Structural Consequences of Halogen Bonding in Dialkylimidazolium: A New Design Strategy for Ionic Liquids Illustrated with the I2Cocrystal and Acetonitrile Solvate of 1,3-Dimethylimidazolium Iodide

The reaction of 1,3-dimethylimidazolium-2-carboxylate with elemental iodine in acetonitrile rapidly affords crystalline iodide salts of the 1,3-dimethyl-2-iodoimidazolium cation ([C1mim-2-I]+), [C1mim-2-I]I·0.5I2, and [C1mim-2-I]I·0.5CH3CN, depending on the temperature. Analysis of the two structures shows the significant role of halogen bonding interactions between the cation and anion in the [C1mim-2-I]I salts, which reduces the ionicity of the compounds. This observation is backed by theoretical calculations revealing the importance of halogen bonding as a design strategy for ionic liquids (ILs), which, so far, has been underestimated. The halogen bonding is also analyzed in terms of this new design concept for ILs.