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

Polynuclear complex formation between CdII 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 Ψ1,4 = 23.06 ± 0.01), [Cd3(HA)6]6+ (log Ψ3,6 = 48.59 ± 0.02), [Cd3(HA)8]6+ (log Ψ3,8 = 61.85 ± 0.03), [Cd4(HA)9]8+ (log Ψ4,9 = 73.50 ± 0.02), and [Cd4(HA)10]8+ (log Ψ4,10 = 80.48 ± 0.01). A mechanism for the formation of these species and their possible geometries are suggested.