Tailored synthesis of unsymmetrical tetradentate ONNO schiff base complexes of Fe(III), Co(II) and Ni(II): Spectroscopic characterization, DFT optimization, oxygen-binding study, antibacterial and anticorrosion activity

Two Schiff base ligands namely bis-2-((1E)-((Z)-2-(1,2-diphenylethylideneamino) phenylimino)methyl) phenol (L-1) and bis-2-((1E)-((E)-2-(1-phenylethylideneamino)phenylimino) methyl)phenol (L-2) were synthesized by tailored reaction of o-phenylenediamine with o-hydroxybenzaldehyde and 2-hydroxy-1,2-diphenylethanone/o-hydroxyacetophenone. The reaction of these ligands with Fe(III), Co(II), and Ni(II) salts yielded six complexes. Ligands and their metal derivatives have been characterized by elemental analysis, molar conductance, magnetic susceptibility, FT-IR, UV-Vis, ESI-mass, H-1 NMR, C-13 NMR and EPR analysis. Using Gaussian 09 molecular modelling, bond lengths, bond angles and Mulliken charge were also evaluated. In addition to this study of HOMO and LUMO molecular orbital have been performed. The FT-IR spectra have suggested that ligand is coordinated with metal through azomethine-N and phenolic-O. Experimental and theoretical IR and NMR spectrum of ligand L1 and complex 2 exhibits quite good correlation. ESR spectrum of complex 2 at LNT suggests octahedral geometry around Co(II). Complexes were studied for their oxygen-binding activity and displayed significant oxygenation reaction. The thermodynamic parameters such were also calculated. The compounds were screened for antibacterial activity against gram-negative bacteria Escherichia coli and compared with Amoxicillin. Complexes have exhibited significant antibacterial activity. The corrosion inhibition effect of ligands and complexes on mild steel in acidic medium was studied for 24, 48 and 72 h using weight loss measurement. (C) 2019 Elsevier B.V. All rights reserved.