Thiocyanato and iodo ccmplexation of cadmium(II) ions in micellar solutions of a nonionic surfactant Triton X-100

Complexation of the cadmium(II) ion with thiocyanate and iodide ions have been studied by precise titration calorimetry in micellar solutions of a nonionic surfactant Triton X-100 containing 0.4 mol dm(-3) NaClO4 as a constant ionic medium at 298 K. With regard to the Cd(II)-SCN- system, the formation of [Cd(NCS)](+) and [Cd(NCS)(SCN)] in aqueous solution and [Cd(NCN)(2)(SCN)](-) in micelles was established, though the complexation in micelles is not extensive. With the Cd(II)-I- system, the formation of [CdI](+), [CdI3](-), and [CdI4](2-) was established in aqueous solution together with the formation of [CdI2], [CdI3], and [CdI4](2-) in micelles. It is revealed that the complexation in micelles is accompanied by relatively large and negative enthalpies, which is ascribed to the enthalpies of transfer of [CdI3](-) and [CdI4](2-) from aqueous solution to micelles. This suggests th at a hydrophobic complex with no capacity to form strong hydrogen bonds in water is favored in micelles. (C) 1997 Academic Press.