Hydrogen bonding mediated ion pairs of some aprotic ionic liquids and their structural transition in aqueous solution  

作　　者：Huiyong Wang Miao Liu Yuling Zhao Xiaopeng Xuan Yang Zhao Jianji Wang 

机构地区：[1]Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals,School of Chemistry and Chemical Engineering,Key Laboratory of Green Chemical Media and Reactions,Ministry qf Edueation,Henan Normal University,Xinxiang 453007,China

出　　处：《Science China Chemistry》2017年第7期970-978,共9页中国科学（化学英文版）

基　　金：supported by the National Natural Science Foundation of China(21573060,21673068);Program for Innovative Research Team in Science and Technology in University of Henan Province(16IRTSTHN002);Plan for Scientific Innovation Talent of Henan Province(144200510004);The High Performance Computing Center of Henan Normal University

摘　　要：Ion pair speciation of ionic liquids(ILs) has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential. It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them. Considering the fact that far-IR(FIR) spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding, in this work, this spectroscopic technique has been combined with molecular dynamic(MD) simulation and nuclear magnetic resonance hydrogen spectroscopy(~1H NMR) to investigate ion pairs of aprotic ILs [Bmim][NO_3], [BuPy][NO_3], [Pyr_(14)][NO_3], [PP_(14)][NO_3] and [Bu-choline][NO_3] in aqueous IL mixtures. The FIR spectra have been assigned with the aid of density functional theory(DFT) calculations, and the results are used to understand the effect of cationic nature on the structure of ion pairs. It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion, were still maintained in aqueous solutions up to high water mole fraction(say 0.80 for [BuPy][NO3]). When water content was increased to a critical mole fraction of water(say 0.83 for [BuPy][NO3]), the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water. With the further dilution of the aqueous ILs solution, the solvent-separated ion pairs was finally turned into free cations and free anions(fully hydrated cations or anions). The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions(fully hydrated ion) were dependent on the cationic structures. These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous solution. MD simulation and ~1H NMR results support the conclusion drawn from FIR spectra investigaIon pair speciation of ionic liquids（ILs） has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential. It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them. Considering the fact that far-IR（FIR） spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding, in this work, this spectroscopic technique has been combined with molecular dynamic（MD） simulation and nuclear magnetic resonance hydrogen spectroscopy（~1H NMR） to investigate ion pairs of aprotic ILs [Bmim][NO3], [BuPy][NO3], [Pyr（14）][NO3], [PP（14）][NO3] and [Bu-choline][NO3] in aqueous IL mixtures. The FIR spectra have been assigned with the aid of density functional theory（DFT） calculations, and the results are used to understand the effect of cationic nature on the structure of ion pairs. It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion, were still maintained in aqueous solutions up to high water mole fraction（say 0.80 for [BuPy][NO3]）. When water content was increased to a critical mole fraction of water（say 0.83 for [BuPy][NO3]）, the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water. With the further dilution of the aqueous ILs solution, the solvent-separated ion pairs was finally turned into free cations and free anions（fully hydrated cations or anions）. The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions（fully hydrated ion） were dependent on the cationic structures. These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous solution. MD simulation and ~1H NMR results support the conclu

关 键 词：ionic liquids ion pair hydrogen bonding far infrared spectroscopy solution 

分 类 号：O645.1[理学—物理化学]