Evidence for spin diffusion in a H,H‐NOESY study of imidazolium tetrafluoroborate ionic liquids

Abstract

The ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-methyl-3-propylimidazolium tetrafluoroborate ([PMIM][BF4]) were studied by H,H-NOESY NMR using a cross-relaxation matrix analysis. Cross-peak intensities are seen to increase with increasing mixing time. Experimental and theoretical hydrogen-hydrogen distances are in agreement at short mixing times (50 ms). Mixing times longer than 50 ms result in an increasing contribution of spin diffusion that produces unrealistically short hydrogen-hydrogen distances. Gas-phase ab initio molecular structures are obtained using Hartree-Fock (HF) and density functional theory (B3LYP) methods at the 6311 + G(2d,p) basis set level. The hydrogen-hydrogen distances obtained from the theoretical structures are in reasonable agreement with those calculated from the cross-relaxation matrices.

Raman Spectroscopy and Ab-Initio Model Calculations on Ionic Liquids

“…These results are consistent with the observation of both conformers being simultaneously present in the spectra of the [C 4 mim] þ cation liquids are given in Fig. 13 and the assignments are specified in Table 2, based on the calculations, some of which are summarized in [132][133][134][135][136].…”

Nuclear magnetic resonance spectroscopic studies of the trihexyl (tetradecyl) phosphonium chloride ionic liquid mixtures with water

“…Other NMR studies of this family of ionic liquids and their mixture with molecular solvents support the occurrence of hydrogen bonding between the imidazolium alkyl groups and the anions [10][11][12][13][14][15]. Among mixtures of ionic liquids with molecular solvents, those with water are especially important as the presence of water in ionic liquids may affect their solvent properties [16][17].…”

“…Among mixtures of ionic liquids with molecular solvents, those with water are especially important as the presence of water in ionic liquids may affect their solvent properties [16][17]. To our knowledge, there is no NMR data on mixtures of water and phosphonium ionic liquids, despite extensive NMR studies of imidazoliumbased ionic liquids and their solutions [8][9][10][11][12][13][14][15]. Here, we report the first studies of 1 H NMR chemical shifts of trihexyl (tetradecyl) phosphonium chloride ( Fig.…”

The Solid, Liquid and Solution Structural Organization of Imidazolium Ionic Liquids

“…41 Moreover, H,H-NOESY experiments indicate the existence of spin diffusion in 1,3-dialkyimidazolium ionic liquids. 42 Recoil Spectrometry experiments with liquid BMI.PF 6 indicated that bulk stoichiometry is conserved at the surfaces (the surface is neither enriched with the cation nor with the anion). The N-imidazolium atoms and alkyl side chains are deeper in the surface and the average orientation of the cation is with the plane of the ring in the vertical position.…”