A series of N,N′-dialkylimidazolium room temperature ionic liquids (RTILs) with nonafluorobutanesulfonate ([C_nmim][NFBS], n = 5–8) were synthesized and characterized by elemental analysis, NMR, SCXRD, and DSC. Although any [C_nmim][NFBS] studied here were sticky “ionic liquids” right after the preparation, they have crystallized after standing at room temperature for several hours or days. Mechanical stimuli like agitation with a spatula onto the crystalline [C_nmim][NFBS] (n = 5–7) resulted in unexpected melting of these salts, whereas such a behavior was not observed for [C₈mim][NFBS]. The DSC analyses clarified that [C_nmim][NFBS] (n = 5–7) exhibit multiple phase transitions from 268 to 303 K including several pre-melting stages probably due to molecular motions of the alkyl or perfluoroalkyl chains. Furthermore, pressure dependency of the melting point revealed that any of the RTILs studied here exhibit negative dP/dT slopes. Such a characteristic thermal behavior observed here is ascribed to the C–H···O and C–H···F hydrogen bond networks to form hydrophilic and hydrophobic domains in the crystal lattices and also to give loosely packed crystal structures.

中文翻译：

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N，N'-二烷基咪唑鎓九氟丁烷磺酸盐离子液体的结构化学和刺激响应相变

合成了一系列带有九氟丁烷磺酸盐（[C _n mim] [NFBS]，n = 5-8）的N，N'-二烷基咪唑鎓室温离子液体（RTIL），并通过元素分析，NMR，SCXRD和DSC进行了表征。尽管此处研究的任何[C _n mim] [NFBS]都是刚制备后的粘性“离子液体”，但它们在室温下放置数小时或数天后已结晶。机械刺激（例如用刮刀在晶体[C _n mim] [NFBS]上搅动（n = 5-7）导致这些盐意外熔化，而对于[C ₈ mim] [NFBS]未观察到这种行为。DSC分析明确指出，[C_n mim] [NFBS]（ n = 5-7）表现出从268 K到303 K的多个相变，包括几个预熔融阶段，这可能是由于烷基或全氟烷基链的分子运动所致。此外，熔点的压力依赖性表明，此处研究的任何RTIL都具有负d P / d T斜率。此处观察到的这种特征性热行为归因于C–H···O和C–H···F氢键网络，它们在晶格中形成亲水和疏水域，并产生疏松堆积的晶体结构。