Abstract
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.
Highlights
Schiff bases are compounds that are comparable to ketone or aldehyde, they have azomethine (HC=N) group instead of the carbonyl (C=O) group in the carbonyl compounds
The mixed-ligand complexes have higher melting points than the parent Schiff base ligands, this showed that they have better stability than the Schiff bases
Elemental analyses data indicated the formation of 1:1:1 [nickel:Schiff base:ammonia] molar ratio for the mixed-ligand complexes
Summary
Schiff bases are compounds that are comparable to ketone or aldehyde, they have azomethine (HC=N) group instead of the carbonyl (C=O) group in the carbonyl compounds. R2 can either be an alkyl or aryl group[4,5,6] They are significant chelating ligands in coordination chemistry. Studies showed that Schiff bases derived from salicylaldehyde, 2-hydroxyl-1-naphthaldehyde including the derivatives and complexes with some transition metals displayed significant biological properties which make them gain attention. This study, which synthesized, characterized, and carried out the biological and theoretical studies of nickel(II) mixed-ligand complexes of tridentate Schiff bases and ammonia. The molecular structures of the Schiff base ligands and complexes were modelled, and the theoretical calculations were carried out on their optimized structures. These were utilized for their IR, UV-Vis and NMR spectra. A consideration of the similarities between the calculated and experimental spectra, mostly the electronic spectra could further be used for identification of the molecular geometry
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