Stability constants for aqueous silver/bromide/thiocyanate complexes

Stability constants for aqueous Ag⁺/Br^?, Ag⁺/SCN^?, and mixed Ag⁺/Br^?/SCN^? complexes are determined at 25° C by using data generated potentiometrically in solutions having ionic strengths of 0.4, 1.0, and 2.0 m. Monte Carlo numerical methods which yield apparent stability constants for these complexes as well as confidence limits are described in detail. Explicit consideration of speciation shows that under useful precipitation conditions (high bromide and low thiocyanate), a significant fraction of soluble silver is present as AgBr_n (SCN)^1?n?m_m complexes. The most prevalent mixed complexes under these conditions are AgBr (SCN)^? (log β₁₁=8.0 ± 0.5) and AgBr₂(SCN)^2? (log β₂₁=9.2 ± 0.3). The free energies of formation of the other tri- and tetra-coordinate mixed complexes are nearly indistinguishable (log β₁₂=9.3 ± 0.5; log β₃₁=9.0 ± 0.6; log β₂₂=9.6 ± 0.9; log β₁₃=10.3 ±0.5).