Ionic Strength Dependence of Formation Constants, Protonation, and Complexation of Nitrilotriacetic Acid with Molybdenum(VI)

Abstract

The complexation of molybdenum(VI) with nitrilotriacetic acid (NTA) has been studied using potentiometric and spectrophotometric techniques. The temperature was kept constant at 25 °C, and the ionic strength was (0.1, 0.5, 0.7, and 1.0) mol dm-3 in NaClO4. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with NTA of the type (MoO3L3-), where L3- represents the fully dissociated NTA anion, at pH 6. The composition of the complex was determined by the continuous variations method. The protonation constants of NTA (using the potentiometric technique) and the stability constant of the complex (using the spectrophotometric technique) were determined at 25 °C and at different ionic strengths. The dependence on ionic strength of the protonation and stability constants was evaluated using a simple Debye−Huckel type equation.