A critical review of coordination chemistry of pyrimidine and pyridazine compounds: Bonding, chelation and corrosion inhibition

Metallic deterioration remains a formidable challenge in numerous industrial sectors, necessitating the continuous, intense search for effective, sustainable and non-toxic chemical inhibitors. Pyrimidines and pyridazines belong to a class of heterocycles that have garnered significant attention as potential corrosion inhibitors due to their versatile chemical configuration and promising protection performances. Notably, the nitrogen atoms in the six-membered heterocyclic ring of pyrimidine (C₄H₄N₂), pyridazine (C₄H₄N₂), and their derivatives are well known for their capacity to form coordination bonds with metal surfaces. Pyrimidine, pyridazine, and their derivatives form corrosion-inhibitive hydrophobic layers through their adsorption on the metal surfaces. The widespread conjugation of π-electrons enhances the durability and efficacy of the hydrophobic film. They demonstrate excellent inhibition efficiencies ranging from 70 to 100 % at low concentrations (<1 mM) for different metal/electrolyte systems. This review provides an overview of the properties and application of these heterocyclic compounds in chelation and coordination. Furthermore, their potential applications as aqueous phase inhibitors for different metal/electrolyte systems were comprehensively covered. Using experimental and computational tools, emphasis was placed on the coordination chemistry of pyrimidine and pyridazine, and its adsorption behaviour against metallic degradation in diverse corrosive environments was highlighted. Finally, patent literature on the effectiveness of pyrimidine and pyridazine and future perspectives were presented.