Synthesis, spectroscopic characterization, DFT, oxygen binding, antioxidant activity on Fe(III), Co(II) and Ni(II) complexes with a tetradentate ONNO donor Schiff base ligand

Abstract

The Schiff base ligand, namely (7E)-N-benzylidene-2-styrylbenzenamine- 1,2-diamine-2,4-dihydroxy-phenol (L), was synthesized by condensation of 2,4-dihydroxybenzaldehyde with o-phenylenediamine. The reaction of the ligand with Fe(III), Co(II) and Ni(II) salts in an 1:1 ratio yielded three complexes (1?3). Different analytical tools, like elemental analysis, ESI-MS, UV?Vis, FT-IR, NMR and EPR spectroscopy, then molar conductivity and magnetic susceptibility spectra, were used to elucidate the structure of the ligand and complexes. Density functional theory calculation at the B3LYP/3- -211G++/LANL2DZ level of the theory has been carried out to optimize the geometry of the ligand and complexes. The tetradentate ligand has coordinated to metals through ONNO donors affording octahedral geometry. Complexes were studied for their oxygen-binding activity and free radical scavenging activities. Complexes 1 and 2, which contain Fe(IIl) and Co(II), displayed reversible oxygen binding activity. On the other hand, complex 3 fails to show oxygen binding. The order of antioxidant activity is: 3 > 1 > 2 > L.