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- Mandai, Toshihiko, 1984, et al.
(author)
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Pentaglyme-K salt binary mixtures: phase behavior, solvate structures, and physicochemical properties
- 2015
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 17:4, s. 2838-2849
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Journal article (peer-reviewed)abstract
- We prepared a series of binary mixtures composed of certain K salts (KX) and pentaglyme (G5) with different salt concentrations and anionic species ([X](-) : [(CF3SO2)(2)N](-) = [TFSA](-), [CF3SO3](-) = [TfO](-), [C4F9SO3](-) = [NfO](-), PF6-, SCN-), and characterized them with respect to their phase diagrams, solvate structures, and physicochemical properties. Their phase diagrams and thermal stability strongly implied the formation of equimolar complexes. Single-crystal X-ray crystallography was performed on certain equimolar complexes, which revealed that G5 molecules coordinate to K+ cations in a characteristic manner, like 18-crown-6 ether in the crystalline state, irrespective of the paired anions. The solvate structures in the molten state were elucidated by a combination of temperature-dependent Raman spectroscopy and X-ray crystallography. A drastic spectral variation was observed in the [K(G5)(1)][TfO] Raman spectra, indicating that solvate structures in the crystalline state break apart upon melting. The solvate stability of [K(G5)(1)]X is closely related to the ion-ion interaction of the parent salts. A stable solvate forms when the ion-dipole interaction between K+ and G5 overwhelms the ion-ion interaction between K+ and X-. Furthermore, the physicochemical properties of certain equimolar mixtures were evaluated. A Walden plot clearly reflects the ionic nature of the molten equimolar complexes. Judging from the structural characteristics and dissociativity, we classified [K(G5)(1)]X into two groups, good and poor solvate ionic liquids.
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2. |
- Terada, S., et al.
(author)
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Thermal and Electrochemical Stability of Tetraglyme-Magnesium Bis(trifluoromethanesulfonyl)amide Complex: Electric Field Effect of Divalent Cation on Solvate Stability
- 2016
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:3, s. 1353-1365
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Journal article (peer-reviewed)abstract
- Phase behavior of binary mixtures of tetraglyme (G4) and Mg[TFSA]2 (TFSA: bis(trifluoromethanesulfonyl)amide) was investigated. In a 1:1 molar ratio, G4 and Mg[TFSA]2 formed a stable complex with a melting point of 137 degrees C. X-ray crystallography of a single crystal of the complex grown from a G4-Mg[TFSA]2 binary mixture revealed that the G4 molecule wraps around Mg2+ to form a complex [Mg(G4)](2+) cation, and the two [TFSA](-) anions also participate in the Mg2+ coordination in the crystal. The thermal stability of [Mg(G4)][TFSA](2) was examined by thermogravimetry, and it was found that the complex is stable up to 250 degrees C. Above 250 degrees C, desolvation of the Mg2+ ion takes place and G4 evaporates. On the other hand, the weight loss starts at around 140 degrees C in solutions containing excess G4 (n > 1 in Mg[TFSA]2:G4 = 1:n) due to the evaporation of free (uncoordinated) G4. The suppression of G4 volatility in the [Mg(G4)][TFSA]2 complex is attributed to strong electrostatic and induction interactions between divalent Mg2+ and G4. In addition, complexation of G4 with Mg2+ is effective in enhancing the oxidative stability of G4. Linear sweep voltammetry revealed that the oxidative decomposition of [Mg(G4)][TFSA]2 occurs at electrode potentials >5 V vs Li/Li+, while the oxidation of uncoordinated G4 occurs at around 4.0 V. This oxidative stability enhancement occurs because the HOMO energy level of G4 is reduced by complexation with Mg2+, which is supported by the ab initio calculations.
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