Gold(III) Chlorohydroxo Complexes in Aqueous Solutions at Increased Temperatures

The stagewise substitution equilibria AuCl^- ₄ + iOH^– = AuCl_{4 – i} OH_i ^- + iCl^–, β_i in aqueous solutions at 50 and 80°C (I = 1 mol/L NaCl) have been studied. The equilibrium constants log β₁ = 7.26, log β₂ = 13.98, log β₃ = 19.66, log β₄ = 24.78 (50°C); log β₁ = 6.89, log β₂ = 13.13, log β₃ = 18.43, and log β₄ = 23.30 (80°C) have been determined. They are lower than the same constants at 25°C. The spectra of complex speciesspecies at 80°C have been calculated, and the heterogeneous equilibrium 0.5Au₂O₃ xH₂O_S + OH^– = Au(OH)₄ ^- + 0.5xH₂O of the red Au₂O₃ · xH₂O_S species at 80°C has been studied, logK_S = 3.7 ± 0.2. The obtained results may be useful in geochemistry and the synthesis of gold nanoparticles.