A comprehensive review on pyrazole derivatives as corrosion inhibitors: Ligand properties, coordination bonding, and interfacial adsorption

Metal corrosion poses a critical challenge across industrial sectors, driving the persistent search for efficient, environmentally friendly, and non-toxic inhibitors. Pyrazole and its derivatives, as five-membered nitrogen-containing heterocyclic compounds, have garnered significant interest due to their robust coordination capabilities and superior corrosion inhibition performance. Nitrogen atoms and delocalized π-electrons in the pyrazole (C₃H₄N₂) ring facilitate strong adsorption onto metal surfaces, forming protective hydrophobic layers that mitigate corrosion. This adsorption primarily involves a combination of physisorption and chemisorption, with the dominant mechanism depending on the metal-electrolyte system and functional groups present in the pyrazole derivatives. The presence of two vicinal (1,2-) nitrogen atoms makes the pyrazole ring an electron-rich species, offering strong coordination bonding and excellent ligand and coordinating properties through π-electron interaction. Their non-innocent ligand property, which allows them to donate and accept electrons, makes them capable of robust binding and adsorption on metallic substrates. The presence of additional functional moieties and their tautomeric flexibility enhance their capacity to provide adequate surface adsorption and coverage. These inhibitors exhibit remarkable inhibition efficiencies, manifesting as much as 98 % efficiency. This article examines pyrazole derivatives' capacity to suppress corrosion, particularly their electrical effects, ligand characteristics, coordination bonding, and interfacial characteristics. On metallic substrates such as Fe, Al, Zn, Cu, and galvanized-Fe, it talks about how stable and effective these derivatives are. With an emphasis on pyranopyrazoles, the study also discusses the sustainability and green features of pyrazole-based corrosion inhibitors. To enhance adsorption and inhibitory potential, it also covers chemical functionalisation and synergism techniques.