Integrated spectroscopic and computational assessment of a new Co(II) Schiff base complex as an anticorrosive and in vitro cytotoxic activities

This study examines the corrosion inhibition of carbon steel (CS) in 1.0 M HCl using a newly synthesized dimetallic Co(II) Schiff base complex, [Co 2 (H 2 L)(NO 3 ) 2 (H 2 O) 4 ].3.5H 2 O, where H 4 L (DPD) is an amino acid Schiff base derived from 4,6-diacetylresorcinol and alanine. The Co-DPD complex was characterized by elemental analysis, UV–Vis, FTIR, mass spectrometry, thermal analysis, molar conductivity, and magnetic susceptibility measurements. The results showed that DPD behaves as a bis (monoanionic tridentate) ligand, while conductivity measurements confirmed the neutral nature of the complex and spectral data supported an octahedral geometry. Corrosion inhibition performance was evaluated using weight-loss, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) over the concentration range 10⁻⁶-10⁻ 2 M and temperature range 298–338 K. The inhibition efficiency followed the order Co-DPD > DPD. PDP results indicated mixed-type inhibition, whereas EIS confirmed the formation of a compact protective film. Thermodynamic parameters, including positive ΔH* and negative ΔS*, suggested an adsorption-controlled process. Adsorption obeyed the Langmuir isotherm model. Surface analyses by SEM, EDX, AFM, FTIR, XRD, and contact angle measurements confirmed effective surface shielding. In addition, Co-DPD exhibited promising cytotoxic activity against HepG-2 cells (IC 50 = 9.91 µg/mL). DFT, molecular docking, and Monte Carlo simulations further supported the strong adsorption and high protective performance of Co-DPD.