title: Facilitated transfer of alkali-metal cations by dibenzo-18-crown-6 across the electrochemically polarized interface between an aqueous solution and a hydrophobic room-temperature ionic liquid.
abstract: The facilitated transfer of alkali metal cations (Li+, Na+, K+, Rb+, Cs+) by dibenzo-18-crown-6 (DB18C6) across the electrochemically polarizable interface between an aqueous solution (W) and a hydrophobic ionic liquid, N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([C18Iq][TFPB]), has been studied using cyclic voltammetry at the interface formed at the tip of a micropipet. In cyclic voltammograms (CVs), the current due to the facilitated transfer of the cations by DB18C6 from W to [C18Iq][TFPB] can be measured within the polarized potential window of the [C(18)Iq][TFPB]|W interface. The stoichiometry of the complexes in [C18Iq][TFPB] for Li+, Na+, K+, and Rb+ are found to be 1:1 while for the Cs+ transfer both 1:1 and 1:2 complexes are likely to be formed. The formation constants of the 1:1 complexes for Li+, Na+, K+, and Rb+ in [C18Iq][TFPB], , evaluated from CVs are log = 5.0, 7.0, 8.2, and 7.3, respectively. The value for K+ is 1 order of magnitude greater than that for Na+. This higher selectivity of DB18C6 to K+ over Na+ in [C18Iq][TFPB] compared with that in molecular solvents suggests that the RTIL provides a unique solvation environment for the complexations of DB18C6 with the ions.
authors.affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Nishi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Murakami
authors.forename: Seiichi
authors.initials: S
authors.lastname: Imakura
authors.forename: Takashi
authors.initials: T
authors.lastname: Kakiuchi