HSAB descriptors of thiadiazole derivatives calculated by DFT: possible relationship as mild steel corrosion inhibitors
By I. B. Obot, N.O. Obi-Egbedi
The inhibitive effect of some substituted thiadiazoles, 2-amino-1,3,4-thiadiazoles (AT), 2-amino-5-methyl-1,3,4-thiadiazoles (AMT), 2-amino-5-ethyl-1,3,4-thiadiazoles (AET) and 2-amino-5- propyl-1,3,4-thiadiazoles (APT) against the corrosion of mild steel in formic and acetic acid is studied theoretically using DFT at the B3LYP/6-31G(d) level in order to elucidate the different inhibition efficiencies and reactive sites of these compounds as corrosion inhibitors. The calculated quantum chemical parameters correlated to the inhibition efficiency are, EHOMO, ELUMO, energy of the gap (ΔE) and other parameters, including electronegativity ( c ), global hardness (h ), global softness (S) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). The calculated results are in agreement with the experimental data. In addition, the local reactivity has been analyzed through the Fukui function and condensed softness indices as well as Mulliken population analysis.
Keywords : Thiadiazole, corrosion inhibitors, density functional theory (DFT), Fukui function, softness indices