Synthesis, characterization and antimicrobial activity of nickel(II) complexes of tridentate N3 ligands

The desire to develop new antimicrobial agents against the rising threat of extensive antibiotic resistance led to the exploration of many natural and synthetic compounds. Herein, we report the isolation and structural characterization of nickel(II) complexes of the type [Ni(L)2]2+ (1 and 2) of tridentate N3 ligands such as bis (pyridin-2-ylmethyl)amine (L1) and 1-(1-methyl-1H-imidazol-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L2). Both the complex cations of [Ni(L1)2]2+ (1) and [Ni(L2)2]2+ (2) possess a distorted octahedral coordination geometry in which Ni(II) is chelated to two equivalents of the tridentate L1 and L2 ligand in facial coordination, respectively. Complexes 1 and 2 exhibit the bands in the visible region in UV-Vis spectra and peaks in the downfield region in paramagnetic NMR spectra suggesting the octahedral coordination geometry of the complexes in solution as well. Further, complexes 1 and 2 were evaluated for their antimicrobial activity against various clinical pathogens. With in vitro studies, complex 1 displayed activity against Vibrio parahaemolyticus and V. alginolyticus, Staphylococcus aureus, Candida albicans, and Salmonella typhi, and complex 2 displayed activity against S. aureus, S. typhi, and C. albicans. In addition, with in vivo studies, complex 1 was effective in inhibiting Vibrio infection in brine shrimp larvae while having no toxicity on the larvae. We believe these results will encourage medicinal chemists to further the study on metal complexes against multi-resistant pathogens.