Synthesis, structural characterization, DFT computation, and anticorrosive behavior of ethylenediammonium dichloridobis(dihydrogenphosphito)cobaltate(II) on C38 steel in a 1M-HCl solution

Abstract

Under normal conditions, the chemical (C₂H₁₀N₂)[Co(H₂PO₃)₂Cl₂] has been synthesized using the ethylenediamine molecule as a template. Both X-ray diffraction and infrared spectroscopy were used to characterize the title compound. TGA-DTA measurements revealed the thermal stability of the studied complex up to 423 K. The optimal molecular structure and the infrared radiation intensity were determined using density functional theory (DFT/B3LYP) methods with the LanL2DZ basis set; the bands found in the experimental and calculated IR spectra corresponded to the vibrations of the ethylenediammonium cation and the phosphite anion. In addition, boundary molecular orbital (HOMO-LUMO) plots and molecular electrostatic potential (MEP) surfaces are obtained to understand better the electronic properties and reactive sites of chemical species. The calculated structural parameters are in good agreement with the experimental results. Anticorrosive behavior of (C₂H₁₀N₂)[Co(H₂PO₃)₂Cl₂] on C38 steel in 1M-HCl has been studied using the weight loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic dynamic polarization techniques. As the concentration of the studied inhibitor increases, The corrosion rate decreases with increasing inhibitor concentration, enhancing inhibition efficiency. A proposed mechanism suggests that adsorption occurs via electrostatic interactions and coordination bonding, forming a protective barrier that inhibits corrosion.