title: Formation of Copper(II) Thiocyanato and Cadmium(II) Iodo Complexes in Micelles of Nonionic Surfactants with Varying Poly(ethylene oxide) Chain Lengths.
abstract: Formation of copper(II) thiocyanato and cadminum(II) iodo complexes in micelles of poly(ethylene oxide) (PEO)-type nonionic surfactants with varying PEO chain lengths of 9.5 (Triton X-100), 30 (Triton X-305), and 40 (Triton X-405) has been studied by titration spectrophotometry and calorimetry at 298 K. In a given surfactant solution, all data obtained were analyzed by assuming formation of ternary complexes MX(n)Y(m)((2-n)+) (M = Cu(II),Cd(II); X = SCN(-), I(-); Y = surfactant), and the complexes thus form in aqueous phase (m = 0) or in micelles (m = 1). In the Cu(II)-SCN(-) system, spectrophotometric data obtained by varying concentrations of the surfactant can be explained well in terms of formation of Cu(NCS)(2)Y in micelles and Cu(NCS)(+) and Cu(NCS)(2) in an aqueous phase, and it turned out that formation constant of Cu(NCS)(2)Y increases with increasing PEO chain length. In the Cd(II)-I(-) system, the formation of CdI(3)Y(-) and CdI(4)Y(2-) is concluded in micelles, and that of CdI(+), CdI(3)(-), and CdI(4)(2-) in an aqueous phase. Interestingly, formation enthalpies of CdI(3)Y(-) and CdI(4)Y(2-) become significantly less negative with increasing PEO chain length. This suggests that transfer of the complexes from aqueous solution to a hydrophobic octylphenyl (OP) moiety in micelles is significantly more exothermic than that to a hydrophilic PEO one. Thermodynamic parameters of transfer of CdI(3)(-) and CdI(4)(2-) from aqueous solution to the OP and PEO moieties of micelles have been evaluated. Copyright 2000 Academic Press.
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
authors.initials: M
authors.lastname: Shin
authors.initials: Y
authors.lastname: Umebayashi
authors.initials: R
authors.lastname: Kanzaki
authors.initials: Si
authors.lastname: Ishiguro