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

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 Ni-II starting materials and conditions, affording solids with divergent colors. They were characterized by elemental analysis, FTIR, UV-Vis and H-1 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 (NiN2S2)-N-II, coordinated symmetri-cally (5-5-5 membered chelate rings) when NiCl2 center dot 6H(2)O or Ni(Ac)(2)center dot 4H(2)O were used as precursors or asym-metrically (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.