¹³C NMR relaxation and reorientation dynamics in imidazolium-based ionic liquids: revising interpretation

Abstract

The temperature dependencies of (13)C NMR relaxation rates in [bmim]PF6 ionic liquid have been measured and the characteristic times (τc) for the cation reorientation have been recalculated. We found the origin of the incorrect τc temperature dependencies that were earlier reported for ring carbons in a number of imidazolium-based ILs. After a correction of the approach (13)C T1, the relaxation data allowed us to obtain the characteristic times for an orientation mobility of each carbon, and a complicated experiment, such as NOE, was not required. Thus the applicability of (13)C NMR relaxation rate measurements to the calculation of the characteristic times for reorientation of all the carbons of the [bmim](+) cation was confirmed and our findings have shown that a (13)C NMR relaxation technique allowed its application to ionic liquids to be equally successful as for other liquid systems.

Ion pair and solvation dynamics of [Bmim][BF4] + water system

“…Analysing equation and considering that the dependence of T 1 with temperature as a function of τ C , 13 C T 1 reaches a minimum when τ C ω C = 0.791. Using the experimental value of T 1 minimum for each carbon, we can obtain the value of the constant A 0 ( ) and therefore determine at each temperature the correlation time as described by Matveev et al. This methodology allows the determination of the correlation time directly from the relaxation data without the need of NOE information; however, this methodology is limited to the carbons that show a minimum T 1 .…”

“…and therefore determine at each temperature the correlation time as described by Matveev et al [46] . This methodology allows the determination of the correlation time directly from the relaxation data without the need of NOE information; however, this methodology is limited to the carbons that show a minimum T 1 .…”

Molecular mobility in several imidazolium‐based ionic liquids according to data of 1H and 13C NMR relaxation

“…It is necessary to note that the temperature dependences of 13 C relaxation rates in [bmim]PF 6 and in some other ILs had been measured earlier by Carper and coauthors in a series of works, [4,[7][8][9][10][11] see also comments. [2,3] For [bmim]BF 4 , 13 C the relaxation curves had been also obtained previously [12,13] and the data of Brui [13] have been further used. Also in the latter work, 13 C relaxation dependences have been measured for [emim]OAc and the first comparison has been made for all three studied ILs, [13] see Figures S1-S4.…”

Reorientation dynamics and ion diffusivity of neat dimethylimidazolium dimethylphosphate probed by NMR spectroscopy

“…These values are consistent with results obtained by others for imidazolium ring carbons and attached methyl groups. 19,23,41,42,64 The tted E A /E VFT values are nearly unaffected by the inclusion of CSA to the analysis of the relaxation data. Only the combination of BPP spectral density function, including the CSA relaxation mechanism and a VFT type s c temperature dependency results in high E VFT values of 17-23 kJ mol À1 and low T 0 values for the [C 1 C 1 IM] + carbons (Table 2C).…”

“…In the fast intramolecular motion limit (s i ( s c ) eqn (8) reduces to J(u) ¼ S 2 J(u) BPP . One elegant way to extract information about molecular mobility from 13 C longitudinal relaxation times under the assumption of fast intramolecular motion and neglecting the CSA contribution is given in great detail in recent publications by Matveev et al [41][42][43] With the knowledge of the precise 13 C T 1 minimum it is possible to independently simplify the determination of the value of S 2 (S 2 ¼ u C /(1.87A 0 T min 1 )) and hence to calculate s c for any given T 1 . Sometimes the relaxation of viscous liquids, even far above the melting point, is insufficiently described by eqn (6) or (8) and a correlation time distribution should be included into J(u).…”