DFT computational study of pyridazine derivatives as corrosion inhibitors for mild steel in acidic media

The molecular structures of two Pyridazine derivative;5-phenyl-6-ethyl-pyridazine-3-thione (PEPT) and 5-phenyl-6-ethylpridazine-3-one (PEPO) were simulated for corrosion inhibition efficiency using quantum chemical calculations based on density functional theory (DFT) at the B3LYP/6-31G* basis set level in order to compare the relationship between their molecular structure,electronic structure and inhibition potential.The quantum chemical properties for inhibition efficiency such as EHOMO (energy of the highest occupied molecular orbital), ELUMO (energy of the lowest unoccupied molecular orbital), energy gap (ΔE), dipole moment (μ), global hardness (η), global softness (S), electronegativity (χ), electrophilicity (ω), nucleophilicity (ɛ), electrons transferred from inhibitors to metal surface (ΔN), and the energy change during electronic back-donation process (ΔE*) were calculated. The results show that 5-phenyl-6-ethyl-pyridazine-3-thione (PEPT) would have higher inhibition efficiency than 5-phenyl-6-ethylpridazine-3-one (PEPO) due to its relative EHOMO, ELUMO, ΔE, μ, η, S , ꭓ, ω, ΔN, and ∆E*.