Thiocyanato and Iodo Complexation of Cadmium(II) Ions in Micellar Solutions of a Nonionic Surfactant Triton X-100

Abstract

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−3NaClO4as 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 that a hydrophobic complex with no capacity to form strong hydrogen bonds in water is favored in micelles.