Interfacial ion pairing at the interface between water and a room-temperature ionic liquid, N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide

The specific interaction of N-tetradecylisoquinolinium (C ₁₄Iq⁺) with Cl^- and Br^- has been detected in the voltammetry of ion transfer and electrocapillarity at the interface between an aqueous solution (W) and a room-temperature ionic liquid (RTIL), N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide ([C ₁₄Iq⁺][C₂C₂N^-]). This specific interaction also makes the transfer of Cl^- and Br ^- into [C₁₄lq⁺][C₂C ₂N^-] energetically more favorable in comparison with that of F^- and SO₄^2-. The width of the polarized potential window in ion-transfer voltammetry at the [C₁₄Iq ⁺][C₂C₂N^-]|W interface is significantly narrower because of the transfer of anions from W to RTIL. The degree of affinity of the anion with C₁₄Iq⁺ agrees with the Hofmeister series. Such an ion-pair formation of anions in W wth cations in the RTIL is much weaker when the cation constituting the RTIL is a symmetric tetraheptylammonium ion.