Metal complexes with Schiff base and benzimidazolylphenol ligands with tert-butyl and methoxy groups: Structural characterization and biological evaluation

Two chelating ligands bearing tert-butyl and methoxy groups, an ONO type Schiff base (H2L1) and a benzimidazolylphenol derivative (HL2), NO type ligand, and their complexes with CoCl2, NiCl2, CuCl2, ZnCl2 and K2PdCl4 (1a - 1e, 2a - 2e) were synthesized and characterized. Various physicochemical and spectroscopic techniques were used to characterize the ligands. In addition, the crystal structure of H2L1 was determined by X-ray diffraction spectroscopy. Keto-enol tautomerism is observed in H2L1 according to spectral data. Elemental analysis, molar conductivity, magnetic moment, thermogravimetric analysis, FT-IR, fluorescence, UV-vis, and NMR (for diamagnetic complexes) spectroscopic techniques were utilized to characterize the complexes. Then, antibacterial, antifungal and antiviral activities of the compound were investigated. Antimicrobial activities of the compounds were tested toward six bacteria and three fungi. Some of the complexes exhibited higher activity towards some microorganisms than the ligands. HL2 and its complexes were observed to show higher activity compared to H2L1 and its complexes, especially against S. aureus, S. epidermidis, and E. coli bacteria, and the fungus C. tropicalis. It was found that 2a has a potent activity against S. aureus and E. coli, 2b against both Gram positive bacteria (S. aureus and S. epidermidis), and 2c against S. aureus, S. epidermidis and E. coli compared to other complexes. Antiviral activity of the compounds was tested against Parainfluenza Type-2 virus. In terms of antiviral effect, H2L1 showed higher activity than HL2; and the Co(II) and Cu(II) complexes of HL2 had the highest activity among the compounds, with rates of 62 % and 64 %, respectively.