Nickel(II) and Palladium(II) complexes with imine-based tridentate ligand: Synthesis, spectral characterization, Antimicrobial, cytotoxicity and DFT studies

The organic compound (Z)-2-bromo-2-(5-bromo-2-hydroxy-3-methoxybenzylidene)-N-metylhydrazine-1-carbothioamide (L1H2) and its nickel(II) complex [Ni(L1)(PPh3)](1) and palladium(II) complex [Pd(L1)(PPh3)](2) were synthesized and characterized using various spectroscopic methods, including NMR,FT-IR, HRMS, and UV–Vis spectroscopy. Single-crystal X-ray diffraction analysis was used to determine the crystal structures of [Ni(L1)(PPh3)](1) and [Pd(L1) (PPh3)](2). The Hirshfeld surface analysis was used to study various interactions in the crystal structure of complexes. In addition, an energy framework computational analysis was also done to gain a further understanding of the structural details of the complexes. DFT-based calculations were done for the ligand and its associated metal complexes to establish the correlations between their structural characteristics and integral properties. Ligand and its complexes were evaluated for their antimicrobial effects. The antimicrobial effects of ligands and their complexes were assessed. It was found that both Ni(II) and Pd(II) complexes showed better antimicrobial activity.The minimum inhibitory concentration for the [Ni(L1)(PPh3)] complex ranges from 1.95–250 µM; for the [Pd(L1)(PPh3)] complex, it ranges from 3.5–250 µM; and for the ligand, it ranges from 62.5–250 µM against both bacterial and fungal strains. The synthesized compounds were tested for anti-proliferative assays against the HELA carcinoma cell line. The IC50 values obtained were 98.83 µM for the ligand, 83.09 µM for the Ni(II) complex, and 86.74 µM for the Pd(II) complex, suggesting Ni(II) complex a stronger anti-cancerous agent compared to the Pd(II) complex.Noteworthy, both complexes and standard drugs (ciprofloxacin and nystatin) showed non-cytotoxic behavior towards the normal HEK-293 cell line. The increased efficacy and selective cytotoxicity of the complexes highlight their potential as a candidate for further investigation and development into a potent therapeutic agent as an antimicrobial and anticancer agent.