Structures of Ionic Liquids with Different Anions Studied by Infrared Vibration Spectroscopy

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• 作者：Yoonnam Jeon ; Jaeho Sung ; Choongwon Seo ; Hyunjin Lim ; Hyeonsik Cheong ; Minhyuck Kang ; Bongjin Moon ; Yukio Ouchi ; Doseok Kim
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：April 17, 2008
• 年：2008
• 卷：112
• 期：15
• 页码：4735 - 4740
• 全文大小：158K
• 年卷期：v.112,no.15(April 17, 2008)
• ISSN：1520-5207

文摘

We investigated the structures of ionic liquids (1-butyl-3-methylimidazolium iodide [BMIM][I] and 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄]) and their aqueous mixtures using attenuated totalreflection (ATR) infrared absorption and Raman spectroscopy. The ATR spectrum in the CH_x (x = 1, 2, 3)vibration region from 2800 to 3200 cm^-1 was very different between [BMIM][BF₄] and [BMIM][I] eventhough all the spectral features in this region were from the butyl chain and the imidazolium ring of the samecation. The spectrum did not change appreciably irrespective of the water concentration for [BMIM][BF₄],whereas the spectrum from [BMIM][I] showed significant changes as the water concentration was increased,especially in CH-vibration modes from the imidazolium ring. For very diluted solutions both aqueous mixturesof [BMIM][I] and [BMIM][BF₄] showed very similar spectra. Mixing of [BMIM][I] with heavy water (D₂O)facilitated the isotopic exchange of the proton attached to the most acidic carbon of the imidazolium ring intodeuterium from D₂O, whereas even prolonged exposure to D₂O did not induce any isotopic exchange for[BMIM][BF₄]. Raman spectra around 600 cm^-1 indicative of the butyl chain conformation also changeddifferently as the water concentration was increased between [BMIM][I] and [BMIM][BF₄]. These differencesare considered to come from the variation in the position of the anion, where I^- is expected to be closer tothe C(2) hydrogen of the imidazolium cation and interacting more specifically as compared to BF₄^-.