Xenon Dynamics in Ionic Liquids: A Combined NMR and MD Simulation Study

Abstract

The translational dynamics of xenon gas dissolved in room-temperature ionic liquids (RTILs) is revealed by 129 Xe NMR and molecular dynamics (MD) simulations. The dynamic behavior of xenon gas loaded in 1-alkyl-3-methylimidazolium chloride, [C n C 1 im]Cl ( n = 6, 8, 10), and hexafluorophosphate, [C n C 1 im][PF 6 ] ( n = 4, 6, 8, 10) has been determined by measuring the 129 Xe diffusion coefficients and NMR relaxation times. The analysis of the experimental NMR data demonstrates that, in these representative classes of ionic liquids, xenon motion is influenced by the length of the cation alkyl chain and anion type. 129 Xe spin–lattice relaxation times are well described with a monoexponential function, indicating that xenon gas in ILs effectively experiences a single average environment. These experimental results can be rationalized based on the analysis of classical MD trajectories. The mechanism described here can be particularly useful in understanding the separation and adsorption properties of RTILs.

129Xe NMR on Porous Materials: Basic Principles and Recent Applications

“…[ 144,145 ] The group also assessed the diffusion of xenon in different IL in order to better understand separation processes in IL phases. [ 146 ] Heinze et al also used 129 Xe NMR along with nitrogen physisorption to evaluate the behavior of IL in porous silica supports such as SBA‐15 and MCM‐41. Particular emphasis was placed on studying the formation of isolated droplets versus layers.…”

Xenon Diffusion in Ionic Liquids with Blurred Nanodomain Separation

“…Therefore, the possibility or xenon to explore both kind of environments, in TFSI salts, makes it more sensitive the overall dynamics of the hosting matrix, and the trend in the diffusion coefficient is indeed in agreement with the increasing viscosity as the chain length is increased. In contrast, when the environment explored by xenon as limited to the alkyl domain, as in [C n C 1 im][Cl], xenon diffusion is not only independent of the increasing viscosity of the matrix but it shows an opposite behaviour thanks to the increasing size and interconnection of the non-polar domains, as was discussed in Ref [53]. Finally, it is interesting to compare the observed trends for all the experimental NMR parameters: diffusion, relaxation and chemical shift.…”

“…work [53] we compared the interaction energy between a xenon atom and the imidazolium alkyl chain, and we found that the FF was in excellent agreement, concerning contact distance and well depth, with the dispersion corrected M06-2X level. Initial boxes were prepared with packmol [74] and contained 400 ion pairs and one xenon atom.…”

“…Initial boxes were prepared with packmol [74] and contained 400 ion pairs and one xenon atom. Xenon parameters were the same as used in Ref.. [53] H-bonds were constrained by the LINCS algorithm. [75] The leap-frog integrator was used with a time step of 1 fs and a cut-off of 10 Å for the van der Waals and short-range electrostatic interaction.…”

The Intermolecular NOE Depends on Isotope Selection: Short Range vs Long Range Behavior

“…Since the interpretation of such spectral features is often nontrivial and may lead to contradicting viewpoints, it can be augmented by molecular dynamics (MD) simulations which serve as a mathematical microscope into the atomistic world. 4 − 6 …”