Heteroligand mercury(II) complexes with aspartic,tartaric, and citric acids

Mercury(II) complexes with aspartic (H₂Asp) and tartaric acids (H₂Tart) and heteroligand mercury(II) complexes with H₂Asp, H₂Tart, and citric acids (H₃Cit) were studied by spectrophotometry in aqueous solutions with I = 0.1(NaClO₄) at 20 ± 2°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]^?, HgAsp₂]^2?, HgTart], Hg(OH)Tart]^?, Hg(OH)₂Tart]^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.