A theoretical study on the corrosion inhibition of Cu surfaces using 4-amino-3-thioxo-6-methyl-1,2,4-triazine-5-one and its derivatives.

The current study focused on evaluating the behavior of 4-amino-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2 H)-one (1a) along with its tautomers, as well as 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2 H)-one (2a) and its tautomers as potential corrosion inhibitors for copper surfaces with two different miller indices namely Cu (1 1 1) and Cu (1 1 0) by employment of a DFT approach. Among different tautomers, the most negative adsorption energies were observed for the following compounds: 4-amino-3-thioxo-3,4-dihydro-1,2,4-triazin-5(6 H)-one (1c), 4-amino-5-hydroxy-1,2,4-triazine-3(4 H)-thione (1d), 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(6 H)-one (2c), and 4-amino-5-hydroxy-6-methyl-1,2,4-triazine-3(4 H)-thione (2d). Critical parameters associated with the molecular performance of triazine derivatives as corrosion inhibitors include the EHOMO, ELUMO, ΔEgap, total hardness (η), electronegativity (χ), electrophilicity index ([Formula: see text]), and the electron transfer fraction from the inhibitor molecule to the copper atom (ΔN) were computed to assess their efficacy in corrosion prevention. The active sites of inhibitors were determined through the analysis of Mulliken charges, highlighting that heteroatoms exhibit the highest electron density and thus serve as key active sites. This observation aligns with Fukui, which indicates that the highest fk+ and fk- correspond to sulfur, nitrogen, and oxygen atoms.