Additional Aspects of Complexation of Gold(I) with Thiomalate

Some equilibria involving gold(I) thiomalate (mercaptosuccinate, TM) complexes have been studied in the aqueous solution at 25 °C and I = 0.2 mol·L⁻¹ (NaCl). In the acidic region, the oxidation of TM by (Formula presented.) proceeds with the formation of sulfinic acid, and gold(III) is reduced to gold(I). The interaction of gold(I) with TM at n_TM/n_Au ≤ 1 leads to the formation of highly stable cyclic polymeric complexes (Formula presented.) with various degrees of protonation depending on pH. In general, the results agree with the tetrameric form of this complex proposed in the literature. At n_TM/n_Au > 1, the processes of opening the cyclic structure, depolymerization and the formation of (Formula presented.) occur: (Formula presented.), log₁₀K₄₅ = 10.1 ± 0.5; 0.25 (Formula presented.), log₁₀K₁₂ = 4.9 ± 0.2. The standard potential of (Formula presented.) is (Formula presented.). The numerous protonation processes of complexes at pH < 7 were described with the use of effective functions.