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Ni(II) mixed-ligand complexes of [NiLNH3] (where L= N-salicylidene-o-aminophenol (L1), N-(5-methoxysalicylidene-o-aminophenol) (L2) and N-(2-hydroxy-1-naphthalidene)-o-aminophenol) (L3) containing ONO tridentate Schiff bases and ammonia were synthesized and characterized by elemental analysis, infrared, ultraviolet-visible, proton and carbon-13 spectroscopies. Theoretical calculations were also performed on the optimized structures of the Ni(II) mixed-ligand complexes. The Infrared and ultraviolet-visible spectra of the complexes were calculated, and the results compared with the corresponding experimental spectra to augment the experimental structural identification. The elemental analysis data confirmed the formation of 1:1:1 [metal: Schiff base: ammonia] molar ratio. The NMR spectra showed that the Schiff bases coordinated to the Ni(II) ion via the two deprotonated phenolic oxygen and azomethine nitrogen atoms. The biological studies showed that the complexes exhibited higher antibacterial and antioxidant activities than the free Schiff base ligands.

The computational modelling and total antioxidants activities of three N-(methoxysalicylidene) anilines namely N- (methoxysalicylidene)aniline [I], N-(methoxysalicylidene)-4-chloroaniline [II] and N-(methoxysalicylidene)-5-chloro-2-methylaniline [III] were reported. The compounds were synthesized and characterized by elemental analysis, infrared, ultraviolet, proton and carbon-13 nuclear magnetic resonance. Quantum chemical computations were also performed on the optimized structures of the compounds using Density Functional Theory. The infrared, nuclear magnetic resonance and ultraviolet spectra of the compounds were calculated and the results likened to the equivalent experimental spectra to enhance the structural identification. The calculated infrared, nuclear magnetic resonance and ultraviolet spectra were comparable to the experimental spectra. The total antioxidant capacities of the Schiff bases were evaluated by phosphomolybdenum assay and the results indicated that all the synthesized compounds displayed antioxidant activities.

Three substituted monodentate salicylaldimines namely 5-chloro-N-[(2- methoxy) phenyl] salicylaldimine [I],  5-chloro-N-[(4-chloro)phenyl]salicylaldimine [II] and 5-chloro-N-[(2-methyl-5-chloro)phenyl] salicylaldimine [III] were synthesized and characterized by elemental analysis, IR, UV, 1H and 13C NMR. Theoretical calculations were also performed on the optimized structures of the compounds. The IR, NMR and UV spectra of the compounds were calculated and the results compared with the corresponding experimental spectra to augment the structural elucidation. The calculated IR, NMR and UV values were in agreement with the experimental results. The total antioxidant capacities of the compounds were determined by phosphomolybdenum assay.