Structural and conformational properties of the quaternary ammonium ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium iodide

We have used single-crystal X-ray structural analysis and Raman spectroscopy to study the crystalline structure and conformational properties of a quaternary ammonium ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium iodide ([DEME][I]). At 296 K the crystal structure of [DEME][I] was determined to be monoclinic (P21/a, Z = 8) with a = 13.216 (5), b = 12.842 (3), c = 14.417 (6), β = 104.10 (3)°, and V = 2373.1 (15) Å3. With results from X-ray diffraction measurements and density functional theory calculations, we have identified two folded forms: Gauche−-Gauche−–gauche−-gauche−-trans and Gauche+-Gauche+–gauche+-gauche+-trans conformers, having intramolecular attractive N+⋯O− interactions of [DEME]+ in the single-crystal state. In the liquid state, [DEME]+ exists in equilibrium between folded and (non-interacting) extended forms.