Targeted synthesis of two iron(III) tetradentate dibasic chelating Schiff base complexes toward inhibition of acidic induced steel corrosion: Empirical and DFT insights

Two new azomethine chelates for Fe3+ ions were prepared from two dibasic tetradentate chelating imine ligands. The studied Schiff base ligands were 2,2 '-((1E,1 ' E)-((4-nitro-1,2-phenylene)bis(azanylylidene))bis(methanylylidene))bis(4-bromophenol) (NABS) and 2,2 '-((1E,1 ' E)-((4,5-dimethyl-1,2-phenylene)bis(azanylylidene))bis(methanylylidene))bis(4-bromophenol) (MABS). Alternative spectral and physicochemical tools such as Fourier transform infrared spectroscopy (FTIR), C-13 NMR, H-1 NMR, and CHN analyses, thermogravimetric analysis (TGA), molecular electronic spectra, and magnetic susceptibility measurements were applied to inspect the structural composition of the compounds under investigation. In addition, the DFT approach was used to optimize the geometry of all compounds in order to get ideal structures and important characteristics. The synthesized compounds examined as an anticorrosive films of C-steel in acidic chloride medium utilizing theoretical and electrochemical studies such electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and potentiodynamic anodic polarization curve (PAP) approaches. The inhibition efficiency augmented with the increasing of the inhibitor dose. The prepared Schiff bases and their iron complexes exhibited protection capacity around 96.8% in the presence of 0.5 mmol L-1. PDP outcomes approve the additive molecules act as mixed inhibitors. The Langmuir model is followed by Schiff bases and their iron complexes as it is contains both chemical and physical adsorption on the metal interface. The surface morphology of the substrate (in blank and inhibited systems) was scanned using field-emission scanning electron microscopy (FESEM). A good agreement among experimental techniques and corresponding density functional theory (DFT) results was found, which confirmed the purity of the studied compounds and suggested octahedral geometry around Fe(III) ions in both MABSFe and NABSFe complexes.