The first example of a reversibly reducible CoII complex with an anionic 2-thiohydantoin-type ligand

The reaction of the potassium salt of 3-phenyl-5(Z)-(pyridin-2-ylmethylene)-2-thioxoimidazolidin-4-one (KL) with CoCl₂·6H₂O in MeCN results in formation of the neutral complex Co^IIL₂. According to single-crystal X-ray analysis, the Co^II centre is coordinated to four nitrogen atoms of two organic ligands and has a distorted tetrahedral geometry. This complex undergoes electrochemical reduction with consequent two reversible and one quasi-reversible stages.