The 1-ethyl-3-methylimidazolium-tetrafluoroborate (EMI-BF4) room-temperature molten salt was investigated with NMR techniques. Diffusion coefficients measured at temperatures ranging from 300 to 360 K indicate phase-change occurred in the vicinity of 333 K, which is supported by 11B quadrupolar relaxation rates. Combined with the sizes of diffusion particles obtained form the Stokes-Einstein equation, this phase change is ascribed to that the diffusion particle is transformed from "discrete ion-pair" to "individual ion" at temperatures above 335 K due to decomposition of the EMI-BF4 ion pair. Analysis of the 13C dipole-dipole relaxation rates identifies the formation of hydrogen bond(C2H…F) between the counter ions, EMI+ and BF4-. That the values of viscosity in EMI-BF4 are higher than those in EMI-AlCl4 at corresponding temperatures is therefore understood according to the viscosity approach employed to investigate the H-bonding in molten salts.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry
- Atomic and Molecular Physics, and Optics