Cation and anion dynamics in supercooled and glassy states of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate: Results from13C,31P, and

Abstract

The rotational dynamics of cations and anions in the room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C 4 mim]PF 6 ) have been investigated in the supercooled liquid and glassy states using 13

A Comparative Study of the Rotational Dynamics of PF6– Anions in the Crystals and Liquid States of 1-Butyl-3-methylimidazolium Hexafluorophosphate: Results from 31P NMR Spectroscopy

“…The α phase and the liquid are comparable in their behavior and are Figure 5). It was shown in a previous study 29 that the τ c of PF 6 − rotation in the supercooled [C 4 mim]PF 6 liquid increases only slightly with decreasing temperature to several tens of picoseconds even below its glass transition (192 K), indicating that this dynamics is not related to the viscous slowdown and is strongly decoupled from the structural relaxation process. The slowest τ c of PF 6 − rotation in the γ phase is consistent with the fact that this phase has the strongest cation−anion interaction and the slowest rotational motions of the cation 31 among all three crystal polymorphs (vide inf ra).…”

“…For example, the values of α, β, and γ phases and the liquid state are estimated to be 31.1 ± 3.0, 10.5 ± 5.9, 153.0 ± 27.2, and 31.3 ± 7.0 ps, respectively, at 200 K. Although, to the best of our knowledge, this is the first report of τ c and E a for PF 6 − rotation in the crystal polymorphs of [C 4 mim]PF 6 , for the liquid, our results are in good agreement with those reported in previous experimental and computational studies. 29,57,58 The ΔM 2 values of 1.0 and 1.6 G 2 are obtained from the simulation of the high temperature T 1 minimum (Figure 4) for the β phase and the liquid, respectively. These ΔM 2 values are comparable with the contributions to the 31 P M 2 from interionic 31 P− 1 H dipolar coupling (see Table 1), suggesting that the high temperature component of 31 P T 1 in Figure 3 is associated with segemental motion of the cation that modulates the 31 P− 1 H dipolar interactions.…”

“…It should be noted that the assignments of the dynamical processes of the constituent ions to 31 P T 1 in [C 4 mim]PF 6 in this work are different from those reported in our previous work. 29 In our previous work on the [C 4 mim]PF 6 liquid, it was assumed that the motional process associated with the 31 P T 1 below 170 K was PF 6 − librational motion and that associated with the high temperature T 1 minimum was the PF 6 − isotropic rotation. These assignments were tentative, as 31 P T 1 data for the liquid were not available above 290 K. In light of the new data presented in this study over a wide range of temperatures, it seems appropriate to explain that the T 1 component observed at lower temperature orignates from isotropic rotation of the anion and that at higher temperature comes from rotational motions of the functional groups of the cation.…”

“…However, to the best of our knowledge, experimental studies on the PF 6 − rotational dynamics in RTILs are practically nonexistent in the liquid or the solid state except in a recent preliminary report by us. 29 Investigation of the PF 6 − dynamics in RTILs is important to understand not only the nature of a specific RTIL but also how RTILs are unique (or not) compared to ordinary salts. Additionally, since some RTILs containing PF 6 − anion crystallize near room temperature, it is possible to compare its rotational dynamics between the liquid and solid states, which is quite difficult for ordinary salts due to their tendency for decomposition before melting.…”

A review of NMR methods used in the study of the structure and dynamics of ionic liquids

“…However, the downfield shift of C2 position is because of the rearrangement of charge distribution among the carbon atoms of the imidazolium ring due to the cation–anion interactions . Endo et al . reported the temperature dependent NMR spectra of [BMIM][PF 6 ] as represented in the Fig.…”