The Ammine, Thiosulfato, and Mixed Ammine/Thiosulfato Complexes of Silver(I) and Gold(I)

The M(I)−NH₃, M(I)−S₂O₃^2-, and M(I)−S₂O₃^2-−NH₃ systems (M = Ag, Au) were studied at 25 °C and at I = 0.1 M (NaClO₄) using a variety of analytical techniques. For the Ag(I)−NH₃−S₂O₃^2- system, AgS₂O₃NH₃^- was detected with formation constant log β₁₁₁ (for the reaction Ag⁺ + S₂O₃^2- + NH₃ ↔ AgS₂O₃NH₃^-) of 11.2, 10.4, and 10.8 on the basis of silver potentiometry, UV−vis spectrophotometry, and hydrodynamic voltammetry, respectively. Also, the values of log β₁₀₁(AgNH₃⁺), log β₁₀₂(Ag(NH₃)₂⁺), log β₁₁₀(AgS₂O₃^-), and log β₁₂₀(Ag(S₂O₃)₂^3-), obtained from silver potentiometry, were 3.59, 7.0, 8.97, 13.1, respectively. In the case of the ammine complexes, the log β₁₀₁(AgNH₃⁺) and log β₁₀₂(Ag(NH₃)₂⁺) values were found to be 3.5 and 7.1, respectively, from the UV−vis spectrophotometric experiments. The mixed species AuS₂O₃NH₃^- was detected in UV−vis spectrophotometric, hydrodynamic voltammetric, and potentiometric experiments with the stepwise formation constants (log K₁₁₁) of −4.0, −3.5, −3.8, respectively, for the reaction Au(S₂O₃)₂^3- + NH₃ ↔ AuS₂O₃NH₃^- + S₂O₃^2-. At higher [NH₃]/[S₂O₃^2-] ratios (>10⁵), the formation of Au(NH₃)₂⁺ was also detected in spectrophotometric and potentiometric experiments with stepwise formation constants (log K₁₀₂) of −5.4 and −5.3, respectively, according to the reaction AuS₂O₃NH₃^- + NH₃ ↔ Au(NH₃)₂⁺ + S₂O₃^2-.