Three routes to nickel(ii) salicylaldehyde 4-phenyl and 4-methylthiosemicarbazonato complexes: Mechanochemical, electrochemical and conventional approach

In the synthesis of Ni(ii) salicylaldehyde 4-phenyl and 4-methyl-thiosemicarbazonato complexes conventional, electrochemical and mechanochemical routes were applied and compared. Polynuclear tetrahedral [Ni(sal 4-Metsc)]_n (1) and mononuclear square planar [Ni(sal 4-Phtsc)(H₂sal 4-Phtsc)]·CH₃OH (2) were obtained by the conventional method. The electrochemical synthesis proved to be a simple and efficient route for the synthesis of brownish-red single crystals of square planar (2) and polycrystalline green octahedral [Ni(Hsal 4-Metsc) ₂]·(3) complexes, while the liquid-assisted mechanochemical synthesis was a fast route for the synthesis of green octahedral [Ni(Hsal 4-Metsc)₂]·(3) and [Ni(Hsal 4-Phtsc)₂]·(4). The advantages and disadvantages of all used synthetic methods were discussed. The characterization of square planar (2) and two octahedral complexes (3) and (4) was performed by X-ray diffraction methods, infrared and NMR spectroscopy. In addition quantum chemical calculations were performed for CS (conformer which enables O-H⋯S intramolecular hydrogen bond formation in 2-hydroxyaryl Schiff base thiosemicarbazones) and SC (conformer with the thiocarbonyl group turned away from O-H⋯N intramolecular hydrogen bond) forms of both ligands and in each case the CS conformer was lower in energy.