Effect of Water on the Local Structure and Phase Behavior of Imidazolium-Based Protic Ionic Liquids
Effect of Water on the Local Structure and Phase Behavior of Imidazolium-Based Protic Ionic Liquids
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DOI：
10.1021/jp510691e
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发表时间：
2015-01-29
影响因子：
3.3
通讯作者：
Martinelli, Anna
中科院分区：
文献类型：
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作者：
Yaghini, Negin;Pitawala, Jagath;Martinelli, Anna
我们报告了水对两种质子离子液体 C(2)HImTFSI 和 C(2)HImTfO 的局部结构和相行为的影响。采用拉曼光谱和红外光谱来研究局部配位状态。我们发现水与 TFSI- 相互作用较弱，更具体地说，通过 -SO3 基团与 TfO- 相互作用。此外，我们观察到，添加水后，C(2)HImTFSI 中的 -NH 伸缩频率没有变化，而 C(2)HImTfO 中的 -NH 伸缩频率发生红移，表明不同的氢键构型。通过在 800-1000 cm(-1) 频率范围内发现环面外弯曲 (?) 模式的一些附加特征的出现，我们假设在 C(2)HImTFSI 中，水仅与与环 C2H 和 N3H 位点配位的阳离子相互作用，而它与 C(2)HImTfO 中的阳离子和阴离子相互作用，形成涉及阳离子 N-H 位点的氢键以及阴离子-SO3基团。这些不同的局部结构也反映在 DSC 研究的相行为中，表明与 H2O/C(2)HImTFSI 混合物相比，当将水添加到 C(2)HImTfO 中时，溶液更加均匀。最后，我们报告水的添加也会显着影响 T-m 和 T-g。
We report on the effect of water on local structure and phase behavior of two protic ionic liquids, C(2)HImTFSI and C(2)HImTfO. Raman and infrared spectroscopy are employed to investigate the local coordination state. We find that water interacts weakly with TFSI- while more specifically with TfO- through the - SO3 group. Additionally, we observe that upon addition of water the - NH stretching frequency does not change in C(2)HImTFSI, while it red-shifts in C(2)HImTfO, indicative of different hydrogen bonding configurations. Supported by the appearance of some additional features in the 800-1000 cm(-1) frequency range where ring out-of-plane bending (?) modes are found, we hypothesize that in C(2)HImTFSI water interacts only with the cation coordinating to the ring C2H and the N3H sites, while it interacts with both cation and anion in C(2)HImTfO forming hydrogen bonds that involve the cationic N-H site as well as the anionic - SO3 group. These different local structures also reflect in the phase behavior investigated by DSC, which reveals a more homogeneous solution when water is added to C(2)HImTfO, as compared to H2O/C(2)HImTFSI mixtures. Finally we report that the addition of water also significantly affects both T-m and T-g.