Thiodiacetate cobalt(II) complexes: Synthesis, structure and properties

The novel cobalt thiodiacetate complex [Co(tda)(H2O)]n (1a) image was synthesized from the reaction of aqueous solutions of cobalt dichloride with a 1:1 mixture of Na2CO3 and thiodiacetic acid. A second isomer was also obtained occasionally and identified as complex [Co(tda)(H2O)3] (1b). The reaction of 1a with 2,2′-bipyridine (bipy) gave compound [Co(tda)(bipy)(H2O)] · 4H2O (2), which has been structurally characterized and represents, to our knowledge, the first X-ray determination of a thiodiacetate–cobalt complex. The coordination is monomeric pseudo-octahedral as determined by the typical tridentate thiodiacetate ligand with a facial configuration, the chelate bipy ligand and one water molecule. Conversely, the interaction of bis(2-pyridyl)ketone with 1a afforded the compound [Co{OC(OH)(2-pyridyl)2}2]+[Htda]− · 3H2O (3), as confirmed from an X-ray analysis. The bis(2-pyridyl)ketone ligand is hydrolyzed with a concomitant oxidation of the metal to Co(III), a process which has been previously described, while the tda ligand, displaced from the coordination sphere, is monoprotonated and acts as counterion.