A square-pyramidal iron(III) complex obtained from 2-hydroxy-benzophenone-S-allyl-thiosemicarbazone: synthesis, characterization, electrochemistry, quantum chemical studies and antioxidant capability

Abstract

2-Hydroxybenzophenone-S-allyl-thiosemicarbazone and 3-allyl-salicylaldehyde were condensed by template effect of iron(III) ion to yield the N2O2 type-chelate complex. The S-allyl-thiosemicarbazone (1) and the iron(III) complex (2) were characterized by elemental analysis, magnetic measurements, electronic, infrared, Raman and H-1-NMR spectra, and also single-crystal X-ray diffraction technique. Electrochemical characterization of the iron(III) complex was carried out by using cyclic voltammetry. The complex gives a metal based one electron reversible Fe-III/Fe-II reduction and, S-allyl-thiosemicarbazone-based oxidation and reduction reactions. The reduction potentials of the S-allyl-thiosemicarbazone and the complex are calculated in terms of Gibbs free energy change of the redox reaction at the theory level of UwB97XD/LANL2DZ/PCM. The optimized geometries and vibrational frequencies of the compounds were calculated using the DFT/UwB97XD method with the 6-31 G(d,p) basis set and compared to experimental data. TD-DFT was employed to examine the electronic transitions of the complex and to conduct the NBO charges at the same level. For the compounds, in vitro total antioxidant capacity (as TEAC coefficient) and scavenging activity of reactive oxygen species (ROS) which are hydroxyl radical (center dot OH), superoxide anion radical (center dot O-2-), and hydrogen peroxide (H2O2) have been determined by using spectroscopic methods.