Like-charge attraction in Ionic Liquids: The influence of pressure, polarity and molecular mimics

在第一个资助期，我们表明，阴离子的相互作用强度，阳离子的极化率，和阳离子的羟基烷基基团的长度控制氢键阳离子-阴离子和阳离子-阳离子簇之间的微妙平衡在散装离子液体。我们研究了同电荷离子团簇的动力学和热力学稳定性。与耶鲁大学的约翰逊小组合作，我们开始了最初的气相实验，显示阳离子复合物与阳离子之间的合作氢键，尽管它们之间有很强的排斥力。实验结果也为关于所谓“反静电氢键”稳定性的讨论提供了线索。大量令人兴奋的结果之间的吸引力的相互作用的离子一样的电荷引发进一步的问题，我们要解决的更新建议：如何敏感的阳离子簇形成压力？我们是否可以通过使用不同极性的溶剂来改变介电介质，从而控制阳-阴离子对和阳-阳离子团簇之间的微妙平衡？与溶剂分子的特定相互作用有多重要？我们能通过用分子模拟物取代阳离子来增强氢键和簇的形成吗？在这里，从离子到分子团簇的顺利转移进行了研究。与约翰逊小组合作，我们还计划调查是否阳离子和分子气相簇的结构图案也存在于散装液相。我们将通过精心选择的离子液体的合成、本体和气相红外光谱以及量子化学方法的适当组合来应对这些挑战。

In the first funding period, we showed that the interaction strength of the anion, the polarizability of the cation, and the length of hydroxy alkyl groups of the cation control the delicate balance between hydrogen-bonded cation-anion and cation-cation clusters in bulk ionic liquids. We investigated the kinetic and thermodynamic stabilities of clusters of like-charged ions. In collaboration with the Johnson group at Yale University, we started initial gas phase experiments, showing cationic complexes with cooperative hydrogen bonding between the cations despite the strong repulsive forces between them. The experimental results also shed light onto the discussion about the stability of so-called “Anti electrostatic hydrogen bonds”. The plethora of exciting results about the attractive interaction between ions of like charge provokes further questions, which we want to address in the renewal proposal: How sensitive is the cationic cluster formation to pressure? Can we control the delicate balance between cation-anion ion-pairs and the cation-cation clusters by changing the dielectric medium using solvents of different polarity? How important are specific interactions with solvent molecules? Can we enhance hydrogen bonding and cluster formation by replacing the cations by their molecular mimics? Here, the smooth transfer from ionic to molecular clusters is studied. In collaboration with the Johnson group, we also plan to investigate whether the structural motifs of cationic and molecular gas phase clusters are also present in the bulk liquid phase. We will tackle these challenges with a suitable combination of synthesis of well-selected ionic liquids, bulk and gas phase infrared spectroscopy, and quantum chemical methods.