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

在第一个资助期，我们发现阴离子的相互作用强度、阳离子的极化性和阳离子的羟基烷基长度控制着体积离子液体中正阴离子和正阳离子之间的微妙平衡。我们研究了类电荷离子簇的动力学和热力学稳定性。在与耶鲁大学Johnson小组的合作下，我们开始了最初的气相实验，展示了阳离子配合物，尽管它们之间有很强的排斥力，但阳离子之间有协同氢键。实验结果也为所谓的“防静电氢键”的稳定性的讨论提供了线索。关于同类电荷离子之间的吸引相互作用的大量令人兴奋的结果引发了进一步的问题，我们希望在更新提案中解决这些问题：阳离子簇的形成对压力有多敏感？我们是否可以通过使用不同极性的溶剂来改变介电介质来控制阳离子-阴离子对和阳离子-阳离子簇之间的微妙平衡？与溶剂分子的特定相互作用有多重要？我们能否通过用它们的分子模拟物取代阳离子来增强氢键和簇的形成？本文研究了离子簇向分子簇的平滑转移。在与Johnson小组的合作中，我们还计划研究阳离子和分子气相簇的结构基序是否也存在于散装液相中。我们将通过精心选择的离子液体合成，体和气相红外光谱以及量子化学方法的适当组合来解决这些挑战。

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.