Investigation of Fundamental Transport Properties and Thermodynamics in Diglyme-Salt Solutions

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• 作者：Matt Petrowsky ; Roger Frech ; Sophia N. Suarez ; J. R. P. Jayakody ; Steven Greenbaum
• 刊名：Journal of Physical Chemistry B
• 出版年：2006
• 出版时间：November 23, 2006
• 年：2006
• 卷：110
• 期：46
• 页码：23012 - 23021
• 全文大小：127K
• 年卷期：v.110,no.46(November 23, 2006)
• ISSN：1520-5207

文摘

Ionic mobility, the thermodynamics of ionic association, and the structure of associated species are studiedin solutions of diglyme containing either lithium triflate or tetrabutylammonium triflate. Infrared spectroscopic,PFG NMR, thermodynamic, and crystallographic data suggest that the solute species existing in diglyme-lithium triflate are "free" ions, contact ion pairs, and dimers. Equilibrium constants, S, H, and G arecalculated for processes occurring between these species. In particular, the equilibrium constant, correctedfor nonideality using a modified Debye-Hückel expression, is calculated for the dissociation of contact ionpairs into "free" cations and anions. A second equilibrium constant for the formation of dimers from contaction pairs is also calculated; these constants do not significantly vary with salt concentration up to about1.3 × 10^-3 mol cm^-3. The measured temperature dependence of equilibrium constants was used to calculateH and S for the two processes. The value of S = -102 J mol^-1 K^-1 for the dissociation of contaction pairs shows that the large entropy decrease due to cation solvation outweighs the entropy increase due todissociation of a contact ion pair. Ionic mobilities are calculated in lithium triflate-diglyme solutions usingconductivity data in conjunction with information about the nature and concentrations of solute species obtainedfrom IR spectroscopy. Mobilities in tetrabutlyammonium triflate-diglyme solutions are calculated directlyfrom conductivity data. It was concluded that the concentration dependence of the molar conductivity is duein large part to the variation of the ion mobilities with concentration.