Molecular structure determination of Nickel(II) isomers bearing bis(thiosemicarbazone) ligands: X-ray, DFT calculations and kinetic groundwork

Abstract

The formation of isomers can be stimulated by many factors and their properties are often used in the development of new catalysts, optical devices and drugs. Herein, reactions between benzyl-bis(thiosemicarbazones) ligands, so called H2LR (R = Me or Et), were investigated with different NiII starting materials and conditions, affording solids with divergent colors. They were characterized by elemental analysis, FTIR, UV–Vis and 1H NMR spectroscopies, as well as cyclic voltammetry, which revealed distinct products from the respective NiII starting precursors. However, the ESI(+)-MS the products of each ligand presented almost identical m/z patterns, independently from their precursors. Remarkably, the structures of both products were determined by single-crystal X-ray diffraction, showing the formation of two isomers of the type NiIIN2S2, coordinated symmetrically (5–5–5 membered chelate rings) when NiCl2·6H2O or Ni(Ac)2·4H2O were used as precursors or asymmetrically (4–6–5 membered chelate rings) upon reaction with [Ni(acac)2]. Theoretical calculations by DFT were also accomplished to explain the electronic spectra of the two products and to calculate the thermodynamic parameters related to the stability of the two isomers. Finally, a kinetic study was performed to investigate the formation of the asymmetrical and the symmetrical complexes.