. In both complexes the metal ions have distorted octahedral geometry. The squarate adopts the μ-1,3 (1) and (2) bis(monodentate) coordination modes, the intradimer M–M separation being 8.053(7) A (1) and 8.175(4) A (2), respectively, while the other squarate acts as a counter anion. The voltammetric behaviour of complexes (1) and (2) was investigated in DMSO (dimethylsulfoxide) solution by cyclic voltammetry using n-Bu4NClO4 as supporting electrolyte. The complexes exhibit both metal and ligand centred electroactivity in the potential ±1.75 V versus Ag/AgCl reference electrode. The dianion SQ2− is oxidized in two consecutive steps to the corresponding radical monoanion and neutral form.