Synthesis, structural and corrosion inhibition studies on cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone

Cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, electronic, IR, NMR and ESR spectral techniques. The molecular structures of ligand and its copper(II) complex have been determined by single crystal X-ray diffraction technique. The Cu(II) complex possesses a CuN2O2 chromophore with a considerable delocalization of charge. The structure of the complex is stabilized by intermolecular π–π stacking and C–H⋯π interactions. Hatbh acts as a monobasic bidentate ligand in all the complexes bonding through a deprotonated C–O− and >CN groups. Electronic spectral studies indicate an octahedral geometry for the Ni(II) complex while square planar geometry for the Co(II) and Cu(II) complexes. ESR spectrum of the Cu(II) complex exhibits a square planar geometry in solid and in DMSO solution. The trend g|| > g⊥ > 2.0023 indicates the presence of an unpaired electron in the dx2-y2dx2-y2 orbital of Cu(II). The electro-chemical study of Cu(II) complex reveals a metal based reversible redox behavior. The Ni(II) complex shows exothermic multi-step decomposition pattern of the bonded ligand. The ligand and its most of the metal complexes show appreciable corrosion inhibition properties for mild steel in 1 M HCl medium. [Co(atbh)2] complex exhibited the greatest impact on corrosion inhibition among the other compounds.

Graphical abstractThe complexes of Co(II), Ni(II), Cu(II), and Zn(II) with 2-acetylthiophene benzoylhydrazone have been synthesized and characterized by magnetic moments, electronic, IR, NMR and ESR spectra. Molecular structure of ligand and its Cu(II) complex were determined by single crystal X-ray diffraction. Corrosion inhibition by ligand and its metal complexes was also evaluated.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The copper(II) complex exhibits π–π and C–H⋯π interactions. ► Spectral studies of complexes show variations in bonding mode and stereochemistry. ► ESR spectrum of Cu(II) complex indicates square planar geometry around metal ion. ► Electrochemical study of [Cu(atbh)2] shows reversible redox behavior. ► Most of the complexes show an appreciable anti-corrosion behavior.