Studies on Gold Complexes. II. The Equilibrium between Gold(I) and Gold(III) in the Ammonia System and the Standard Potentials of the Couples Involving Gold, Diamminegold(I), and Tetramminegold(III).

Abstract

The three standard potentials involving gold, gold(I) and gold(III) in the ammonia system are determined in 10 M ammonia nitrate at 25°C by potential measurements with gold and platinium electrodes. The values obtained are: Au(NH3)2^+ + e- <-> Au + 2 NH3 E1,0^0 = +563+- 6mV Au(NH3)4^3+ + 2e- <-> Au(NH3)2 + 2 NH3 E3,0^0 = +206+- 3mV Au(NH3)4^3+ + 3e- <-> Au + 4 NH3 E3,0^0 = +325+- 3mV This leads to an equilibrium constant of 10^-12.1 for the reaction Au(NH3)4^3+ +3e- <-> 3 Au(NH3)2^+ and under certain assumptions to a cumulative stability constant beta2 = 10^26.45 l²/mol² for the amminegold(I) ion.