Gold(III) amine complexes in aqueous alkali solutions

The gold(III) 1,3-diaminopropane complex Au(1,3-pn)(1,3-pn-H)]Cl₂ has been synthesized. Its dissociation constant has been determined: Au(1,3-pn)₂³⁺ = Au(1,3-pn-H)²⁺ + H⁺, logK _a1 = −7.03 ± 0.05 (I = 0.1 mol/L NaClO₄). Considerable spectral changes are observed for strong alkali solutions (pH 11–14) containing the monoamido forms of the gold(III) ethylenediamine, 1,3-diaminopropane, and diethylenetriamine complexes (Au(en)(en-H)²⁺, Au(1,3-pn)(1,3-pn-H)²⁺, Au(dien-H)OH⁺). These changes are attributed to the formation of the diamido species Au(en-H)₂⁺, Au(1,3-pn-H)₂⁺, and Au(dien-2H)OH⁰. The dissociation constants of the monoamido complexes have been determined: Au(en)(en-H)²⁺ (logK _a2 = −10.9 ± 0.1 at I = 0.001–0.01 mol/L NaCl); Au(1,3-pn)(1,3-pn-H)²⁺ (logK _a2 = −11.3 ± 0.1 at I = 0.1 mol/L NaCl); Au(dien-H)OH⁺ (logK _a2 = −12.4 ± 0.1 at I = 0.1 mol/L NaCl).