Synthesis, Characterization, and Corrosion Inhibition Assessment of Three New Mononuclear Hybrid Complexes Based on Schiff (2-(2-Hydroxybenzylidene)amino)phenol and Triphenylphosphine Ligand

In this study, we describe the synthesis and characterization of the mononuclear complexes [CuL(P(Ph)3)]2+, [NiL(P(Ph)3)Cl2], and [CoL(P(Ph)3)Cl2], where L = (2-((2-hydroxybenzylidene)amino)phenol). The structural analysis of these complexes was carried out utilizing mass spectrometry, 1H NMR, 13C NMR, 31P NMR, UV–visible, and FT-IR. All three complexes were investigated as corrosion inhibitors for mild steel in 1 M HCl. Stationary and transient electrochemical methods were used to evaluate their anticorrosion performance. In addition, the comparison of the three representation planes (Nyquist, Bode, and Betova) guided us in selecting the appropriate equivalent electrical circuit. Furthermore, we have highlighted the disadvantages of processing data from the anodic branch of polarization curves, as well as the limitations of modeling the electrochemical interface with a simple circuit featuring a single time constant when processing electrochemical impedance spectra. Scanning electron microscopy was also used to evaluate the morphological characteristics of metal surfaces. All these investigative techniques showed good agreement, and the results obtained in terms of resistance were as follows: [CuL(P(Ph)3)]2+ > [NiL(P(Ph)3)Cl2] > [CoL(P(Ph)3)Cl2] > L, when compared to the uninhibited solution of 1 M HCl alone. SEM, EDX, and UV–visible techniques were also used for surface morphology studies in both inhibited and uninhibited systems. Using density functional theory (DFT) and molecular dynamics (MD) simulations, the aqueous adsorption orientation of the Schiff base molecule and the three complexes on a mild steel surface was examined. The quantum theory of atoms in molecules (QTAIM) was used to examine the types of bonds that exist between the core metal ions and ligands.