Yoshii Kazuki, Uto Takuya, Tachikawa Naoki, Katayama Yasushi
Department of Applied Chemistry, Faculty of Science and Technology, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan and Department of Energy and Environment, Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan.
Organization for Promotion of Tenure Track, University of Miyazaki, Nishi 1-1 Gakuen-Kibanadai, Miyazaki 889-2192, Japan.
Phys Chem Chem Phys. 2020 Sep 16;22(35):19480-19491. doi: 10.1039/d0cp02662j.
Room temperature ionic liquids (RTILs) containing ether oxygen atoms have been investigated for a gamut of science and technology applications owing to their superior physicochemical properties. However, the effect of the position of the ether oxygen atom in the side chain on their physicochemical properties is not clearly understood. This study investigates, using both experimental and computational approaches, the effect of ether oxygen atoms on the physicochemical properties of RTILs consisting of bis(trifluoromethylsulfonyl)amide (TFSA-) with 1-methyl-1-propylpyrrolidinium (MPP+), 1-butyl-1-methylpyrrolidinium (BMP+), 1-methoxymethyl-1-methylpyrrolidinium (MOMMP+), 1-ethoxymethyl-1-methylpyrrolidinium (EOMMP+), and 1-methoxyethyl-1-methylpyrrolidinium (MOEMP+). The viscosity of the RTILs containing the ether oxygen atom was lower than that of the alkyl analogues. Moreover, the viscosity of EOMMPTFSA was lower than that of MOEMPTFSA, albeit EOMMPTFSA and MOEMPTFSA have the same molecular weight with ether oxygen atoms at different positions. Ab initio calculations reveal that the number of methylene groups between nitrogen and oxygen atoms in the cation structure profoundly impacts the local stable structure of the cation. Furthermore, we discussed the relationship between the transport properties and the spatial distribution of ions obtained by MD simulations. This result will be valuable in the design of functionalized RTILs, via the judicious tuning of the conformational flexibility of ether oxygen atoms in related ionic liquids.
由于具有优异的物理化学性质，含醚氧原子的室温离子液体（RTILs）已被广泛研究用于一系列科学技术应用中。然而，侧链中醚氧原子的位置对其物理化学性质的影响尚不清楚。本研究采用实验和计算方法，研究了醚氧原子对由双（三氟甲基磺酰）酰胺（TFSA-）与1-甲基-1-丙基吡咯烷鎓（MPP+）、1-丁基-1-甲基吡咯烷鎓（BMP+）、1-甲氧基甲基-1-甲基吡咯烷鎓（MOMMP+）、1-乙氧基甲基-1-甲基吡咯烷鎓（EOMMP+）和1-甲氧基乙基-1-甲基吡咯烷鎓（MOEMP+）组成的RTILs物理化学性质的影响。含醚氧原子的RTILs的粘度低于烷基类似物。此外，尽管EOMMPTFSA和MOEMPTFSA分子量相同且醚氧原子位于不同位置，但EOMMPTFSA的粘度低于MOEMPTFSA。从头算计算表明，阳离子结构中氮和氧原子之间的亚甲基数量对阳离子的局部稳定结构有深远影响。此外，我们还讨论了通过分子动力学模拟获得的离子传输性质与空间分布之间的关系。通过合理调节相关离子液体中醚氧原子的构象灵活性，这一结果将对功能化RTILs的设计具有重要价值。
