# A Wide-Ranging NMR Probe for Multiscale Structures
## 5 Applications
### Liquids, Mixtures, and Solutions  
The highly polarizable electron cloud of xenon is strongly altered when this species is dissolved in liquid phases. Naturally, this is reflected in its NMR signal, which, analogously to solid materials, can be used to obtain in-depth structural and morphological information along with knowledge about phase separation, dynamics, and presence and size of different domains. Owing to these important features, \({}^{129}\)Xe NMR has been used to study a variety of pure liquids, mixtures, solutions, and host-guest complexes in the liquid phase [51, 52, 53, 54, 55, 56, 57]. Ionic liquids (ILs) can be defined as salts whose melting point is below 100 \({}^{\circ}\)C [58]. In the last two decades, they have attracted much attention thanks to their unique physical properties, such as thermal stability [59], outstanding solvent properties [60], and the possibility to tailor their properties by carefully choosing their constituents [61, 62]. Even though they are often treated as simple solvents, they are complex structured materials whose properties are frequently associated to their organization on the nano and on the micro scales [63]. A thorough structural and morphological characterization of ionic liquids is mandatory to obtain important structures-property relationships, useful both in understanding the characteristics of these materials and in designing task-specific ionic liquids. The structure of a series of 1-alkyl-3-methylimidazolium-based ionic liquids has been studied in 2013 with \({}^{129}\)Xe NMR [19]. Xenon dissolved in ionic liquids gave chemical shifts in the broad range between 150 and 250 ppm (Figure 1), with a very strong dependence on the nature of the anion, a weak temperature dependence in the range 305-340 K, and a negligible xenon pressure dependence. Chemical shift data were correlated to the average size of the cages probed by xenon in the NMR time scale, using the calculated average cage size for xenon in benzene as a reference (5.3 A, chemical shift \(\delta\) = 188.1 ppm). The average cage size increased when going from halide anions to bulky, noncoordinating anions, such as [TfN2]\({}^{-}\). Good agreement was also found between these results and the crystal structure data found in literature. In another recent work, the dynamics of xenon in 1-alkyl-3-methylimidazolium chloride and hexafluorophosphate ionic liquids were studied combining NMR and molecular dynamics [64]. Pulsed gradient spin echo experiments allowed the diffusion coefficients of \({}^{129}\)Xe, \({}^{19}\)F, and \({}^{1}\)H to be measured. The calculated \({}^{129}\)Xe diffusion coefficient was about an order of magnitude smaller than that of \({}^{129}\)Xe in water (2.2 \(\times\) 10\({}^{-9}\) m\({}^{2}\) s\({}^{-1}\)) and in alkanes, and it increased with increasing the alkyl chain length, while the diffusion coefficients of \({}^{19}\)F and \({}^{1}\)H followed an opposite trend. This indicated that the influence of the structural organization of ILs on the dynamics of these species was significantly different. The increase in viscosity with the alkyl chain length caused a decrease in the mobility of the anion-cation components. On the other hand, the extension of the nonpolar components favored xenon diffusion, with a much more significant increase in the Cl\({}^{-}\) ILs. These results pointed to the existence of segregated polar and nonpolar domains, the size and interconnectivity of the latter increasing with the alkyl chain length, creating more free volume easily accessible by xenon and, consequently, enhancing its diffusion. Moreover, it was observed that the nanosegregation was stronger in chloride salts with respect to hexafluorophosphate salts. Interestingly, different results were obtained in a later work where bis(trifluoromenthanesulfonyl)imide (TFSI) was chosen as the anion part: xenon diffusion coefficients slightly decreased with increasing the alkyl chain length [65].