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

Abstract

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) CH₃OH]. 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)₃]²⁺, [Cd₃(HA)₈]⁶⁺, [Cd₄(HA)₈]⁸⁺, and [Cd₅(HA)₁₂]¹⁰⁺, HA being the uncharged ligand. The deprotonation of these species gives rise to several mono- and poly-nuclear ternary complexes Cd_pA_qH_r, r < q, A denoting the deprotonated form of the ligand. Chelate formation seems very likely. Comparisons with other cadmium(II)–mercaptoamine systems are made.