Ultrasonic assisted synthesis, crystallographic, spectroscopic studies and biological activity of three new Zn(II), Co(II) and Ni(II) thiosemicarbazone complexes as precursors for nano-metal oxides

[Display omitted] •New Zn(II), Co(II) and Ni(II) thiosemicarbazone complexes have been synthesized.•The direct thermolysis of thiosemicarbazone complexes led to nano-sized metal oxides.•The in vitro antibacterial activities were studied. Using ultrasonic irradiations, three new complexes of type [ZnL2].CH3CN, [NiLCl] and [CoL2] (where L is 2-acetylpyridine-4N-p-chlorophenylthiosemicarbazone ligand) have been prepared and investigated using various spectroscopic methods. Crystal structures of ZnL2 and NiLCl complexes displayed distorted octahedral and square-planar coordination geometry around the central metal, respectively. The UV-visible and mass spectroscopic analysis revealed 1:2 (metal:ligand) stoichiometry for Co(II) complex. The synthesized complexes have been used as precursors for preparing their corresponding nano-sized metal oxides via thermal decomposition. The nanostructures of metal oxides were characterized by scanning electron microscope (SEM), energy dispersive X-ray (EDX), X–ray diffraction (XRD) and Fourier transform infrared (FT–IR). The in vitro antibacterial activity of thiosemicarbazone complexes and their corresponding nano-sized metal oxides were studied against a series of gram positive and gram negative bacteria, using the zone inhibition methods. While NiLCl complex was shown to possess more antimicrobial activity than its nano-sized metal oxide, the prepared nano-sized zinc and cobalt oxides have shown the highest activity.