Quantum Chemical Modelling and Experimental Validation of Novel Schiff Base Metal Complexes as Anti-Corrosion Coatings for Steel Infrastructure in Nigerian Coastal Environments

Structural steel infrastructure in Nigeria's coastal and offshore environments is subjected to exceptionally aggressive corrosion conditions combining high humidity, chloride aerosol deposition, elevated temperatures, and periodic immersion cycles that drastically shorten service life and demand coatings with superior barrier and active corrosion inhibition performance not provided by conventional zinc-based primers. This study synthesises a series of novel Schiff base ligands derived from the condensation of aromatic amines with salicylaldehyde derivatives, coordinates them with copper(II), zinc(II), and nickel(II) metal ions, and evaluates their performance as active corrosion inhibition components in epoxy-based anticorrosion coatings for mild steel. Quantum chemical calculations at the density functional theory level using the B3LYP/6-311G** basis set predict electronic parameters (HOMO energy, LUMO energy, energy gap, dipole moment, Fukui functions, global hardness, and electron transfer number) that correlate with corrosion inhibition efficiency, guiding lead compound selection prior to synthesis. X-ray crystallography of isolated Schiff base metal complexes establishes crystal structure-property relationships. Corrosion inhibition performance of complexes in solution is characterised by electrochemical methods in simulated coastal seawater. Coating formulations are developed by incorporating optimised complexes into waterborne epoxy binder systems. Coating performance is evaluated by electrochemical impedance spectroscopy, salt spray testing (ASTM B117), cathodic disbondment testing, adhesion testing, and scanning Kelvin probe mapping of delamination fronts under accelerated corrosion conditions representative of Lagos coastal environments. An original structure-performance relationship framework is developed for Schiff base metal complex anticorrosion coatings. Keywords: Schiff base metal complexes, anticorrosion coatings, density functional theory, coastal corrosion, Nigeria