Nuclear Magnetic Resonance Study of the Dynamics of Imidazolium Ionic Liquids with -CH2Si(CH3)3 vs -CH2C(CH3)3 Substituents

详细信息    查看全文

• 作者：Song H. Chung ; Richard Lopato ; Steven G. Greenbaum ; Hideaki Shirota ; Edward W. Castner Jr. ; James F. Wishart
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：May 10, 2007
• 年：2007
• 卷：111
• 期：18
• 页码：4885 - 4893
• 全文大小：208K
• 年卷期：v.111,no.18(May 10, 2007)
• ISSN：1520-5207

文摘

Trimethylsilylmethyl (TMSiM)-substituted imidazolium bis(trifluoromethylsulfonyl)imide (NTf₂^-), and tetrafluoroborate (BF₄^-) ionic liquids (ILs) have lower room-temperature viscosities by factors of 1.6 and 7.4,respectively, than isostructural neopentylimidazolium ILs. In an attempt to account for the effects of siliconsubstitution in imidazolium RTILs and to investigate the ion dynamics, we report nuclear magnetic resonance(NMR) measurements of ¹H (I = 1/2) and ¹⁹F (I = 1/2) spin-lattice relaxation times (T₁) and self-diffusioncoefficients (D) as a function of temperature for ILs containing the TMSiM group and, for comparison, theanalogous neopentyl group. The ¹H and ¹⁹F nuclei probe the dynamics of the cations and anions, respectively.The low-temperature line shapes were determined to be Gaussian, and the onset of the rigid lattice line widthis correlated with the measured glass transition temperature. The spin-lattice relaxation data feature a broadT₁ minimum as a function of inverse temperature for both nuclear species. The Arrhenius plots of the diffusiondata for both nuclear species are found to exhibit Vogel-Tammann-Fulcher curvature. Analysis of the and D data generally show fractional Stokes-Einstein behavior D (T/)^m. This is most prominent in theneopentylimidazolium BF₄^- IL with m 0.66.