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

The novel cobalt thiodiacetate complex [Co(tda)(H2O)](n), (1a) (tda = S(CH2COO)(2)(2-)) 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)] • 4H(2)O (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 thiodiacerate ligand with a facial configuration, the chelate bipy ligand and one water molecule. Conversely, the interaction of bis(2-pyridyl)ketone with la afforded the compound [Co{OC(OH)(2-pyridyl)(2)}(2)](+)[Htda](-) • 3H(2)O (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.