Synthesis, structural characterization, electrochemical studies and DFT calculations on nickel(II) complexes of N-picolinoyl-N′-benzothioylhydrazide and 5-(pyridine-4-yl)-2H-1,2,4-triazole-3-thione

Abstract

Two Ni(II) complexes, [Ni(pbth)2] and [Ni(ptt)2(en)2] {Hpbth = N-picolinoyl-N′-benzothioylhydrazide, Hptt = 5-(pyridine-4-yl)-2H-1,2,4-triazole-3-thione} have been synthesized and characterized by physico-chemical and spectroscopic methods. [Ni(pbth)2] contains a pair of N-picolinoyl-N′-benzothioylhydrazide ligands coordinated via their thione sulfur, pyridyl nitrogen and hydrazinic nitrogen atoms, forming two C2N2Ni and two CSN2Ni five-membered chelate rings. The intermediate compound 1-isonicotinoyl-3-thiosemicarbazide is converted to 5-(pyridine-4-yl)-2H-1,2,4-triazole-3-thione in the presence of ethanolic NaOH, giving the complex [Ni(ptt)2(en)2] in which the ptt ligands coordinate through their triazole ring nitrogen atoms, while four more nitrogens from two ethylenediamine ligands complete the octahedral structure. The crystal structures of the complexes involve various types of intermolecular extended hydrogen bonds, forming supramolecular frameworks. Cyclic voltammetry studies of both complexes show quasi-reversible redox behavior. Density Functional Theory electronic structure calculations corroborate our experimental findings.