Palumbo O, Trequattrini F, Cimini A, Tsurumaki A, Navarra M A, Paolone A
CNR-ISC, U.O.S. La Sapienza, Piazzale A. Moro 5, 00185 Rome, Italy.
Department of Physics, University of Rome "La Sapienza", Piazzale A. Moro 5, 00185 Rome, Italy.
J Phys Chem B. 2021 Mar 11;125(9):2380-2388. doi: 10.1021/acs.jpcb.0c11429. Epub 2021 Feb 24.
The intra- and intermolecular interactions in ether-functionalized ionic liquids (ILs) are studied by means of infrared (IR) spectroscopy measurements of -ethoxyethyl--methylpiperidiniumbis(fluorosulfonyl)imide (P-FSI) and -ethoxyethyl--methylmorpholiniumbis(fluorosulfonyl)imide (M-FSI). The temperature dependence of the spectra in the medium IR range allows the study of the anion conformer distribution and its variation during phase transitions. In particular, it is found that for both ILs the trans conformer of FSI is more stable than the cis conformer, and the enthalpy differences between them are calculated and are found to decrease upon the addition of a Li salt. The results obtained in the far IR range, combined with ab initio calculation of the ionic couple performed using the B3LYP-D functional and considering both empirical dispersion corrections and the presence of a polar solvent, provide evidence for the occurrence of a hydrogen bonding between the O atom of the anion and its closest H atoms directly linked to a C atom of the cation. The comparison with samples having the same cations but with bis(trifluoromethanesulfonyl)imide (TFSI) as an anion, that is, M-TFSI and P-TFSI, as well as with samples having cations without the ether-functionalization neither in the ring nor in the side chain, such as -propyl--methylpyrrolidinium-FSI (PYR-FSI) and 1-butyl-1-methylpyrrolidinium-TFSI (PYR-TFSI), indicates that the occurrence of such highly directional interaction between anion and cation is better observable in the ether-functionalized samples, in particular in those containing FSI as an anion.
通过对2-乙氧基乙基-1-甲基哌啶双（氟磺酰）亚胺（P-FSI）和2-乙氧基乙基-1-甲基吗啉双（氟磺酰）亚胺（M-FSI）进行红外（IR）光谱测量，研究了醚官能化离子液体（ILs）中的分子内和分子间相互作用。中红外范围内光谱的温度依赖性使得能够研究阴离子构象异构体分布及其在相变过程中的变化。特别地，发现对于这两种离子液体，FSI的反式构象异构体比顺式构象异构体更稳定，并计算了它们之间的焓差，发现加入锂盐后焓差减小。在远红外范围内获得的结果，结合使用B3LYP-D泛函并考虑经验色散校正和极性溶剂的存在对离子对进行的从头算，为阴离子的O原子与其直接与阳离子的C原子相连的最接近H原子之间存在氢键提供了证据。与具有相同阳离子但以双（三氟甲磺酰）亚胺（TFSI）作为阴离子的样品，即M-TFSI和P-TFSI，以及与在环和侧链中均无醚官能化的阳离子的样品，如1-丙基-1-甲基吡咯烷鎓-FSI（PYR-FSI）和1-丁基-1-甲基吡咯烷鎓-TFSI（PYR-TFSI）进行比较，表明在醚官能化样品中，特别是在含有FSI作为阴离子的样品中，阴离子和阳离子之间这种高度定向相互作用的发生更易于观察到。
