Polymeric thiolate complexes in solution. Stability constants of the cadmium(II) complexes of 4-mercapto-1-methylpiperidine

Abstract

Polynuclear complex formation between Cd^II and 4-mercapto-1-methylpiperidine has been studied by e.m.f. measurements with glass and cadmium amalgam electrodes at 25 °C in a 3 mol dm^–3(sodium) perchlorate medium [+10%(v/v) CH₃OH]. Conclusions drawn from graphical methods agree well with results obtained from the numerical treatment. The best fit to the experimental data corresponds to the existence of two ‘core + links’ series, Cd[Cd(HA)₃]_n^{(2n+ 2)+} and (HA)₂[Cd(HA)₂]_n²ⁿ⁺, HA being the uncharged ligand, from which only the following species are present: [Cd(HA)₄]²⁺(log Ψ_1,4= 23.06 ± 0.01), [Cd₃(HA)₆]⁶⁺(log Ψ_3,6= 48.59 ± 0.02), [Cd₃(HA)₈]⁶⁺(log Ψ_3,8= 61.85 ± 0.03), [Cd₄(HA)₉]⁸⁺(log Ψ_4,9= 73.50 ± 0.02), and [Cd₄(HA)₁₀]⁸⁺(log Ψ_4,10= 80.48 ± 0.01). A mechanism for the formation of these species and their possible geometries are suggested.