Dinuclear Cobalt and Manganese Squarate Complexes with Bidentate N-Donor Ligand: Syntheses, Crystal Structures, Spectroscopic, Thermal and Voltammetric Studies

Abstract

The crystal structures of [M<inf>2</inf>(phen)<inf>4</inf>(H <inf>2</inf>O)<inf>2</inf>(C<inf>4</inf>O<inf>4</inf>)]• C <inf>4</inf>O<inf>4</inf>• 8H<inf>2</inf>O [M =Co2+ (1), Mn 2+ (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<inf>2</inf>(phen)<inf>4</inf>(H <inf>2</inf>O)<inf>2</inf>(C<inf>4</inf>O<inf>4</inf>)]2+ (1) and [Mn<inf>2</inf>(phen)<inf>4</inf>(H<inf>2</inf>O)<inf>2</inf>(C <inf>4</inf>O<inf>4</inf>)]2+ (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C<inf>4</inf>O <inf>4</inf> 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) Å (1) and 8.175(4) Å (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-Bu<inf>4</inf>NClO<inf>4</inf> 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. © Springer 2006.