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

• Published in: Journal of coordination chemistry 2012-01, Vol.65 (1), p.28-47
• Main Authors: Asatkar, A.K., Nair, S., Verma, V.K., Verma, C.S., Jain, T.A., Singh, R., Gupta, S.K., Butcher, R.J.
• Format: Article
• Language: English
• Subjects: Calf thymus; Cyclic voltammetry; DNA-binding; Organoselenium/tellurium; Schiff-base; X-ray structure; Zn(II) and Hg(II) complexes
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958972.2011.639874

The coordination of organochalcogen (especially Se and Te) substituted Schiff-bases L 1 H, L 2 H, L 3 H, and L 4 H toward Zn(II) and Hg(II) has been studied. Reactions of these ligands with ZnCl 2 in 1 : 1 molar ratio gave binuclear complexes [{2-[PhX(CH 2 ) n N = C(Ph)]-6-[PhCO]-4-MeC 6 H 2 O} 2 Zn 2 Cl 2 ] (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 HgBr 2 with L 1 H and L 2 H in 1 : 1 molar ratio gave monometallic complexes [C 6 H 2 (4-Me)(OH)[2,6-{C(Ph) = N(CH 2 ) n Se(Ph)} 2 HgBr 2 ]] (n = 2 (5) or 3 (6)) and under similar conditions with L 3 H and L 4 H gave bimetallic complexes [C 6 H 2 (4-Me)(OH)[2,6-{C(Ph) = N(CH 2 ) n Te(Ph)} 2 Hg 2 Br 4 ]] (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 L 1 H, L 2 H give 14- or 16-membered metallamacrocycles through Se-Hg-Se linkages and L 3 H, L 4 H 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.