NNS tridentate thiosemicarbazide and 1,3,4-thiadiazole-2-amine complexes of some transition metal ions: syntheses, structure and fluorescence properties

<p>The reactions of Zn(II), Mn(II), and Ni(II) acetates with 1-picolinoyl-4-phenyl-3-thiosemicarbazide (Hppts) yielded [Zn(ppts)₂]·CHCl₃ (<b>3</b>), [Mn(ppts)₂]·THF (<b>4</b>), and [Ni(ppts)₂]·THF (<b>5</b>), respectively, but HgCl₂ gave a cyclized product N-phenyl-5-(pyridin-2-yl)-1,3,4-oxadiazole-2-yl-amine (<b>2</b>). The treatment of Hppts with conc. H₂SO₄ formed N-phenyl-5-(pyridin-2-yl)-1,3,4-thiadiazole-2-yl-amine (<b>1</b>). Hppts is a nonfluorescent material, but <b>3</b>, <b>4</b> and the cyclized products 1,3,4-oxadiazole/1,3,4-thiadiazole are fluorescent. The cyclized ligand N-phenyl-5-(pyridin-2-yl)-1,3,4-thiadiazole-2-amine (<b>1</b>) formed [Zn(2-Hppt)₂(OAc)₂] (<b>6</b>) and [Cd₂(2-Hppt)₂(OAc)₂(<i>μ</i>-OAc)₂] (<b>7</b>) in which Cd(II) has a binuclear acetate-bridged seven coordinate pentagonal bipyramidal geometry. Complex <b>7</b> is also a fluorescent material with maximum emission at 425 nm at an excitation wavelength of 254 nm.