Anion Dependent Dynamics and Water Solubility Explained by Hydrogen Bonding Interactions in Mixtures of Water and Aprotic Heterocyclic Anion Ionic Liquids.

Molecular dynamics simulations were used to compare water solubilities and the effects of water on the structure and dynamics of ionic liquids (ILs) composed of phosphonium cations paired with azolide and phenolate anions. The addition of water decreases ordering of the ions compared to the dry ILs with the exception of anion-anion ordering in the phenolate IL. The result is that the dynamics of the azolide ionic liquids increase significantly upon addition of water, whereas the phenolate IL dynamics show little change. The relative water solubilities were compared through calculation of Henry's law constants. Water is much more soluble in the phenolate IL due to strong hydrogen bonding interactions between water and the phenolate oxygen atom. Anions can therefore be selected to control IL-water hydrogen bonding for optimal performance in applications such as CO2 separation.