New nickel (II) and copper (II) bidentate Schiff base complexes, derived from dihalogenated salicylaldehyde and alkylamine: Synthesis, spectroscopic, thermogravimetry, crystallographic determination and electrochemical studies

Nickel and copper metal complexes of bidentate Schiff base ligand (HL) were synthesized in methanolic solution from a condensation reaction of alkylamine (4-methoxyethylphenylamine) and dihalogenated salicylaldehyde (3,5-dichlorosalicylaldehyde). Their structures have been elucidated using various conventional spectroscopic techniques such as elemental analyses, nucleic magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, electronic spectroscopy and thermogravimetry analysis. The Schiff base nickel complex was characterized by X-ray structural analysis at 170 (2) K. This compound crystallizes in the triclinic space group P-1, with unit cell parameters: a = 6.233 (5)angstrom, b = 8.586 (5) angstrom, c = 15.247 (5)angstrom, beta = 98.324 (5)degrees. Structural analysis of the ligand showed two coordinated centers through iminic nitrogen atom and phenoxy oxygen atom leading to a distorted square-planar geometry. The molar conductance values effectively confirmed the non-electrolytic nature of the both complexes. Ultraviolet visible (UV-Vis.) spectra were performed in order to resolve the expected pi-pi * and n-pi* azomethine electronic transitions of the ligand and the both complexes. The thermal decomposition of the synthesized complexes was studied by thermogravimetry and differential thermogravimetry (TG/DTG) between 25 and 800 degrees C using four different heating rates 5, 10, 15 and 20 degrees C/min. Four methods from the literature have been chosen to estimate the values of the activation energies and the pre-exponential factors of the thermal decomposition; those of Kissinger, Ozawa, Friedman and Coats-Redfern. Thermodynamic parameters such as Delta S, Delta H and Delta G were determined by using the Coats-Redfern's method. The electrochemical process was carried out by cyclic voltammetry (CV) in a tetrabutylammonium perchlorate (TBAP)/dimethylformamide (DMF) 10(-1) M as an electrolyte support. The prepared Schiff-base metal complexes displayed similar cyclic voltammetric behavior, exhibiting a quasi-reversible cathodic redox couple M(II)/M(I). (C) 2020 Elsevier Ltd. All rights reserved.