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.
Highlights
Results and discussionAs a first step we have repeated the measurements of 13C T1 in the same ionic liquid as in ref. 8–10 namely, [bmim]PF6
This appeared to be necessary, as we could not find in ref. 8–10 the primary information, i.e. tables of relaxation times at various temperatures
A chemical structure of the [bmim]+ cation is shown in Scheme 1 together with an attribution of the lines
Summary
Results and discussionAs a first step we have repeated the measurements of 13C T1 in the same ionic liquid as in ref. 8–10 namely, [bmim]PF6. The tc magnitude can be calculated at each temperature using eqn (1) and the obtained value for A0. If one uses the root #1 in the whole temperature range, the calculations lead to a conventional temperature dependence of tc for all spectral lines, it is not necessary to involve additional experimental procedures, such as NOE, in order to transform 1/T1 experimental data into tc magnitudes.
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