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The fab four: Far-infrared difference spectra and DFT-calculated properties for mixtures of protic ionic liquids (PILs) and water clearly indicate that a minimum of four water molecules are needed to transfer contact (CIPs) into solvent-separated (SIPs) ion pairs. SIPs are favored over CIPs owing to additional H-bonds and cooperative effects. This enthalpic advantage overcompensates for the entropic penalty of separation by water.
Stange et al. (Sun,) studied this question.