Mixed-ligand nickel(II) thiosemicarbazone complexes: Synthesis, characterization and biological evaluation

The syntheses and characterization of some new mixed-ligand nickel(II) complexes {[Ni(L1)(PPh3)] (1), [Ni(L1)(Py)] (2), [Ni(L2)(PPh3)]·DMSO (3), [Ni(L2)(Imz)] (4), [Ni(L3)(4-pic)] (5) and [{Ni(L3)}2(μ-4,4′-byp)]·2DMSO (6)} of three selected thiosemicarbazones {the 4-(p-X-phenyl)thiosemicarbazones of salicylaldehyde} (H2L1−3) (A, Scheme 1) are described in the present study, differing in the inductive effect of the substituent X (X = F, Br and OCH3), in order to observe its influence, if any, on the redox potentials and biological activity of the complexes. All the synthesized ligands and the metal complexes were successfully characterized by elemental analysis, IR, UV–Vis, NMR spectroscopy and cyclic voltammetry. The molecular structures of four mononuclear (1–3 and 5) and one dinuclear (6) Ni(II) complex have been determined by X-ray crystallography. The complexes have been screened for their antibacterial activity against Escherichia coli and Bacillus. The minimum inhibitory concentrations of these complexes and their antibacterial activities indicate that compound 4 is the potential lead molecule for drug designing.

Graphical abstractSome new mixed-ligand nickel(II) complexes of three selected thiosemicarbazones {4-(p-X-phenyl)thiosemicarbazones of salicylaldehyde} (H2L1−3), where the ligands are expected to bind to nickel in a tridentate O,N,S-fashion, were prepared. To satisfy the remaining coordination sites on the metal centre, five co-ligands, viz. triphenyl phosphine, pyridine, imidazole, 4-pic (4-picoline) and 4,4′-byp (4,4′-bipyridine), were selected. The molecular structures of four mononuclear and one dinuclear Ni(II) complex have been determined by X-ray crystallography. The complexes have been screened for their antibacterial activity against Escherichia coli and Bacillus.Figure optionsDownload full-size imageDownload as PowerPoint slide