Spectral characterization and antimicrobial activity studies of 5,6-dichloro-1H-benzimidazol-2-yl-(4´/5´/6´-substituted)-phenols ($ \mathrm{HL_1}-\mathrm{HL_20} $) and Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) complexes of $ \mathrm{HL_1} $

5,6-Dichloro-1H-benzimidazol-2-yl-(4?/5?/6?-substituted)-phenols ( \mathrm{HL_1}-\mathrm{HL_20} ) and MCl2 complexes (M: Co, Ni, Cu, Zn, Pd) of \mathrm{HL_1} were synthesized and characterized by various physicochemical and spectroscopic methods such as elemental analysis, thermogravimetric analysis, FTIR, NMR and fluorescence spectroscopy. The structures of the complexes were also confirmed by performing molar conductivity and magnetic moment measurements. \mathrm{HL_1} acted as a bidentate, monobasic chelating ligand with NO donor sites in all the complexes. It was found that all complexes have non-electrolytic properties and the M:L ratios are 1:1 in the Zn(II) complex and 1:2 in the other complexes. Crystal structure of \mathrm{HL_18} was also investigated. The presence of both intra- and inter-molecular hydrogen bonding was observed in both molecules. According to the fluorescence spectral data, the substituents at the 4-position made the fluorescence emission shifted to the lower wavelengths (redshift) compared to \mathrm{HL_1} , while the substituents at the 3- and 5-positions caused a blue shift effect. The Zn(II) complex showed a greater redshift effect compared to the other complexes. In addition, antimicrobial activity of the compounds was evaluated against six bacteria and three fungi. It was observed that \mathrm{HL_1} and its mono substituted derivatives ( \mathrm{HL_1}-\mathrm{HL_11} ) show selective activity especially against Gram-positive bacteria, Staphylococcus aureus and Staphylococcus epidermidis. Zn(II) complex showed relatively higher activity against Gram-positive bacteria differently from the other complexes.