Conformational isomerism and phase transitions in tetraethylammonium bis(trifluoromethanesulfonyl)imide Et4NTFSI
Conformational isomerism and phase transitions in tetraethylammonium bis(trifluoromethanesulfonyl)imide Et4NTFSI
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DOI：
10.1016/j.molstruc.2005.08.028
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发表时间：
2006-02-06
影响因子：
3.8
通讯作者：
Lassègues, JC
中科院分区：
文献类型：
--
作者：
Herstedt, M;Henderson, WA;Lassègues, JC
在熔点为377 K之前，用DSC在277和322 K时检测了四乙基二（三氟甲烷磺酰）亚胺盐（Et4NTFSI）的固相转变。在这个温度范围内，Et4NTFSI固液相的实验拉曼光谱可以用计算的全反式（D-2d）或反式间扭式（S-4）构象的阳离子和反式（C-2）或顺式（C-I）构象的阴离子的频率和强度得到满意的再现。低温有序相III的拉曼光谱表明，阳离子和阴离子分别采用D-2d和C-2构象，通过DFT计算预测其能量低于相应的S-4和C-1构象。在277 K附近的一阶相变以上，大约70%的阳离子转变为S4构象，而C2阴离子的数量逐渐减少（II相）。另一种无序相似乎发生在322和377k之间，此时正离子和阴离子达到两种可能构象的相当数量。在这一相中，阳离子D-2d比S-4稳定4.4 +/- 0.3 U mol(-1)，阴离子C-2比C-1稳定7 + 1 kJ mol（-1）。在液相中，阳离子保持相当数量的D-2d和S-4构象，而大约70%的阴离子采用C-1构象。最后，通过淬火液体或无序相，容易得到过冷的固体相II'。它由C-2阴离子和类似80/20 S-4/D-2d阳离子的混合物组成，大致对应于第二阶段种群的外推。(c) 2005 Elsevier B.V.版权所有
Solid phase transitions are detected by DSC at 277 and 322 K in the tetraethylammonium bis(trifluoromethanesulfonyl)imide salt (Et4NTFSI) before the melting point at 377 K. Over this temperature range, the experimental Raman spectra of the solid and liquid phases of Et4NTFSI can satisfactorily be reproduced using the calculated frequencies and intensities of the cation in its all-trans (D-2d) or trans-gauche (S-4) conformation, and of the anion in its transoid (C-2) or cisoid (C-I) conformation. The Raman spectra of the low-temperature ordered phase III show that the cation and anion adopt the D-2d and C-2 conformations, respectively, predicted by DFT calculations to be of lower energy than the corresponding S-4 and C-1 ones. Above the first order phase transition near 277 K, similar to 70% of the cations are transformed into the S4 conformation while the population Of C2 anions decreases progressively (phase II). Another disordered phase seems to occur between 322 and 377 K where the cations and anions reach comparable populations of their two possible conformations. In this phase I, the cation D-2d form is found to be more stable than the S-4 form by 4.4 +/- 0.3 U mol(-1) and the anion C-2 form is more stable than the C-1 form by 7 + 1 kJ mol(-1). In the liquid phase, the cation keeps comparable populations of the D-2d and S-4 conformers, whereas similar to 70% of the anions adopt the C-1 conformation. Finally, by quenching the liquid or the disordered phases, a supercooled solid phase II' is easily obtained. It is composed of C-2 anions and a mixture of similar to 80/20 S-4/D-2d cations that corresponds roughly to the extrapolation of the phase II populations. (c) 2005 Elsevier B.V. All rights reserved.