Synthesis of Nickel (II) Schiff Base Molecular Adducts: Spectroscopic Characterization & Antioxidant activity

ABSTRACT

Transition metal complexes of Ni (II) with schiff base ligand (HL) derived from condensation of 3-Bromo benzaldehyde and hydrazine monohydrate were successfully synthesized , characterized and isolated .The schiff base ligand and its Ni(II) complexes prepared were characterized by melting  point /decomposition temperature, solubility, conductivity/ Molar conductance, UV- visible, FT-IR, XRD, TGA and elemental analysis results. In the UV-Vis study, a bathochromic shift of approximately 60 nm indicating the formation of coordinated Ni(II) complexes by more than one coordinating sites . IR spectra of the free ligand  showed a band at 1660cm^-1 which is assigned to the (-C=N-) stretching vibration of the azomethine functional group. These bands were observed at lower frequencies in the spectra of Ni(II) complexes which indicates complexation process between schiff base ligand  and Ni²⁺ ion . Low conductance (7-9 ohm^-1 cm² Mol^-1) measurement indicated that the Ni (II) complexes are non electrolytic in nature whereas elemental analysis result revealed 1:1 Nickel-schiff base ratio. TGA analysis showed the presence of two coordinated water molecules on the basis of physico chemical measurements the following empirical formulas have been assigned to coordinated Ni(II) complex : [ Ni(HL)₂ ] 2Cl. 2H₂O, [ Ni(HL)₂ ] SO₄ .2H₂O. The antioxidant activities of schiff base ligand and Ni(II) complexes were evaluated by using DPPH reagent ie, 2_, 2^’- diphenyl -1-picrylhydrazyl free radical assay which showed that coordinated Ni(II) complexes have a higher antioxidant activities than that of Schiff base ligand. All compounds have been evaluated for invitro anti microbial activities against isolated bacterial strains of  E. coli (MTCC-1687), E. faecalis (MTCC-439), S. aureus (MTCC-737) and MR S. aureus (Indigenous) .All compounds showed mild to moderate antibacterial activities. The minimum inhibitory concentration values ranged from 50 g/ml to 3.125 g/ml. All compounds displayed invitro anti bacterial activity against both gram positive and gram negative bacterial strains. It may be proved that the antibacterial activity of compounds is related to the cell wall structure of the tested bacterial stain. The synthesis of Ni(II) complexes via template method is a good method for obtaining very efficient bioactive agents as a good drug candidates for various biological applications in future for humans. As well as schiff base molecular adducts of Ni(II) complexes are also promising material in different cutting edge research areas like applications in preparation of solar cells, super capacitors, catalysts and electrode materials.

Keywords: Schiff base ligands, Ni(II) complexes, Spectroscopic analysis, antioxidant activities, Antimicrobial activities, DPPH, 3-Bromobenzaldelyde