Nuclear magnetic resonance studies on the rotational and translational motions of ionic liquids composed of 1-ethyl-3-methylimidazolium cation and bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide anions and their binary systems including lithium salts

Room temperature ionic liquids (ILs) are stable liquids composed of anions and cations. 1-ethyl-3-methyl-imidazolium (EMIm, EMI) is a popular and important cation that produces thermally stable ILs with various anions. In this study two amide-type anions, bis(trifluoromethanesulfonyl) amide [N(SO2CF3)(2), TFSA, TFSI, NTf2, or Tf2N] and bis(fluorosulfonyl) amide [(N(SO2F)(2), FSA, or FSI] were investigated by multinuclear NMR spectroscopy. In addition to EMIm-TFSA and EMIm-FSA, lithium-salt-doped binary systems were prepared (EMIm-TFSA-Li and EMIm-FSA-Li). The spin-lattice relaxation times (T-1) were measured by H-1, F-19, and Li-7 NMR spectroscopy and the correlation times of H-1 NMR, tau(c)(EMIm) (8 x 10(-10) to 3 x 10(-11) s) for the librational molecular motion of EMIm and those of Li-7 NMR, tau(c)(Li) (5 x 10(-9) to 2 x 10(-10) s) for a lithium jump were evaluated in the temperature range between 253 and 353 K. We found that the bulk viscosity (eta) versus tau(c)(EMIm) and cation diffusion coefficient D-EMIm versus the rate 1/tau(c)(EMIm) have good relationships. Similarly, linear relations were obtained for the eta versus tau(c)(Li) and the lithium diffusion coefficient D-Li versus the rate 1/tau(c)(Li). The mean one-jump distances of Li were calculated from tau(c)(Li) and D-Li. The experimental values for the diffusion coefficients, ionic conductivity, viscosity, and density in our previous paper were analyzed by the Stokes-Einstein, Nernst-Einstein, and Stokes-Einstein-Debye equations for the neat and binary ILs to clarify the physicochemical properties and mobility of individual ions. The deviations from the classical equations are discussed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3625923]