Molecular motions and ion diffusions of the room-temperature ionic liquid 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPImTFSA) studied by 1H, 13C, and 19F NMR.
Molecular motions and ion diffusions of the room-temperature ionic liquid 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPImTFSA) studied by 1H, 13C, and 19F NMR.
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通过 1H、13C 和 19F NMR 研究室温离子液体 1,2-二甲基-3-丙基咪唑鎓双(三氟甲基磺酰基)酰胺 (DMPImTFSA) 的分子运动和离子扩散。
DOI：
10.1021/jp802392t
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
S. Seki
中科院分区：
文献类型：
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作者：
K. Hayamizu;S. Tsuzuki;S. Seki
通过脉冲场梯度自旋回波核磁共振测量离子电导率和离子扩散系数，研究了咪唑类室温离子液体（RTIL） 1,2-二甲基-3-丙基咪唑双（三氟甲基磺酰基）酰胺（DMPImTFSA）的扩散特性。观察到与温度相关的(1)H、（19）F和（13）C核磁共振自旋-晶格弛豫时间T(1)值，DMPIm的(1)H T(1)对各种质子显示最小T(1)值。根据Bloemberger-Purcell-Pound （BPP）方程，直接从(1)H NMR计算相关时间tau(c)值。利用(1)H τ (c)值，对含有质子的碳原子的（13）c - T(1)进行了评价。DMPIm分子运动的tau(c)从253 K时的1.3 ns变化到353 K时的72 ps。Stokes-Einstein-Debye （SED）模型表明，tau(c)太短，无法在室温附近进行整体分子重定向。因此，提出了小角度分子旋转的可能性，并利用平移扩散系数、本研究中测量的体粘度和由(1)ht(1)数据得到的τ (c)在283 ~ 353 K温度范围内计算了暂定翻转角。翻转振幅随温度的升高而增大。DMPIm除了具有亚甲基节段运动、甲基旋转运动和咪唑环的构象交换等快速分子内运动外，还具有具有温度依赖性振幅的各向同性重定向运动。证明了TFSA快速运动的存在性。离子的平移扩散是目前RTIL中最慢的动态过程。通过从头算分子轨道计算了解了DMPIm（+）和TFSA（-）稳定配合物的几何形状，并计算了分离离子的形成能。计算结果对于解释咪唑环质子的(1)H - T(1)行为具有重要意义。
The diffusive properties of an imidazolium room-temperature ionic liquid (RTIL), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPImTFSA), are studied from the ionic conductivity and the ion diffusion coefficients measured by pulsed field gradient spin echo NMR. The temperature-dependent (1)H, (19)F, and (13)C NMR spin-lattice relaxation time T(1) values were observed, and the (1)H T(1) for DMPIm showed T(1) minima for various protons. According to the Bloemberger-Purcell-Pound (BPP) equation, the correlation time tau(c) values were directly calculated from (1)H NMR. By using the (1)H tau(c) values, an evaluation of the (13)C T(1) was attempted for the carbons having protons. The tau(c) estimated for molecular motions of DMPIm changes from 1.3 ns at 253 K to 72 ps at 353 K. The Stokes-Einstein-Debye (SED) model suggests that the tau(c) is too short for the overall molecular reorientation near room temperature. Consequently, the possibility of small-angle molecular rotation is proposed and tentative flip angles are calculated by using the translational diffusion coefficient, the bulk viscosity measured in this study, and the tau(c) obtained from (1)H T(1) data in the temperature range between 283 and 353 K. The flip amplitude increases with the temperature. DMPIm has isotropic reorientational motions with temperature-dependent amplitude, in addition to fast intramolecular motions such as methylene segmental motions, methyl rotational motion, and conformational exchange of the imidazolium ring. The existence of fast motions of TFSA is also shown. The translational diffusion of the ions is the slowest dynamic process in the present RTIL. Ab initio molecular orbital calculations are performed to understand the geometries of stable complexes of DMPIm(+) and TFSA(-), and the formation energies from the isolated ions are evaluated. The computed results are important for interpreting the (1)H T(1) behaviors observed for the imidazolium ring protons.