Structural diversity in copper(II) complexes of bis(thiosemicarbazone) and bis(semicarbazone) ligands

Abstract

Two symmetrical bis(carbazone) ligands, H4L1 and H4L2, were prepared by condensation of 4,6-diacetylresorcinol with thiosemicarbazide and semicarbazide, respectively. Their structures were elucidated by elemental analyses and IR, electronic and 1H NMR spectroscopy. Both ligands are tetrabasic and contain two sets of SNO (H4L1) or ONO (H4L2) coordinating sites. Binuclear, trinuclear and dimeric CuII complexes and also adducts with organic bases were prepared. Reactions of H4L1 with several CuII salts, including Cl−, AcO−, , and , in addition to CuI as CuI, afforded different binuclear complexes depending on the salt and the working conditions, except for CuCl2, where a trinuclear complex with a unique mode of bonding was obtained. These complexes reflect the strong coordinating power of Cl−, and AcO− compared to . The mode of bonding and the basicity of the H4L1 ligand are also influenced by the counteranion, the pH of the reaction medium, the working conditions and the oxidation state of copper. The reactivity of the binuclear CuII complexes of both H4L1 and H4L2 towards 1,10-phenanthroline (Phen), 2,2′-bipyridyl (Bpy), N,N,N′,N′-tetramethylethylenediamine (Tmen) and 8-hydroxyquinoline (Oxine; Ox) were investigated. Adducts with organic bases were obtained in the mole ratio 2 : 1 : 1 for H4L1 and 2 : 1 : 2 for H4L2 [CuII : ligand : base (base = Phen, Bpy or Ox)], which reflects the difference in size of S and O. With Tmen, dimeric complexes were obtained containing no Tmen molecules instead of the expected adducts for both H4L1 and H4L2. Evidently the presence of Tmen in the reaction mixture enhances the dimerization process. Characterization and structure elucidation of the complexes was achieved by elemental and thermal analyses, electronic, IR, mass and ESR spectroscopy, as well as conductance and magnetic susceptibility measurements. Finally, the antifungal and antibacterial activities of H4L1 and its metal complexes were investigated.