Pyrazolium- versus Imidazolium-Based Ionic Liquids: Structure, Dynamics and Physicochemical Properties

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• 作者：Cinzia Chiappe ; Angelo Sanzone ; Daniele Mendola ; Franca Castiglione ; Antonino Famulari ; Guido Raos ; Andrea Mele
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：January 17, 2013
• 年：2013
• 卷：117
• 期：2
• 页码：668-676
• 全文大小：455K
• 年卷期：v.117,no.2(January 17, 2013)
• ISSN：1520-5207

文摘

Ionic liquids (ILs) composed of two different pyrazolium cations with dicyanamide and bis(trifluoromethanesulfonyl)imide anions have been synthesized and characterized by NMR, Kamlet鈥揟aft solvatochromic parameters, conductivity and rheological measurements, as well as ab initio calculations. Density functional calculations for the two pyrazolium cations, 1-butyl-2-methylpyrazolium [bmpz] and 1-butyl-2,3,5-trimethylpyrazolium [bm₃pz], provide a full picture of their conformational states. Homo- and heteronuclear NOE show aggregation motives sensitive to steric hindrance and the anions鈥?nature. Self-diffusion coefficients D for the anion and the cation have been measured by pulsed field gradient spin鈥揺cho NMR (PGSE-NMR). The ionic diffusivity is influenced by their chemical structure and steric hindrance, giving the order D_cation > D_anion for all of the examined compounds. The measured ion diffusion coefficients, viscosities, and ionic conductivity follow the Vogel鈥揊ulcher鈥揟ammann (VFT) equation for the temperature dependencies, and the best-fit parameters have been determined. Solvatochromic parameters indicate an increased ion association upon going from bis(trifluoromethanesulfonyl)imide to dicyanamide-based pyrazolium salts, as well as specific hydrogen bond donor capability of H atoms on the pyrazolium ring. All of these physical properties are compared to those of an analogous series of imidazolium-based ILs.