Coordination behavior of 3,4-bis(2-pyridylmethylthio)toluene with copper(II) ions: Synthesis, structural characterization and reactivity, and DNA binding study of the dinuclear copper(II) complex

On reaction of different copper(II) salts with 3,4-bis(2-pyridylmethylthio)toluene (L) having neutral tetradentate NSSN donor set in different chemical environments, two mononuclear copper(II), one dinuclear copper(I) and one dinuclear copper(II) complexes, formulated as [CuII(L)(H2O)2](NO3)2 (1), [CuII(pic)2] (2), [CuI2(L)2](ClO4)2 (3) and [CuII2(L)2Cl2](ClO4)2 (4), respectively, were isolated in pure form [where pic = picolinate]. All the complexes were characterized by physicochemical and spectroscopic methods. The product of the reactions are dependent on the counter anion of copper(II) salts used as reactant and on the reaction medium. Complexes 1 and 4 were obtained with nitrate and perchlorate copper(II) salts, respectively. On the other hand, C–S bond cleavage was observed in the reaction of L with copper(II) chloride to form in situ picolinic acid and complex 2. Dinuclear complexes 3 and 4 were separated out when copper(II) perchlorate was allowed to react with L in methanol and in acetonitrile, respectively, under aerobic condition. The X-ray diffraction analysis of the dinuclear complex 3 shows a highly distorted tetrahedral geometry about each copper ion. Complex 4 is converted to 3 in acetonitrile in presence of catechol. The spectral study of complex 4 with calf thymus DNA is indicative of a groove binding mode interaction.

The coordination behavior of a newly designed tetradentate N2S2 ligand 3,4-bis(2-pyridylmethylthio)toluene (L) towards different copper(II) salts has been studied. The resulting complexes are dependent on the counter anion of copper(II) salts used as reactant and on the reaction medium. Copper(II) perchlorate leads to the formation of a dinuclear copper(II) complex in acetonitrile but dinuclear copper(I) complex in methanol showing the reducing behavior of the solvent. In methanol it was observed the slowly conversion of the dinuclear copper(II) species to copper(I), whereas the process proceeds faster in acetonitrile in presence of catechol.Figure optionsDownload as PowerPoint slide