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

Abstract

Ionic mobility, the thermodynamics of ionic association, and the structure of associated species are studied in 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(o), deltaH(o), and deltaG(o) are calculated for processes occurring between these species. In particular, the equilibrium constant, corrected for nonideality using a modified Debye-Hückel expression, is calculated for the dissociation of contact ion pairs into "free" cations and anions. A second equilibrium constant for the formation of dimers from contact ion pairs is also calculated; these constants do not significantly vary with salt concentration up to about 1.3 x 10(-3) mol cm(-3). The measured temperature dependence of equilibrium constants was used to calculate deltaH(o) and deltaS(o) for the two processes. The value of deltaS(o) = -102 J mol(-1) K(-1) for the dissociation of contact ion pairs shows that the large entropy decrease due to cation solvation outweighs the entropy increase due to dissociation of a contact ion pair. Ionic mobilities are calculated in lithium triflate-diglyme solutions using conductivity data in conjunction with information about the nature and concentrations of solute species obtained from IR spectroscopy. Mobilities in tetrabutlyammonium triflate-diglyme solutions are calculated directly from conductivity data. It was concluded that the concentration dependence of the molar conductivity is due in large part to the variation of the ion mobilities with concentration.

Determination of individual contributions to the ionic conduction in liquid electrolytes: Case study of LiTf/PEGDME-150

“…This is directly reflected by the c salt -dependence of the K's (Table 1) as well as by the fact the estimated K values from Bjerrum theory are very different. A further confirmation comes from the results in the case of diglyme [33]. Very similar concentrations for c + , c − , c pair are found there, yet extremely different γ values are derived as a consequence of the very different dielectric constants.…”

“…1e [32,33]. As we found a linearity between total area comprising of these three peaks and c salt , we followed the procedure given in [33] in order to derive concentrations of specific species.…”

“…1e [32,33]. As we found a linearity between total area comprising of these three peaks and c salt , we followed the procedure given in [33] in order to derive concentrations of specific species. Resulting from the analysis, in this concentration, range salt addition hardly changes the concentration of the predominant ion pair species (blue dotted line, Fig.…”

Electron Spin Resonance Studies of the Reorientational Motion of Ni(mnt)2−

“…However, the interactions between Ni(mnt) 2 − and ( n -Bu) 4 N + are expected to be relatively weak because of the steric hindrance of the positively charged nitrogen atom by the bulky n -butyl groups. This is supported by infrared studies of ( n -Bu) 4 NCF 3 SO 3 in diglyme 39 and triglyme, 40 which showed that only free ( n -Bu) 4 N + and CF 3 SO 3 − were present. This was not the case for LiCF 3 SO 3 in diglyme 39 and triglyme 40 as well as NaCF 3 SO 3 in tetraglyme; 41 mixtures of free ions, ion pairs, triple ions, and aggregates were found.…”

Molecular Motion of the Bis(maleonitriledithiolato)nickel Trianion in Solution

“…Solutions of LiCF 3 SO 3 in the same two solvents, however, contained free ions, contact ion pairs, and aggregates. 35,36 …”