Coordination of azole-type corrosion inhibitors with copper ions: A DFT study

The thermodynamics of formation of soluble coordination complexes between hydrated Cu(I)/Cu(II) ions and 19 N-heterocyclic molecules was investigated using molecular modeling based on density-functional theory and a cluster/continuum solvation model. Under the premise that adsorption of inhibitors promotes corrosion inhibition, the formation of stable soluble complexes between organic ligands and metal cations should be detrimental. The calculations revealed that the majority of the considered molecules can form stable soluble coordination complexes with copper ions, although their tendency to do so is substantially lower than that of Cl − ions. While no direct correlation was observed between the formation Gibbs energies of coordination complexes and the experimentally determined corrosion inhibition efficiencies, the results based on the Cu(II) data can nonetheless be grouped into three categories: (i) the compound is likely to act as a corrosion inhibitor if complex formation is endergonic or only weakly exergonic; (ii) for corrosion activators, complex formation is significantly exergonic; and (iii) even if complex formation is appreciably exergonic, the compound may still act as a corrosion inhibitor. • Cu coordination complexes with 19 N-heterocycles studied by DFT. • Most molecules form soluble complexes, but with substantially lower tendency than Cl − ions. • Endergonic or weakly exergonic complex formation suggests inhibitor behavior. • Corrosion activators show significantly exergonic complexation. • Corrosion inhibitors may exhibit appreciably exergonic complex formation.