Rauber Daniel, Philippi Frederik, Schroeder Daniel, Morgenstern Bernd, White Andrew J P, Jochum Marlon, Welton Tom, Kay Christopher W M
Department of Chemistry, Saarland University Campus B 2.2 66123 Saarbrücken Germany
Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus London W12 0BZ UK
Chem Sci. 2023 Sep 8;14(37):10340-10346. doi: 10.1039/d3sc03240j. eCollection 2023 Sep 27.
Room temperature ionic liquids typically contain asymmetric organic cations. The asymmetry is thought to enhance disorder, thereby providing an entropic counter-balance to the strong, enthalpic, ionic interactions, and leading, therefore, to lower melting points. Unfortunately, the synthesis and purification of such asymmetric cations is typically more demanding. Here we introduce novel room temperature ionic liquids in which both cation and anion are formally symmetric. The chemical basis for this unprecedented behaviour is the incorporation of ether-containing side chains - which increase the configurational entropy - in the cation. Molecular dynamics simulations indicate that the ether-containing side chains transiently sample curled configurations. Our results contradict the long-standing paradigm that at least one asymmetric ion is required for ionic liquids to be molten at room temperature, and hence open up new and simpler design pathways for these remarkable materials.
室温离子液体通常含有不对称有机阳离子。人们认为这种不对称性会增强无序性，从而为强烈的焓驱动离子相互作用提供熵补偿，进而导致熔点降低。不幸的是，此类不对称阳离子的合成和纯化通常要求更高。在此，我们引入了新型室温离子液体，其阳离子和阴离子在形式上都是对称的。这种前所未有的行为的化学基础是阳离子中含有增加构象熵的含醚侧链。分子动力学模拟表明含醚侧链会短暂呈现卷曲构型。我们的结果与长期以来的范式相矛盾，即离子液体要在室温下呈熔融态需要至少一个不对称离子，因此为这些非凡材料开辟了新的、更简单的设计途径。
