利用廣泛的拉曼光譜研究1-(4-氰基芐基）-3 -甲基咪唑為基底的離子液體與其熔化過程

Abstract

氰基作為官能的離子液體(ILs) 因呈現較好的溶劑及熱力性質而備受矚目。本論文研究的方式主要是以拉曼光譜學研究以氰基作為官能基離子液體的結構 。由實驗室架設的拉曼顯微光譜儀可以得到很廣泛的震動光譜的資訊，可以從 ~3000 cm−1 (CH 震動區)到 500–2200 cm−1 (CN 震動和陽離子分子內震動)，最後到 ~10–200 cm−1 (分子間和晶格震動)，如此廣泛的光譜範圍有利於我們做震動分析 我們合成五種離子液體，我們以[cbmim]X作為表示。Cbmim為陽離子，1 -（4-氰基芐基）-3 -甲基咪唑的縮寫，而陰離子X為Br−，NTf2−，N(CN)2−，BF4− 和 PF6−。從拉曼光譜10–1000 cm−1 的範圍，根據顯示的光譜圖，我們可以將五種離子液體歸為三類: [cbmim]PF6 和 [cbmim]BF4 都有類似的光譜曲線且擁有較高的沸點(>100 °C)。另外一組，[cbmim]N(CN)2 和 [cbmim]Br，一樣的，在這區域有類似的光譜曲線。相較於這兩組，剩餘的[cbmim]NTf2，由於擁有的陰離子較其餘兩組大，而導致拉曼光譜也與兩者不同。詳細的分析CN 震動波段(約在2230 cm−1)和CH震動波段可以提供離子液體結構上的定性分析。由於[cbmim]N(CN)2 因未能得到較高品質的單晶而未有晶體結構的資訊，所以震動光譜的資訊就相對地能提供一些結構資訊。我們也發現了 再加熱的過程中，[cbmim]Br和 [cbmim]N(CN)2 的CN震動波段有較小的藍位移且從低頻區與CH震動區指出有較強的氫鍵生成而導致有較低的沸點，相反地，在高沸點組的離子液體出現相反的現象。

Nitrile-functionalized ionic liquids (ILs) are an interesting family of ILs that show better solvent and thermal properties. In this work, Raman spectroscopy was used to understand the structural aspects of nitrile-functionalized ILs. The laboratory-built Raman microspectrometer used in the present study covers a broad range of vibrational spectra from ~3000 cm−1 (CH stretch), to 500–2200 cm−1 (CN stretch and mainly cation modes), to ~10–200 cm−1 (intermolecular and lattice vibrations), facilitating comprehensive vibrational analysis. We studied five newly synthesized ILs, [cbmim]X, where the cation is 1-(4-cyanobenzyl)-3-methylimidazolium (abbreviated as cbmim) and the anion X is Br−, NTf2−, N(CN)2−, BF4−, and PF6−. According to the Raman spectral profile in the 10–1000 cm−1 range, the five ILs can be classified into three groups. [cbmim]PF6 and [cbmim]BF4 show a very similar profile and they both have a melting point higher than 100 °C. Another group, [cbmim]N(CN)2 and [cbmim]Br, also shows quite a similar spectral pattern. In contrast, the Raman spectrum of [cbmim]NTf2, which has the bulkiest anion among the five ILs studied, substantially differs from those of the other two groups. Detailed analysis of the CN stretch band at around 2230 cm−1 and the CH stretch bands provides qualitative structural information on the ILs. Such information is in particular useful for [cbmim]N(CN)2, for which X-ray crystallographic data are yet to be obtained owing to the technical difficulty in growing single crystals of large size and high quality. We also find that [cbmim]Br and [cbmim]N(CN)2 show a small blue shift of the CN stretch band during melting and that stronger hydrogen bond formation revealed by the low-frequency and CH stretch Raman spectra results in low melting points of those compounds. An opposite trend is found in the other groups having high melting points.