Thermal and Electrochemical Stability of Tetraglyme–Magnesium Bis(trifluoromethanesulfonyl)amide Complex: Electric Field Effect of Divalent Cation on Solvate Stability

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 °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 °C. Above 250 °C, desolvation of the Mg2+ ion takes place and G4 evaporates. On the other hand, the weight loss starts at around 140 °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...