13C NMR relaxation and reorientation dynamics in imidazolium-based ionic liquids: revising interpretation
The temperature dependencies of 13C 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 13C 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 13C 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 13C NMR relaxation technique allowed its application to ionic liquids to be equally successful as for other liquid systems.