X-ray crystal structural and spectral studies of copper(II) and nickel(II) complexes of functionalized bis(thiosemicarbazone) ligands and investigation of their electrochemical behavior

Abstract

Neutral bivalent copper and nickel bis(thiosemicarbazone) complexes bearing the methoxy and bromine substituents on the dialdehyde-backbone of the ligand have been synthesized. All of them have been characterized by spectroscopic methods and in two cases by X-ray crystallography. Upon formation of these complexes, the each two bis(thiosemicarbazone) arms is deprotonated, acting as dianionic, tetradentate N2S2 ligands. The geometrical distortion from square planar in the copper complex is very greater than the nickel complex. Cyclic voltammetry studies of Cu(II) and Ni(II) complexes in DMF show that all complexes are able to stabilize low oxidation states of Cu(I) and Ni(I). The introduction of different substitutions on the aromatic ring attached to the imine carbon led to two consequences. First, The E1/2 values for the CuI/CuII and NiI/NiII redox couples were cathodically shifted in comparison with the unsubstituted analog. Second, the copper complexes underwent a quasi-reversible one-electron oxidation (CuII/CuIII).