Pyrazole ligands and their monometallic and bimetallic complexes: synthesis, characterization, and application as novel corrosion inhibitors

A series of pyrazole ligands named as 1,4-bis(3,5-dimethylpyrazol-1-yl)butane (bbd), 1,3-bis(3,5-dimethylpyrazol-1-yl)propane (bdpp), and 1,3-bis(3,5-dimethylpyrazol-1-yl)propane-2-ol (bdpo) along with their transition metal complexes including [Cu2(µ3-SCN)2(µ-bbd)]n, [Cu2(µ3-SCN)2(µ-bdpp)]n, and [Cu2Hg(µ2-SCN)2(bdpo)2(CH3COO)2]n were synthesized and characterized using FT-IR and Uv-vis spectroscopies, as well as thermal gravimetric analysis. The prepared compounds were investigated as corrosion inhibitors to protect mild steel in 0.5 M H2SO4 solution. Corrosion tests were performed by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The pyrazole ligands exhibited inhibition efficiencies in a range of 38–78%, which introduced them as moderate inhibitors. On the other hand, the pyrazole complexes showed inhibition efficiencies higher than 85%, demonstrating their high potentials to mitigate the steel corrosion. In addition, the bimetallic complex resulted in higher corrosion resistance than the two monometallic complexes. This was evidence of a critical role of the coordinated metal of the complex in forming an adhesive protection film on the steel surface.