Endo Takatsugu, Sunada Kouki, Sumida Hiroki, Kimura Yoshifumi
Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University 1-3 Tatara Miyakodani Kyotanabe Kyoto 610-0394 Japan
Department of Applied Chemistry, Graduate School of Science and Engineering, Doshisha University 1-3 Tatara Miyakodani Kyotanabe Kyoto 610-0394 Japan.
Chem Sci. 2022 Jun 8;13(25):7560-7565. doi: 10.1039/d2sc02342c. eCollection 2022 Jun 29.
Ionic liquids (ILs) are salts with an extremely low melting point. Substantial efforts have been made to address their low melting point from the enthalpic standpoint ( interionic interactions). However, this question is still open. In this study, we report our findings that entropic (large fusion entropy), rather than enthalpic, contributions are primarily responsible for lowering the melting point in many cases, based on a large thermodynamic dataset. We have established a computational protocol using molecular dynamics simulations to decompose fusion entropy into kinetic (translational, rotational, and intramolecular vibrational) and structural (conformational and configurational) terms and successfully applied this approach for two representatives of ILs and NaCl. It is revealed that large structural contribution, particularly configurational entropy in the liquid state, plays a deterministic role in the large fusion entropy and consequently the low melting point of the ILs.
离子液体（ILs）是熔点极低的盐类。人们已从焓的角度（离子间相互作用）做出了大量努力来研究其低熔点问题。然而，这个问题仍然没有定论。在本研究中，基于大量的热力学数据集，我们报告了我们的发现：在许多情况下，降低熔点的主要原因是熵（大的熔化熵）贡献而非焓贡献。我们建立了一种使用分子动力学模拟的计算方法，将熔化熵分解为动力学（平动、转动和分子内振动）和结构（构象和构型）项，并成功地将这种方法应用于两种离子液体和氯化钠的代表物。结果表明，大的结构贡献，特别是液态下的构型熵，在离子液体的大熔化熵以及由此导致的低熔点中起着决定性作用。
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