Intermolecular hydrogen bonds in water@IL supramolecular complexes

The role of small amounts of water in ionic liquids (ILs), namely, 1-n-butyl-2,3-dimethylimidazolium imidazolate (BMMI·Im), 2-methylimidazolate (BMMI·MeIm), and pyrazolate (BMMI·Pyr), is examined using NMR spectroscopy and density functional theory (DFT) calculations. The nuclear Overhauser effect (NOE) indicates that a water molecule is trapped inside the ionic network, keeping the ion pair in contact through strong H-bonds involving the hydrogen atoms of water and the nitrogen atoms of the IL anions to give a guest@host supramolecular structure. The formation of the H2O@IL pair complex with different ILs combined with the strong hydrogen bond strength within the complex is responsible for the selective H/D exchange reactions at the imidazolium C2-Me and ketone Cα positions.