A study of solvent effects on complex formation of tungsten(VI) with ethylenediaminediacetic acid in aqueous solutions of propanol

Abstract

By using spectrophotometric and potentiometric techniques, the formation constants of the species formed in the systems H⁺+W(VI) + ethylenediaminediacetic acid and H⁺ + ethylenediaminediacetic acid were determined in aqueous solutions of propanol at 25°C and a constant ionic strength of 0.1 mol dm⁻³ sodium perchlorate. The composition of the complex was determined by the continuous variation method. It was shown that tungsten(VI) formed a mononuclear 1: 1 complex with ethylenediaminediacetic acid of the type WO₃L³⁻ at −log[H⁺] = 5.8. The formation constants in various media were analyzed in terms of the Kamlet-Taft parameters. Solvents were parameterized by dipolarity/polarizability scales π*, hydrogen-bond donor (HBD) strength α, and hydrogen-bond acceptor strength β. Linear dependences (LSERs) on these solvent parameters were used to correlate and predict a wide variety of solvent effects and provide an analysis of them. Linear relationships were observed when log K_S values were plotted versus π*. Finally, the results are discussed in terms of the effect of solvents on complex formation.