Copper(II) complex of in situ formed 5-(2-pyridyl)-1,3,4-triazole through C–S bond cleavage in 1,2-bis(2-pyridylmethylthio)-bis-ethylsulphide: Synthesis, structural characterization and DNA binding study

On reaction of 1,2-bis(2-pyridylmethylthio)-bis-ethylsulphide (L) with copper(II) chloride in presence of an excess of azide ions led to the formation of a new copper(II) complex formulated as [Cu(2-PTrz)2(H2O)2] (1), where 2-PTrz = 5-(2-pyridyl)-1,3,4-triazole is formed through the cleavage of C–S bond in L promoted by copper(II) chloride. The precursor of 1 is the in situ formed Cu(pic)2 derivative (pic = 2-picolinate), the existence of which has been established by separating out in pure form the complexes [Cu2(pic)3(H2O)](ClO4) (2), [Cu2(pic)3(H2O](NO3) (3) by using different anions. In addition [Cu(pyca)Cl] (4) (pyca = bis(pyridin-2-carbonyl)amine) was also obtained from 1 with a less quantity of azide. All the copper(II) complexes obtained in this study were characterized by physico-chemical tools as well as X-ray crystallographic studies. The 2-PTrz ligand separated out from 1 was used in the synthesis of the nickel(II) complex [Ni(2-PTrz)2(H2O)2], 5. The complexes 1 and 5 are isomorphous and isostructural. In dimethylformamide solution, complex 1 was found to exhibit CuII/CuI quasi-reversible redox couple in cyclic voltammograms with E1/2 value of −340 mV (versus Ag/AgCl) at 298 K. The interaction of complex 1 with CT-DNA has been investigated spectroscopically. The results showed that the interaction mode between complex 1 and DNA might be groove binding.