Heteroligand Mercury(II) Complexes with Aspartic, Tartaric, and Citric Acids

Mercury(II) complexes with aspartic (H(2)Asp) and tartaric acids (H-2 Tart) and heteroligand mercury(II) complexes with H-2 Asp, H-2 Tart, and citric acids (H-3 Cit) were studied by spectrophotometry in aqueous solutions with I = 0.1(NaClO4) at 20 +/- 2 degrees C. It was found that the complexation in both binary and ternary systems depends on the concentrations of the reagents and the pH of the medium. The resulting complexes included [HgAsp], [Hg(OH)Asp](-), [HgAsp(2)](2-), [HgTart], [Hg(OH)Tart](-), [Hg(OH)(2)Tart](2-), [HgAspCit](3-), [HgAspTart](2-), and [Hg(OH)AspTart](3-). The logarithms of their stability constants were 11.74 +/- 0.12, 20.18 +/- 0.17, 20.11 +/- 0.10, 5.40 +/- 0.11, 15.52 +/- 0.09, 24.70 +/- 0.12, 19.19 +/- 0.12, 14.55 +/- 0.16 and 23.80 +/- 0.14, respectively. The experimental data were analyzed in terms of the mathematical models that predict the existence of a wide spectrum of complex species in solution and allow one to consider only those species that are sufficient for accurate reproduction of the observed pH-dependence of the optical density.