Versatile Chelating Behavior of Benzil Bis(thiosemicarbazone) in Zinc, Cadmium, and Nickel Complexes

Reactions of benzil bis(thiosemicarbazone), LH6, with M(NO3)2·nH2O (M = Zn, Cd, and Ni), in the presence of LiOH·H2O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH4] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH6 acts as a N2S2 ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, 1H, and 13C NMR spectroscopies and for the cadmium complex by 113Cd NMR in solution and in the solid state.