Synthesis, characterization, and X-ray crystal structures of copper(II) and nickel(II) complexes with two bis(thiosemicarbazone) ligands and investigation of their electrochemical behavior

Two new bis(thiosemicarbazone) ligands having a halogen substituent on the non-coordinating phenyl rings, namely 2-[1-(2-{3-[2-({2-[(4-bromoanilino)carbothioyl]hydrazono} methyl)phenoxy]propoxy}phenyl)methylidene]-N1-(4-bromophenyl)-1-hydrazinecarbothiamide (H2L3) and 2-[1-(2-{3-[2-({2-[(4-bromoanilino)carbothioyl]hydrazono}methyl)phenoxy]-2-hydroxypropoxy}phenyl) methylidene]-N1-(4-bromophenyl)-1-hydrazinecarbothiamide (H3L4), were used in the synthesis of a series of CuII and NiII complexes [Cu(L3)]·MeOH, [Cu(HL4)], [Ni(L3)], and [Ni(HL4)]·MeOH. The complexes were characterized by physicochemical and spectroscopic methods. Single-crystal X-ray structures of [Cu(L3)]·MeOH, [Cu(HL4)], and [Ni(L3)] showed that the metal centers are coordinated by two imine nitrogen atoms and two sulfur atoms in a distorted square-planar coordination geometry. Electrochemical investigations showed that all of these CuII and NiII complexes were reversibly reducible. Although the bromine substituent on the phenyl ring and the hydroxyl group are far from the metal centers, they have an effect on the redox potentials of the NiII/I and CuII/I couples.