Synthesis, characterization and corrosion inhibition in acid medium of l -histidine Schiff base complexes

Abstract

Complexes of cobalt(II), nickel(II) and copper(II) of l-histidine Schiff base derived from 2,4-dihydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde have been synthesized. The structures of ligands and complexes have been characterized using elemental analysis, molar conductance, magnetic moment measurements, and spectral and thermal studies. The ligands behave as tridentate, coordinating through the azomethine nitrogen and α-hydroxyl and carboxylic oxygen atoms. The obtained results show that the Cu(II) complexes have square planar geometry, the Co(II) complexes have octahedral and tetrahedral geometries and the Ni(II) complexes have square planar and octahedral geometries. The molecular geometries of the metal complexes are supported by three-dimensional molecular modelling using molecular mechanics (MM+) and semiempirical molecular orbital calculations (PM3). The inhibition effect of ligands and complexes on the corrosion of aluminium in 2 M H2SO4 was investigated using weight loss. The inhibition efficiency is found to increase with increasing inhibitor concentration and temperature. The increase in inhibition efficiency with increasing temperature is suggestive of a chemical adsorption process.