Four new stable nickel(II) complexes (1e4) with isothiosemicarbazone- and thiosemicarbazone-based ligands, namely, salicylidine S-propyl-isothiosemicarbazone hydroiodide (H2L1.HI), 5-bromo-2- hydroxybenzaldehyde S-propyl-isothiosemicarbazone hydroiodide (H2L2.HI), salicylidinethiosemicarbazone (H2L3), and 5-bromo-2-hydroxybenzaldehyde thiosemicarbazone (H2L4) accompanied with triphenylphosphine and 2-methylimidazole as ancillary ligands were prepared in good yields. The complexes were characterized using analytical and spectroscopic techniques. Single-crystal X-ray crystallography revealed that the nickel complexes had distorted square planar geometries. H2L1.HI and H2L2.HI acted as NNO, while H2L3 and H2L4 acted as SNO tridentate donor ligands. In vitro antifungal and antibacterial activities of the Ni(II) complexes revealed that 3 exhibited the highest antifungal property especially against Candida albicans with an inhibition zone of 40mm and a minimum inhibitory concentration, MIC ¼ 1.56 mg/ml). Complex 2 showed the highest antibacterial property especially against Staphylococcus aureus with an inhibition zone of 30mm and MIC of 1.56 mg/ml. Results indicate that these complexes are potential antimicrobial drugs for the treatment of infectious diseases for further research.

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