Studies on the translational and rotational motions of ionic liquids composed of N -methyl- N -propyl-pyrrolidinium (P_(13)) cation and bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide anions and their binary systems including lithium salts

摘要

Room-temperature ionic liquids (RTIL, IL) are stable liquids composed of anions and cations. N -methyl- N -propyl-pyrrolidinium (P13, Py13, PYR13, or mppy) is an important cation and produces stable ILs with various anions. In this study two amide-type anions, bis(trifluoromethanesulfonyl)amide [N (SO _2 CF_3)_2, TFSA, TFSI, NTf_2, or Tf_2 N] and bis(fluorosulfonyl)amide [N (SO_2 F) _2, FSA, or FSI], were investigated. In addition to P13 -TFSA and P13 -FSA, lithium salt doped samples were prepared (P13 -TFSA-Li and P13 -FSA-Li). The individual ion diffusion coefficients (D) and spin-lattice relaxation times (T_1) were measured by H1, F 19, and L7 i NMR. At the same time, the ionic conductivity (σ), viscosity, and density (ρ) were measured over a wide temperature range. The van der Waals volumes of P13, TFSA, FSA, Li (TFSA)_2, and Li (FSA)_3 were estimated by molecular orbital calculations. The experimental values obtained in this study were analyzed by the classical Stokes-Einstein, Nernst-Einstein (NE), and Stokes-Einstein-Debye equations and Walden plots were also made for the neat and binary ILs to clarify physical and mobile properties of individual ions. From the temperature-dependent velocity correlation coefficients for neat P13 -TFSA and P13 -FSA, the NE parameter 1- was evaluated. The ionicity (electrochemical molar conductivity divided by the NE conductivity from NMR) and the 1- had exactly the same values. The rotational and translational motions of P13 and jump of a lithium ion are also discussed.