Zinc(II) complexes of 1,3-bis(2-pyridylmethylthio)propane: Anion dependency, crystal structure and DNA binding study

Zinc(II) complexes of the formula [Zn(L)(X)2] (where X = Cl−, N3−, NCO− and SCN− (1a–d, respectively)) and {[Zn(L)(ClO4)(H2O)](ClO4)}n (2), were isolated in the pure form on the reaction of 1,3-bis(2-pyridylmethylthio)propane (L) with different zinc(II) salts. All the complexes were characterized by physicochemical and spectroscopic tools. The X-ray crystallographic analyses of the complexes 1d and 2 showed that the former is mononuclear while complex 2 is a 1D coordination polymer, {[Zn(L)(ClO4)(H2O)](ClO4)}n, due to a different coordination mode of the tetradentate ligand L. The zinc(II) ions present an octahedral coordination geometry in both compounds, which is more distorted in the mononuclear complex 1d. The study indicates that the counter anion of the zinc(II) salt used as reactant leads to a different type of complex when isolated as a crystalline material. A spectroscopic study of the interaction of complex, 2 with calf thymus-DNA (CT-DNA) in Tris–HCl buffer showed a significant non-intercalative interaction with a binding constant (Kb) of 4.7 × 104 M−1, and the linear Stern–Volmer quenching constant (Ksv) and the binding sites (n) were found to be 1.3 × 103 and 0.92 respectively, calculated from ethidium bromide (EB) fluorescence displacement experiments.

On reaction of 1,3-bis(2-pyridylmethylthio)propane (L) with different zinc(II) salts different types of zinc(II) complexes of the formula [Zn(L)(X)2] (where X = Cl−, N3−, NCO− and SCN− (1a–d, respectively)) and {[Zn(L)(ClO4)(H2O)](ClO4)}n (2) were obtained and characterized by physicochemical and spectroscopic tools. The X-ray crystallographic analyses of the complexes showed that 1d is mononuclear while complex 2 is a 1D coordination polymer. The counter anion of the zinc(II) salt used as the reactant led to the formation of different types of complexes. The interaction of the polymeric complex 2 with calf thymus-DNA (CT-DNA) in Tris–HCl buffer has been studied spectroscopically.Figure optionsDownload as PowerPoint slideHighlights
► The reaction of L and zinc(II) acetate gave four [Zn(L)(X)2] complexes (X = Cl−, N3−, NCO− and SCN−).
► On reaction of L with zinc(II) perchlorate, {[Zn(L)(ClO4)(H2O)](ClO4)}n (2) was obtained.
► No significant result was observed taking zinc(II) nitrate or zinc(II) chloride as the reactant.
► The spectral titration with CT-DNA showed a significant non-intercalative behavior of 2.
► Ethidium bromide-fluorescence displacement experiments suggests the groove binding mode of 2.