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

The crystal structures Of [M-2(phen)(4)(H2O)(2)(C4O4)](.) C4O4. 8H(2)O [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 [Co-2(phen)(4)(H2O)(2)(C4O4)](2+) (1) and [Mn-2(phen)(4)(H2O)(2)(C4O4)](2+) (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C4O42-(SQ(2-)) dianion and crystalization water molecules. In both complexes the metal ions have distorted octahedral geometry. The squarate adopts the u- 1,3 (1) and (2) bis(monodentate) coordination modes, the intradimer M-M separation being 8.053(7) angstrom (1) and 8.175(4) angstrom (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 SQ(2-) is oxidized in two consecutive steps to the corresponding radical mono-anion and neutral