Molecular reorientation in ionic liquids: A comparative dielectric and magnetic relaxation study

We have used 2H magnetic relaxation to study the single-particle reorientation of the 1-ethyl-3-methylimidazolium ([emim]+) ion in two prototypical low-viscosity ionic liquids comprising the bis(trifluoromethylsulfonyl)imide ([Tf2N]−) and dicyanimide ([(CN)2N]−) anions. Hydrodynamic analysis reveals extremely low (‘subslip’) coupling factors not captured by existing theories. Comparison with the microwave dielectric spectrum of [emim][Tf2N] shows that the dominant diffusive component of the dielectric response can be rationalized by single-particle reorientation of the cations.