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

2004-05-17T00:00:00Z (GMT) by W. Nimal Perera Gamini Senanayake
The M(I)−NH3, M(I)−S2O32-, and M(I)−S2O32-−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−S2O32- system, AgS2O3NH3- was detected with formation constant log β111 (for the reaction Ag+ + S2O32- + 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)23-), 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)23- + NH3 ↔ AuS2O3NH3- + S2O32-. At higher [NH3]/[S2O32-] 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+ + S2O32-.