Peculiarities of NMR Relaxation in Ionic Liquids: Difficulties in Interpretation and Novel Possibilities

摘要

An applicability of ~(13)C and ~1H relaxation rates (1 /T_1) to direct calculations of the characteristic reorientation time (τ_c) in imidazolium-based ionic liquids has been analyzed. It has shown that ~(13)C NMR relaxation technique can be applied to ionic liquids as successfully as it took place for other liquid systems and allows one to get τ_c values for each carbon directly. The corresponding ~1H data are affected by dipole-dipole interaction only at "higher temperature" range while at lower temperatures spin-diffusion process controls the proton relaxation. Both carbon and hydrogen 1/T_1 dependences are suitable for calculation of τ_c and reveal equal numerical values for a number of functional groups of [emim]Ac at the proper temperature range. On the other hand, ~1H relaxation curves of some functional groups allow one to detect motions, unobservable in the carbon relaxation and, thereby, to extract more information concerning details of the dynamics of the [amim]~+ cations.