Variability in the Coordination Modes of 2-Pyridineformamide Thiosemicarbazone (HAm4DH) in some Zinc(II), Cadmium(II), and Mercury(II) Complexes



The reduction of 2-cyanopyridine by sodium in dry methanol in the presence of thiosemicarbazide produces 2-pyridineformamide thiosemicarbazone, HAm4DH. The reactions of the potentially tridentate ligand HAm4DH with salts of Zn, Cd, and Hg gave a variety of metal-ligand complexes. The complexes were characterized by mass spectrometry as well as IR and multinuclear NMR (1H, 13C, 13C CP/MAS, 113Cd, 199Hg) spectroscopy. The crystal structures of [Zn(Am4DH)(OAc)]2·H2O, [Hg(HAm4DH)2Br2]·C2H5OH and equation image[Hg(μ-S-Am4DH)Br] were obtained. Coordination of anionic Am4DH occurs through the pyridyl nitrogen, imine nitrogen and thiolato sulfur atoms, while the neutral ligands in [Hg(HAm4DH)2Br2] coordinate as monodentate ligands through their thione sulfur atoms. One of the acetate ligands in [Zn(Am4DH)(OAc)]2·H2O is bridging monodentate and the other bridging bidentate. equation image[Hg(μ-S-Am4DH)Br] features five-coordinate mercury centers with bridging thiolato sulfur atoms. The intermolecular arrangement is dictated by hydrogen bonding from the amino groups and by π-π stacking of the pyridine rings.