Study of Complexation Equilibria Between the Iron(III) Ion and 2-Hydroxybenzamide in Aqueous Solution

Abstract

The complexation of the Fe3+ ion with 2-hydroxybenzamide (salicylamide, HL) has been studied, at 25.0 °C, by potentiometric measurements with a glass electrode in 1 mol·dm−3 NaClO4 medium. The concentration of salicylamide (C L) has been varied between (1 × 10−3 and 10 × 10−3) mol·dm−3, while the concentration of metal cation (C M) ranged within (0.5 × 10−3 and 10 × 10−3) mol·dm−3. The ligand to metal concentration ratio has been varied between 1 and 10 and the hydrogen ion concentration was decreased stepwise until the incipient precipitation of a basic salt of the metal, which occurred at different values depending on the specific ligand to metal ratio. The experimental data were consistent with the formation of the complexes FeL2+, Fe(HL)L2+ and $$ {\text{FeL}}_{2}^{ + } $$ . Equilibrium formation constants have been given for the investigated ionic medium as well as for the infinite dilution reference state, evaluated according to the Specific Interaction Theory. The predominant species in neutral solution are $$ {\text{FeL}}_{2}^{ + } $$ and $$ {\text{Fe}}\left( {\text{OH}} \right)_{2}^{ + } $$ .