About the stability of Au(NH3) 4 3+ in aqueous solution

The transformations of Au(OH) ₄ ^? in aqueous solutions (T = 20°C, I = 1) containing NH₃ and NH ₄ ⁺ (pH 8.1–8.5) were studied. The most pronounced changes in the system occur in the range 0 > log NH ₄ ⁺ ] > ?2.0 (c _Au = (1?10) × 10^?4 mol/L, the monitoring time was about two weeks). When log NH ₄ ⁺ ] > 0, Au(NH₃) ₄ ³⁺ dominates together with the amido form Au(NH₃)₃NH ₂ ²⁺ ; when log NH ₄ ⁺ ] < ?2.0, no changes in the spectra are observed, probably, because of the very low rate of the processes. As c _Au increases in the indicated range, the polymerization rate grows. The equilibrium constant for Au(NH₃)₃OH²⁺ + NH₃ = Au(NH₃) ₄ ³⁺ + OH is log $ K_{4 OH, NH_3 } The transformations of Au(OH)₄⁻ in aqueous solutions (T = 20°C, I = 1) containing NH₃ and NH₄⁺ (pH 8.1–8.5) were studied. The most pronounced changes in the system occur in the range 0 > log NH₄⁺] > −2.0 (c _Au = (1−10) × 10⁻⁴ mol/L, the monitoring time was about two weeks). When log NH₄⁺] > 0, Au(NH₃)₄³⁺ dominates together with the amido form Au(NH₃)₃NH₂²⁺; when log NH₄⁺] < −2.0, no changes in the spectra are observed, probably, because of the very low rate of the processes. As c _Au increases in the indicated range, the polymerization rate grows. The equilibrium constant for Au(NH₃)₃OH²⁺ + NH₃ = Au(NH₃)₄³⁺ + OH is log = −4.2 ± 0.3. This constant was used together with other constants, taking into account possible ligand effects, to estimate the formation constant of Au(NH₃)₄³⁺: logβ₄ = 47 ± 1, E _3/0 = 0.64 ± 0.02 V, log = −8.5 ± 1 (substitution of 4 NH₃ for 4 OH⁻ in Au(OH)₄⁻), log = 17.5 ± 1 (substitution of 4NH₃ for 4Cl⁻ in AuCl₄⁻). Original Russian Text ? I.V. Mironov, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 4, pp. 711–715.