The inhibiting effect of cobalt(III)–cyclam complexes with substituted β-diketones on iron corrosion in perchlorate solution

The inhibiting effect of cobalt(III) complexes with macrocyclic ligand cyclam (1,4,8,11-tetraazacyclotetradecane) and β-diketonato ligands have been investigated on iron corrosion in 0.1 M HClO 4 by potentiodynamic, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements. Analysis of the polarization curves and impedance spectra, by adding complex compounds to the acid solution and comparing with inhibitor-free solution, show corrosion current decrease and charge transfer resistance increase, respectively. Impedance data are fitted with equivalent circuit models. The stability of the adsorbed film was followed by LPR. Scanning electron microscopy (SEM) was used to screen physical changes of the reacted surfaces both treated and untreated. The differences in inhibitor efficiencies depend on the substituent group of the coordinated β-diketone ligand. Structural and electronic properties of this group of compounds in relation to inhibitor efficiency were analyzed by using the molecular modeling structures and correlated with previously reported spectroscopy data.