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A Theoretical Investigation of the Interactions between Water Molecules and Ionic Liquids

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journal contribution
posted on 07.12.2006, 00:00 by Yong Wang, Haoran Li, Shijun Han
Quantum chemical calculations have been used to investigate the interaction between water molecules and ionic liquids based on the imidazolium cation with the anions [Cl-], [Br-], [BF4-], and [PF6-]. The predicted geometries and interaction energies implied that the water molecules interact with the Cl-, Br-, and BF4- anions to form X-···W (X = Cl or Br, W = H2O), 2X-···2W, BF4-···W, and W···BF4-···W complexes. The hydrophobic PF6- anion could not form a stable complex with the water molecules at the density functional theory (DFT) level. Further studies indicate that the cation could also form a strong interaction with the water molecules. The 1-ethyl-3-methylimidazolium cation (Emim+) has been used as a model cation to investigate the interaction between a water molecule and a cation. In addition, the interaction between the ion pairs and the water was studied by using 1-ethyl-3-methylimidazolium chloride (Emim·Cl) as a model ionic liquid. The strengths of the interactions in these categories follow the trend anion−W > cation−W > ion pair−W.

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