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-pyridine-formamide 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 (H-1, C-13, C-13 CP/MAS, Cd-113, Hg-199) spectroscopy. The crystal structures of [Zn(Am4DH)(OAc)](2)-H2O, [Hg(HAm4DH)(2)Br-2](C2H5OH)-C-. and (1)(infinity)[Hg(mu-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)(2)Br-2] coordinate as monodentate ligands through their thione sulfur atoms. One of the acetate ligands in [Zn(Am4DH)(OAc)](2)(H2O)-H-. is bridging monodentate and the other bridging bidentate. (1)(infinity)[Hg(mu-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 pi-pi stacking of the pyridine rings.