EXAFS investigations of the mechanism of facilitated ion transfer into a room-temperature ionic liquid

The Sr(II)-crown ether complexes formed in a room-temperature ionic liquid (RTIL), 1-methyl-3-pentylimidazolium bis[(trifluoromethyl)sulfonyl]amide, have been studied by X-ray absorption fine structure measurements at the Sr K-edge. When a Sr(NO(3))(2)-crown ether complex is directly dissolved in a water-saturated RTIL, both nitrate ligands and the crown ether coordinate the Sr, as observed in a conventional two-phase water-octanol system. When the cationic Sr-crown ether complex is created in a two-phase water-RTIL system, however, only cationic Sr-crown ether complexes are observed in the RTIL phase. This difference in the coordination complexes arises from differences in the mechanism of cation extraction between the RTIL and conventional molecular organic solvents, a finding with important implications for synthesis, catalysis, and ion separations using two-phase water-RTIL systems.