Iron(III) and nickel(II) complexes of O,N,N,O-chelating benzophenone thiosemicarbazone: Electrochemistry and in situ spectroelectrochemistry

New complexes, [Fe(L)Cl] (1 and 2) and [Ni(L)]·C2H5OH (3 and 4), were synthesized by template condensation of 2,4-dihydroxy-benzophenone-S-methyl-thiosemicarbazone with 5-bromo- and 5-chloro-2-hydroxy-benzaldehyde and characterized by elemental analysis, conductivity measurements, IR, NMR and mass spectra. Complex 4 crystallizes in monoclinic space group P21/c with unit cell dimensions, a = 13.1091 (3) Å, b = 24.2308 (3) Å, c = 15.5808 (4) Å, β = 102.2632 (11)°, V = 4836.22 (18) Å3, Z = 8. The asymmetric unit of 4 contains two main molecules and two ethanol molecules. Electrochemical behaviors of 1–4 were studied using cyclic voltammetry and square wave voltammetry. Voltammetric analysis of the complexes shows a quasi-reversible metal-based reduction processes between −0.55 and −0.78 V followed by an irreversible reduction process within −0.91 and −1.27 V versus SCE. An irreversible oxidation is also observed within −1.10 to −1.23 V versus SCE during anodic potential scans. While the thiosemicarbazone moiety stabilizes +3 and +2 oxidation states for the iron complexes, only NiII is stable in solution with the same ligand in dichloromethane and dimethylsulfoxide. In-situ spectroelectrochemical studies were employed to determine the colors and spectra of electrogenerated species of the complexes.