Ion Speciation of Protic Ionic Liquids in Water: Transition from Contact to Solvent-Separated Ion Pairs

摘要

Ionic liquids (ILs) are receiving increasing amount of interest because of their potential applications, including novel synthesis, electrolyte devices, photochemical cells, separation, and catalysis.One of the important features affecting the properties of ionic liquids is ion pair formation. Ion pairing in solution is the result of a subtle balance between ion-solvent interaction and cation-anion interaction. This is in particular true for ionic liquids where a mix of Coulomb forces, hydrogen bonds, and dispersion forces between the cation and anion leads to unique macroscopic properties of these Coulomb fluids. If the anion-cation interaction is sufficiently strong, contact ion pairs (CIPs) are the dominant structures in the mixtures. If the ion-solvent interaction is stronger, solvent-shared and solvent-separated ion pairs (SIPs) prevail.