Structural characterization and antimicrobial activity of 2-[4,6-(Cl/CH3/CF3)-benzimidazol-2-yl]-4-(OCH3/Br)-phenols and their Zn(II), Pd(II) and Au(III) complexes

2-[4,6-{Dichloro/dimethyl/bis-(trifluoromethyl)}-benzimidazol-2-yl]-(5-bromo/methoxy)-phenols (HL1 – HL6) and their complexes with ZnCl2, PdCl2 and AuCl3 were synthesized and characterized. The structures of the complexes were confirmed on the basis of elemental analysis, molar conductivity, FT-IR, NMR and fluorescence spectroscopy. Most of the complexes are four-coordinated with a 1:2 M:L ratio and the Au(III) complexes are 1:1 electrolyte whereas the others are non-electrolyte. According to the fluorescence spectra, electronegative substituents such as bromo, chloro, trifluoromethyl and methoxy were found to increase red shift (shifting to higher wavelength). The highest wavelength was observed to belong to HL6 (trifluoromethyl-methoxy derivative) with 531 nm. When compared to the ligands, there is decreasing in the red shift and fluorescence intensity in the spectra of the complexes. In addition, antimicrobial activity of the compounds was evaluated against six bacteria and three fungi. The Au(III) complexes have superior activity against all the bacteria, while the Pd(II) complexes showed higher antifungal activity than the ligands and metal salt.