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

•The crystal structure of ([DEME][I]) was characterized by a single-crystal X-ray diffraction.•We found that two crystallographically unequivalent molecules exist in the unit cell.•The G−G−–g−g−t and G+G+–g+g+t conformers of [DEME] cation exist in the single-crystalline state.•We further discussed the conformational preferences of [DEME][I] in the liquid states.

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.

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