Synthesis and characterization of a novel non-symmetrical bidentate Schiff base ligand and its Ni(II) complex: electrochemical and antioxidant studies

This paper describes the synthesis and properties of a new nitro-substituted bidentate Schiff base ligand (HL) and its nickel complex (Ni(II)-2L). Its ligand was derived from the condensation of 2′-methoxyphenyl-2-ethylamine with 5-nitro-2-hydroxybenzaldehyde. This ligand and its nickel complex were characterized through elemental analysis, UV–Vis, IR, 1H NMR and 13C NMR. The molecular structure of the nickel complex was confirmed using single-crystal X-ray diffraction. This complex crystallizes in dichloromethane in triclinic system, space group of P-1 with a = 6.6803 (2), b = 9.6702 (2), c = 12.1836 (3) and 1 formula unit in the cell. The obtained data revealed that the Ni(II) center is tetra-coordinated by two oxygen and two nitrogen atoms involving two ligands. Cyclic voltammograms of the nickel complex, recorded in DMF solutions, showed one quasi-reversible redox couple related to the Ni(II)/Ni(I) couple, demonstrating its electro-activity. This indicates a slow redox transition and/or electron exchange process, which implies that this electrochemical process is mainly diffusion-controlled. The antioxidant activity of the synthesized compounds was evaluated from the reactivity with the free radical DPPH, showing IC50 values between 0.4 and 4.5 mg/mL.The authors thank the Algerian Ministry of Higher Education and Scientific Research (MESRS) and the Directorate General of Scientific Research and Technological Development (DGRSDT) for their financial support. The authors also gratefully acknowledge the financial help (MAT2016-76595-R) of the Ministerio de Economía y Competitividad and FEDER. Special thanks are owed to the Spanish Ministry of Economy and Competitiveness (MINECO) for the granting of a “Ramón y Cajal” contract (RYC-2017-23618)

Synthesis, characterization and X-ray crystal structure of novel nickel Schiff base complexes and investigation of their catalytic activity in the electrocatalytic reduction of alkyl and aryl halides

Novel potentially bidentate NO Schiff base ligands, HL1 and HL2 derived from condensation reaction of 2′-methoxyphenyl-2-ethylamine with salicylaldehyde (HL1) and with 2-hydroxy-4-methoxybenzaldehyde (HL2), and their nickel complexes were synthesized and characterized by usual spectroscopic techniques such as FT-IR, UV–Vis, 1H NMR, 13C NMR and elemental analysis. It was revealed that the bidentate Schiff base ligands coordinate with Ni(II) ions yielding mononuclear complexes with 1:2 (metal/ligand) stoichiometry. This result has been determined by using X-ray crystallographic technique of HL2 and the nickel complex derived from HL1(Ni(II)-2L1). So, the structural studies showed that the two Ni(II) complexes adopt a square-planar geometry around the central metal ion. Cyclic voltammetry studies were investigated in 0.1 M TBAP in DMF solution and indicate that the nickel complexes show one reduction wave related to Ni(II)/Ni(I) redox couple. The electrocatalytical properties of these complexes were also studied in the same electrolyte medium. Their electrocatalytic performances have been tested toward the electroreduction reaction of bromocyclopentane and iodobenzene, showing a promoted activity in the case of the Ni(II)-2L2 complex.The authors would like to thank the Algerian Ministère de l’Enseignement Supérieur et de la Recherche Scientifique et la Direction générale de la Recherche and Ministerio de Economía y Competitividad for financial support (MAT2013-42007-P). RUIZ-ROSAS Ramiro thanks Spanish Ministry of Economy and Competitiveness (MINECO) for a “Juan de la Cierva” contract (JCI-2012-12664)