Syntheses of phenoxo-bridged Zn(II) and metallamacrocyclic Hg(II) complexes of organochalcogen (Se, Te) substituted Schiff-bases: structure and DNA-binding studies of Zn(II) complexes

Abstract

The coordination of organochalcogen (especially Se and Te) substituted Schiff-bases L1H, L2H, L3H, and L4H toward Zn(II) and Hg(II) has been studied. Reactions of these ligands with ZnCl2 in 1 : 1 molar ratio gave binuclear complexes [{2-[PhX(CH2) n N = C(Ph)]-6-[PhCO]-4-MeC6H2O}2Zn2Cl2] (where X = Se, n = 2 (1); X = Se, n = 3 (2); X = Te, n = 2 (3); and X = Te, n = 3 (4)) with partial hydrolytic cleavage of proligands. In these complexes, two partially hydrolyzed ligand fragments coordinate tridentate (NOO) with two Zn's. Reaction of HgBr2 with L1H and L2H in 1 : 1 molar ratio gave monometallic complexes [C6H2(4-Me)(OH)[2,6-{C(Ph) = N(CH2) n Se(Ph)}2HgBr2]] (n = 2 (5) or 3 (6)) and under similar conditions with L3H and L4H gave bimetallic complexes [C6H2(4-Me)(OH)[2,6-{C(Ph) = N(CH2) n Te(Ph)}2Hg2Br4]] (n = 2 (7) or 3 (8)) in which the ligands coordinate with metal through selenium or tellurium, leaving the imino nitrogen and phenolic oxygen uncoordinated. The proligands L1H, L2H give 14- or 16-membered metallamacrocycles through Se–Hg–Se linkages and L3H, L4H give 16- or 18-membered metallamacrocycles through Te–Hg–Br–Hg–Te linkages. All the complexes were characterized by elemental analyses, ESIMS, FTIR, multinuclear NMR, UV-Vis, and conductance measurements. The redox properties of the complexes were investigated by cyclic voltammetry (CV). Complexes 1–4 exhibited ligand-centered irreversible oxidation processes. Complexes 5 and 6 showed metal-centered quasi-reversible single electron transfer, whereas dinuclear complexes 7 and 8 displayed two quasi-reversible, one-electron transfer steps. A single-crystal X-ray structure determination of 1 showed that the coordination unit is centrosymmetric with Zn(II) in square-pyramidal coordination geometry and the two square pyramids sharing an edge. The Zn ··· Zn separation is 3.232 Å. The DNA-binding properties of 1 and 3 with calf thymus DNA were explored by a spectrophotometric method and CV.