Probing C–H⋯X hydrogen bonds in amide-functionalized imidazolium salts under high pressure

Abstract

We have probed under high pressure the C-H hydrogen bonds formed by N,N(')-disubstituted imidazolium ions having PF(6) (-) and Br(-) counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N-H...F unit) in the infrared spectrum of the PF(6) (-) salt indicates that conventional N-H...O and N-H...N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C(2)-H...F interactions, combined with other weak hydrogen bonds, disturb the formation of N-H hydrogen bonds in the PF(6) (-) salt. This finding is consistent with the pressure-dependent results, which reveal that the C(2)-H...F interaction is enhanced upon increasing the pressure. In contrast to the PF(6) (-) salt, the imidazolium C-H bonds of the Br(-) salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br(-) and PF(6) (-) ions.

Spectroscopic and Computational Insight into the Intermolecular Interactions between Zwitter‐Type Ionic Liquids and Water Molecules

“…Compared to other geometries of the ZIL-H 2 O systems, the geometries of Figure 1 a and d In recent years, interactions between ILs and water molecules at the molecular level have been studied by computational methods in terms of the energetic aspects of the interactions and the structural and spectroscopic analyses. [15] The types of anions rather than cations and alkyl chain length are reportedly responsible for the interactions with water molecules. [16] In addition, Li et al demonstrated that the strengths of the interactions with water follow the sequence anion > cation > ion pair.…”

“…[15] The types of anions rather than cations and alkyl chain length are reportedly responsible for the interactions with water molecules.…”

Effects of water and methanol on the molecular organization of 1-butyl-3-methylimidazolium tetrafluoroborate as functions of pressure and concentration

“…25 liquids have included the use of x-ray crystallography and vibrational spectroscopy under the condition of ambient pressure. [29][30][31][32] The study of pressure effects reveals the intermolecular interactions of the ionic liquid at a constant kinetic energy or temperature. Although the results of crystal structures are highly informative on the relative geometry changes, crystallography does not provide direct information on the local structure in the liquid state.…”

“…3,[29][30][31][32] It is assumed that the structure of these ionic liquids should be considered as networks of anions and cations, linked together by hydrogen bonds. 3,[29][30][31][32] It is assumed that the structure of these ionic liquids should be considered as networks of anions and cations, linked together by hydrogen bonds.…”

Solid, Solution and Gas Phase Interactions of an Imidazolium-Based Task-Specific Ionic Liquid Derived from Natural Kojic Acid

“…2 Besides ionic interactions, whether supramolecular interactions also govern the organization of imidazoliumbased ILs is still hotly debated with a vast number of important contributions. [24][25][26][27][28][29] Despite their importance, the number of significant contributions specifically discussing the supramolecular organization and interactions of TSILs is much scarcer [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] when compared to nonfunctionalized ILs. TSILs have become one of the most important strategies for furthering IL chemistry, 1 as noted for the large and increasing number of innovative applications described for these ionic compounds.…”