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The present work deals with the synthesis of two new heterocyclic Schiff bases, namely 4,4’-bis(3-thienylidéneimino) biphenyl (HL1) and 4,4’-bis(2-furylidéneimino) biphenyl (HL2), by condensing 4,4'-diaminobiphenyl with 3-carboxaldehyde thiophene and 2-carbaxaldehyde furan, respectively. The obtained compounds were characterized by different spectroscopic techniques. The corrosion inhibition properties of the investigated Schiff bases were evaluated for mild steel in 1M HCl medium, using weight loss measurement, potentiodynamic polarization and impedance spectroscopy. All the measurements showed that the inhibition efficiency increases with the increase in the inhibitor’s concentrations. Furthermore, the experimental results were confirmed by the quantum chemical calculations using the density functional theory (DFT). The different proprieties for each compound have been analyzed by means of the HOMO-LUMO to determine the energy gap (∆E), Electron affinity (EA), Ionization potential (I), Global Electrophilicity (ω), Global Hardness (η)and Chemical Potential (µ). The fraction of electrons transferred (ΔN) and the total energy (TE) were also calculated. The local selectivity and reactivity have been analyzed through the Fukui function in order to compare the possible sites for nucleophilic and electrophilic attacks. The polarization curves studies showed that both tested compounds are mixed-type inhibitors. The DFT investigation is in good accordance with the experimental results.

An examination was conducted on a newly developed compound named N1-(coumarin-7-yl) amidrazone (Azo-Cum) to assess its impact on the corrosion of mild steel (MS) in a 1 M hydrochloric acid (HCl) solution. Various analytical techniques, including weight loss, potentiodynamic polarization (PDP), impedance spectroscopy (EIS), cyclic voltammetry (CV), UV–visible spectroscopy, scanning electron microscopy (SEM), and AFM, were employed to evaluate the inhibitory efficiency of the compound. The findings indicated that inhibition efficiency rose with higher concentrations but decreased with elevated temperatures. According to weight loss analysis, the optimal concentration of the new eco-friendly inhibitor (5 ×10−4M) exhibited a maximum efficiency of 89.26%. Polarization studies disclosed that Azo-Cum acted as a mixed-type inhibitor with a cathodic predominance. The adsorption of the inhibitor on the MS surface followed the Langmuir adsorption isotherm. Additionally, the study explored the synergistic effect of Azo-Cum in combination with KI on MS corrosion in a 1 M HCl (Blank) solution using potentiodynamic polarization measurements. The results identified concentration ranges that demonstrated antagonistic inhibition. Density functional theory (DFT) and molecular dynamic simulation (MD) calculations were performed to investigate the correlation between molecular and chemical reactivity.