Spectral characterization and antimicrobial activity of 2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols and their zinc(II) complexes

2-(5-Chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols (HLx; x = 1–4) and their complexes with zinc(II)nitrate have been synthesized and characterized. In the tetrahedral mononuclear complexes, the ligands are bidentate, via the imine nitrogen and the phenolate oxygen atoms. The structures of the complexes were confirmed on the basis of elemental analysis, molar conductivity, TGA, FT-IR, NMR, mass and UV–vis spectroscopy. The optimized geometry of the complexes was derived from theoretical calculation in DGauss/DFT level on CACHE program. From theoretical calculations it was found that bromo derivatives of the ligands (HL1 and HL3) have higher stability than the other ligands and similarly, their Zn(II) complexes have higher stability than the other complexes. The antimicrobial activities of the compounds were evaluated using the disk diffusion method against six bacteria and Candida albicans. All of the complexes exhibited selective antibacterial activity on Staphylococcus epidermidis. HL3 and [Zn(L1)2]·H2O are more active than Ciprofloxazin and, [Zn(L2)2] has antibacterial activity as potent as Ciprofloxazin against S. epidermidis.