Polymeric thiolate complexes in solution. Stability constants of the cadmium(II) complexes of 3-aminopropane-1-thiol

Complex formation between Cd^II and 3-aminopropane-1-thiol has been studied by means of nearly 425 e.m.f. measurements with a glass electrode in 10 separate titrations at 25 °C in 3 mol dm^-3 (sodium) perchlorate medium [+10%(v/v) CH<inf>3</inf>OH]. Conclusions drawn from graphical methods based on the 'core + links' hypothesis and on the 'extended variation' technique are in accord with results obtained from the numerical treatment. Experimental data for 3< -log [H⁺] < 11 can be explained by assuming that the following complexes predominate over a wide pH range: [Cd(HA)<inf>3</inf>]²⁺, [Cd<inf>3</inf>(HA)<inf>8</inf>]⁶⁺, [Cd<inf>4</inf>(HA)<inf>8</inf>]⁸⁺, and [Cd<inf>5</inf>(HA)<inf>12</inf>]¹⁰⁺, HA being the uncharged ligand. The deprotonation of these species gives rise to several mono- and poly-nuclear ternary complexes Cd<inf>p</inf>A<inf>q</inf>H<inf>r</inf>, r < q, A denoting the deprotonated form of the ligand. Chelate formation seems very likely. Comparisons with other cadmium(II)-mercaptoamine systems are made.