A dithiocarbazate N,S Schiff base ligand with a long alkyl chain: Synthesis, characterization, DFT study and antimicrobial activity of its Ni(II) complex

The N,S bidentate ligand S-hexyl-β-N-(4-nitrobenzylidene)dithiocarbazate (HL), obtained by condensation of S-hexyldithiocarbazate with 4-nitrobenzaldehyde, has been used to synthesize the nickel(II) complex, NiL₂. The ligand and complex were characterized by physicochemical techniques and the nickel species also by single crystal X-ray diffraction. The metal is four-coordinated with trans configuration of the Schiff bases that chelate the metal in the deprotonated monoanionic form. When compared to the free ligand, the metal complex exhibits a considerable increase in fluorescence intensity. Hirshfeld surface analysis and quantum chemical density functional theory (DFT) calculations were conducted to evaluate the non-covalent interactions of the complex NiL₂. The antibacterial activity of free ligand HL and the complex was evaluated in vitro against pathogenic gram-negative bacteria, Escherichia coli and Klebsiella pneumonia. The test showed that neither the HL alone nor the complex were found to exhibit any activity against the tested organisms.