Poster

Concentration-Dependent Dynamics in Solvate Ionic Liquids via NMR Relaxometry

L. Kruse, T. Winter, J. K. Philipp-Taube, A. Strate, D. Paschek, R. Ludwig
1. Physical and Theoretical Chemistry, University of Rostock, Albert-Einstein-Str. 27, 18059 Rostock/DE
2. Department Life, Light & Matter, University of Rostock, Albert-Einstein-Str. 25, 18059 Rostock/DE
3. Leibniz Institut für Katalyse an der Universität Rostock e.V., Albert-Einstein-Str. 29a, 18059 Rostock/DE
lennart.kruse@uni-rostock.de

Abstract

In contrast to conventional Ionic Liquids (ILs), which consist of organic and/or inorganic ions, the so-called Solvate Ionic Liquids (SILs) are being formed by mixing a salt and a solvent, which form stochiometric chelate complexes. These room-temperature liquids have been studied extensively regarding their electrolyte properties such as conductivity and self-diffusion.[1] To shed more light on the ion- and molecule specific dynamics, fast field cycling (FFC) NMR relaxometry is used to measure the frequency-dependent T1 spin-lattice relaxation times (Fig. 1). By fitting the relaxation rates (R1 = 1/T1) to relaxation models the self-diffusion coefficients and rotational correlation times of different species are determined. This method has proven to be well suited to investigate neat ILs.[2] However, literature involving FFC studies on SILs systems is scarce. To address this shortcoming, we investigate the SIL consisting of lithium bis(trifluoromethylsulfonyl)imide (LiNTf2) and triethylenglycoldimethylether (triglyme/G3). In this SIL, the triglyme coordinates the Li+ cation in a crown-ether like manner and thereby forms complexes like [Li(G3)1]+, as it has been shown by MD simulations and far-infrared measurements.[3] However, the structure of these complexes highly depends on the concentration of the salt. To address the concentration effect on the dynamics we probed two different lithium salt/triglyme mixtures over a broad temperature range, with salt:solvent ratios of 1:1 and 1:2, yielding structures like [Li(G3)1][NTf2] and [Li(G3)2][NTf2]. By measuring the T1 spin-lattice relaxation times of 1H and 19F nuclei using FFC NMR, we obtain dynamic information of the G3 and NTf2 anions, respectively. Finally, we find good agreement between experimentally obtained values of self-diffusion coefficients and rotational correlation with those derived from MD simulations.

Figure from Kruse1.docx

Figure 1 – Temperature-dependent 1H NMR dispersion profiles of the SIL [Li(G3)2][NTf2] obtained from fast field cycling NMR relaxometry.

References

[1] T. Tamura et al., Chemical Letters, 39, 753 (2010).

[2] L. Kruse et al., Journal of Physical Chemistry Letters, 15, 10410 (2024).

[3] J. K. Philipp et al., ChemPhysChem, 26, e202400991 (2025).