Synthesis, crystallography, and conducting properties of a new nickel(II) complex containing 4-(diphenylamino)benzaldehyde-4-(ethyl)thiosemicarbazone

A new Nickel(II) complex, NiL2, was prepared in this study by reacting 4-(diphenylamino)benzaldehyde-4-(ethyl)thiosemicarbazone and nickel(II) acetate. The resulting NiL2 complex was thoroughly characterized by a variety of methods, such as elemental analysis, fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, magnetic susceptibility, and molar conductivity measurements. The material was also analyzed using a single-crystal X-ray diffraction (SCXRD) to identify its structural characteristics. FTIR confirmed that the ligand was bound to Ni(II) in a mononegative bidentate fashion through the azomethine (N=C) and thione sulfur (C=S) donor atoms. The UV-Vis spectrum and the measured magnetic moment are consistent with a diamagnetic species (μeff ≈ 0 BM), indicating a square planar geometry, which was confirmed by X-ray crystallographic data. The structural analysis showed a distorted square planar geometry with bond angle deviations up to 6°. The complex crystallized in the triclinic P-1 space group and adopted the thione tautomeric form. Moreover, NiL2 was used as a dopant in solid biopolymer electrolyte (SBE) films prepared by the solution-casting technique using carboxymethyl cellulose (CMC) as the polymer host, polyethylene glycol (PEG) as a plasticizing agent, and isophthalic acid (IA) as the protonator. The highest ionic conductivity of 4.60 × 10-7 S cm-1 at 353 K was achieved with CMC (1 g) + PEG (0.1 mL) + NiL2 (15 wt%) + IA (20 wt%) of the SBE composition. In addition, the conductivity follows the Arrhenius behavior with an activation energy (Ea) of 0.144 eV, indicating that it requires low thermal energy to activate the charge carrier.