Stability and spectral characteristics of the U(VI)-alizarin maroon-thiosalicylic acid ternary complex

Abstract

The stability constant of the ternary U(VI) complex containing alizarin maroon (azm) and, as a second ligand, thiosalicylic acid (tsa) in a 1 : 1 : 1 molar ratio was determined by potentiometric titration in 40% (v/v) ethanol-water medium [ I = 100 mmol dm −3 (NaClO 4), 25 ± 0.1°C]. For the equilibrium, U(azm) 2 + U(tsa) 2 ⇌ 2U (azm)(tsa), the corresponding constant, log X, was found to be 2.80 (0.27). The constant given in parentheses is due to Δ log K = log K U(tsa) U(azm)(tsa) −log K U U(azm). The absorption spectra of the U(azm)(tsa) ternary complex were investigated and a sensitive method was developed for the microdetermination of uranium based on the formation of this complex. The solution spectrum of the ternary complex gave an absorption band at 630 nm over the pH range 5.8–7.4. The ternary system conformed Beer's law between 5.9 and 66.6 μg cm −3 uranium with a molar absorptivity of 2 × 10 4 l mol −1 cm −1. The IR spectra of the mono- and biligand complexes were also studied.