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)−NH<sub>3</sub>, M(I)−S<sub>2</sub>O<sub>3</sub><sup>2-</sup>, and M(I)−S<sub>2</sub>O<sub>3</sub><sup>2-</sup>−NH<sub>3</sub> systems (M = Ag, Au) were studied at 25 °C and at <i>I</i> = 0.1 M (NaClO<sub>4</sub>) using a variety of analytical techniques. For the Ag(I)−NH<sub>3</sub>−S<sub>2</sub>O<sub>3</sub><sup>2-</sup> system, AgS<sub>2</sub>O<sub>3</sub>NH<sub>3</sub><sup>-</sup> was detected with formation constant log β<sub>111</sub> (for the reaction Ag<sup>+</sup> + S<sub>2</sub>O<sub>3</sub><sup>2-</sup> + NH<sub>3</sub> ↔ AgS<sub>2</sub>O<sub>3</sub>NH<sub>3</sub><sup>-</sup>) 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 β<sub>101</sub>(AgNH<sub>3</sub><sup>+</sup>), log β<sub>102</sub>(Ag(NH<sub>3</sub>)<sub>2</sub><sup>+</sup>), log β<sub>110</sub>(AgS<sub>2</sub>O<sub>3</sub><sup>-</sup>), and log β<sub>120</sub>(Ag(S<sub>2</sub>O<sub>3</sub>)<sub>2</sub><sup>3-</sup>), obtained from silver potentiometry, were 3.59, 7.0, 8.97, 13.1, respectively. In the case of the ammine complexes, the log β<sub>101</sub>(AgNH<sub>3</sub><sup>+</sup>) and log β<sub>102</sub>(Ag(NH<sub>3</sub>)<sub>2</sub><sup>+</sup>) values were found to be 3.5 and 7.1, respectively, from the UV−vis spectrophotometric experiments. The mixed species AuS<sub>2</sub>O<sub>3</sub>NH<sub>3</sub><sup>-</sup> was detected in UV−vis spectrophotometric, hydrodynamic voltammetric, and potentiometric experiments with the stepwise formation constants (log <i>K</i><sub>111</sub>) of −4.0, −3.5, −3.8, respectively, for the reaction Au(S<sub>2</sub>O<sub>3</sub>)<sub>2</sub><sup>3-</sup> + NH<sub>3</sub> ↔ AuS<sub>2</sub>O<sub>3</sub>NH<sub>3</sub><sup>-</sup> + S<sub>2</sub>O<sub>3</sub><sup>2-</sup>. At higher [NH<sub>3</sub>]/[S<sub>2</sub>O<sub>3</sub><sup>2-</sup>] ratios (>10<sup>5</sup>), the formation of Au(NH<sub>3</sub>)<sub>2</sub><sup>+</sup> was also detected in spectrophotometric and potentiometric experiments with stepwise formation constants (log <i>K</i><sub>102</sub>) of −5.4 and −5.3, respectively, according to the reaction AuS<sub>2</sub>O<sub>3</sub>NH<sub>3</sub><sup>-</sup> + NH<sub>3</sub> ↔ Au(NH<sub>3</sub>)<sub>2</sub><sup>+</sup> + S<sub>2</sub>O<sub>3</sub><sup>2-</sup>.