Hg(II) complexes of 4-phenyl-5-(3-pyridyl)-1,2,4-triazole-3-thione and 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione and a Ni(II) complex of 5-(thiophen-2-yl)-1,3,4-oxadiazole-2-thione: Synthesis and X-ray structural studies

Three new mixed ligand complexes, [Hg(en)(4-pptt)2] (2) {4-pptt = 4-phenyl-5(3-pyridyl)-1,2,4-triazole-3-thione}, [Hg(en)(4-pot)2] (3) {4-pot = 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione} and [Ni(en)2(5-thot)2] (4) {5-thot = 5-(thiophen-2-yl)-1,3,4-oxadiazole-2-thione}, have been prepared containing en as a co-ligand. It is observed that 5-(pyridine-4-carbonyl) hydrazine carbodithioic acid methyl ester undergoes cyclization during complexation with Hg(II) in the presence of ethylenediamine and formed complex 3 containing 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione. The metal complexes have been characterized with the aid of elemental analyses, IR, magnetic susceptibility and single crystal X-ray studies. The ligand 4-pptt (1) and complexes 2, 3 and 4 crystallize in the monoclinic system, space group P21/n, P21/c, P121/c1 and P21/n respectively. The ligand is present in the deprotonated thiol form in complexes 2 and 3, and is bonded covalently through sulfur, while in complex 4 the ligand 5-(thiophen-2-yl)-1,3,4-oxadiazole-2-thione is present as the thione form and is bonded to Ni(II) through the oxadiazole nitrogen. Complex 4 shows quasi-reversible redox behavior assignable to a Ni2+/Ni3+ one electron transfer. The photoluminescence properties indicate that the complexes are fluorescent materials with maximum emissions at 433, 376 and 465 nm for complexes 2, 3 and 4 at excitation wavelengths of 293, 273 and 327 nm, respectively. All the complexes contain extended hydrogen bonding that provides a supramolecular framework.

Graphical abstractNew mixed ligand complexes [Hg(en)(4-pptt)2] (2), [Hg(en)(4-pot)2] (3) and [Ni(en)2(5-thot)2] (4) have been reported, containing en as a co-ligand. It is observed that 5-(pyridine-4-carbonyl) hydrazine carbodithioic acid methyl ester underwent cyclization during complexation with Hg(II) in the presence of ethylenediamine and formed complex 3 containing 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione. The ligand is present in the deprotonated thiol form in complexes 2 and 3 and is bonded covalently through sulfur, while in complex 4 the ligand 5-(thiophen-2-yl)-1,3,4-oxadiazole-2-thione is present in the thione form and is bonded to Ni(II) through the oxadiazole nitrogen. The photoluminescence properties indicate that the complexes are fluorescent materials with maximum emissions at 433, 376 and 465 nm for complexes 2, 3 and 4 at an excitation wavelength of 293, 273 and 327 nm, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide