SPECTROSCOPIC DETERMINATION OF THE STOICHIOMETRIES AND STABILITY CONSTANTS OF IRON (III) AND ALUMINIUM (III) COMPLEXES OF SALICYLIC ACID

Abstract

The salicylic acid complexes of iron (III) and aluminium (III) ions have been studied using Job’s continuous variation and Yoe-Jone’s molar ratio methods. The equilibrium constants, K, of the reactions have been determined, and the stoichiometries of the complexes were determined to be 1:1 metal: ligand. The λmaxfor Fe/Sal+ and Al/Sal+ complexes were determined to be at 530 nm and 315 nm respectively. The log K and free energy (∆G) of the formation of FeSal+ were evaluated to be 7.31 and – 41.71 kJ mol-1 respectively, while those of AlSal+ were 5.93 and -33.84 kJ mol-1. The pH for the maximum formation of FeSal+ and AlSal+ complexes were found to be in the range 2.4 to 3.0 and 2.8 to 4.0 respectively. Experimental data suggest that salicylic acid formed a more stable complex with Fe(III) ion than with Al(III) ion. Key words: Stability constant, stoichiometry, coordination complexes, salicylic acid, chelation therapy.