Synthesis, structural and corrosion inhibition properties of some transition metal(II) complexes with o-hydroxyacetophenone-2-thiophenoyl hydrazone

Abstract

A series of metal complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with o-hydroxyacetophenone-2-thiophenoyl hydrazone (Hhath) have been synthesized. The metal complexes were characterized with the help of elemental analyses, magnetic susceptibility measurements, electronic, IR, NMR and ESR spectral techniques. The structures of Hhath ligand and its Mn(II) complex were determined by single crystal X-ray diffraction studies. Hhath displays E configuration about the >CN– bond. The molecular structure of ligand is stabilized by inter- and intra-molecular H-bonding whereas, [Mn(hath)2] complex is stabilized by π–π and C–H⋯π interactions. In all the complexes, ligand behaves as mono-anionic tridentate and binds to the metal ions via deprotonated phenolate-oxygen, carbonyl-oxygen and azomethine-nitrogen. Magnetic moments and electronic spectral studies suggest an octahedral geometry around metal ion in all the complexes. Frozen solution ESR spectra of Cu(II) complex in DMSO gives axial signal and suggests 2B1g as the ground state. The ligand and its metal complexes showed appreciable corrosion inhibition activity against corrosion of mild steel in 1M HCl solution. The inhibition efficiency of the inhibitors was found to increase with time up to 12h and thereafter almost constant. The metal complexes showed greater inhibition efficiency than the free ligand.