Solvation of Lithium Ion in N,N-Diethyl-N-methyl-N-(2-methoxyethyl)ammonium Bis(trifluoromethanesulfonyl)amide Using Raman and Multinuclear NMR Spectroscopy

The solvation structure of the Li(I) species in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)amide (DEMETFSA) was studied by measuring the Raman and multinuclear NMR spectra of DEMETFSA Solutions containing LiTFSA of various concentrations (0.12 - 1.92 mol kg(-1), [TFSA(-)]/[Li(I)] = 20.0-2.22). It was found from Raman spectra that an intense band clue to the free TFSA(-) anion at around 741 cm(-1) becomes weak, and a new band appears at around 747 cm(-1) with an increase in the concentrations of LiTFSA, and that the pseudoisosbestic point is observed at around 744 cm(-1) in the range of [TFSA(-)]/[Li(I)] = 20.0 - 5.00. From analyses of these Raman bands, the number of TFSA(-) anions bound to the Li+ ion was evaluated to be 1.85 +/- 0.08, and hence, the Li(I) in DEMETFSA Solutions was proposed to exist as [Li(TFSA)(2)](-) in the range of [TFSA(-)]/[Li(I)] = 20.0 - 5.00. Furthermore, in the range of [TFSA(-)]/[Li(I)] = 2.86 - 2.22, the hand observed at around 747 cm(-1) became more strong, and the pseudoisosbestic point disappeared. From these phenomena, it seems that the Li(I) oligomer species are formed in the higher concentration region of LiTFSA. The F-19 NMR signal of the TFSA- anion observed at 42.31 ppm in neat DEMETFSA was found to shift to a higher field linearly with an increase in the concentrations of LiTFSA ([LiTFSA] = 0.00 - 0.99 mol kg(-1), [TFSA(-)]/[Li+] = 20.0 - 3.33), while in a higher concentration range ([LiTFSA] >= 1.26 mol kg(-1), [TFSA(-)]/[Li+] <= 2.86), a slight deviation from linearity was observed. On the other hand, the Li-7 NMR signal did not show ail appreciable shift with increasing LiTFSA concentrations. These results Support that the Li(I) species in DEMETFSA solutions exist as [Li(TFSA)(2)](-) and the Li(I) oligomer species in the low and high concentration regions of LiTFSA, respectively.