Detecting and quantifying doubly hydrogen bonded anionic dimers in ionic liquids

包括二羧酸根阴离子和二羧酸的二羧酸根物质主要与生物、大气和工业过程相关。用于接收、托管、络合或传感强烈依赖于非共价键合，这是超分子化学的范例。本项目主要是合成和表征离子液体，包括三烷基铵阳离子和单去质子化二元羧酸阴离子。这个想法是在液相中设计氢键结构图案，通过吸引或排斥库仑相互作用加强或削弱。关键的主题包括有趣的双氢键的两个阴离子的羧基之间的环状排列，其中短程定向氢键克服了远程排斥库仑力，通过改变每个阴离子内的羧基和羧酸根之间的距离监测。我们有电荷辅助的+NH...O−和电荷相反的−OH···O−单或双氢键，控制这些模型离子液体的聚集和动力学性质。将通过远红外（FIR）和太赫兹（THz）光谱研究非共价力和氢键排列，这些光谱允许直接解决不同强度的分子间氢键的振动特征。为了了解氢键对动力学的影响，我们测量了阳离子和阴离子的氘核磁共振弛豫时间。我们比较测得的光谱特性，如IR频率，NMR化学位移和四极耦合常数与计算的性能从量子化学计算的复合物和聚集体显示出类似的结构图案和键合。光谱描述符将通过自然键轨道（NBO）的方法进行分析，揭示这些属性之间的相关性。最后但最终的目标是从中性物质中剥离抗衡离子，用于从这些离子液体中分离纯阴离子二聚体，提供通过低温离子振动（CIV）光谱法在气相中检测到的第一种化学稳定的带相同电荷的离子的二聚体。

Dicarboxylate species including both dicarboxylate anions and dicarboxylic acids are mostly relevant in biological, atmospheric and industrial processes. The use for reception, hosting, complexation or sensing strongly depends on non-covalent bonding, which is a paradigm of supramolecular chemistry. In this project, we want to synthesize and characterise ionic liquids, including trialkyl ammonium cations and singly deprotonated dicarboxylic acid anions. The idea is to design hydrogen bonded structural motifs in the liquid phase, strengthened or weakened by attractive or repulsive Coulomb interactions. The key motif includes the intriguing double hydrogen bonded cyclic arrangement between the carboxyl groups of two anions, wherein short-range directional hydrogen bonding overcomes the long-range repulsive Coulomb forces, monitored by varying the distance between the carboxyl and carboxylate groups within each anion. We have charge-assisted +NH…O− and charge-opposed −OH···O− single or double hydrogen bonds that control aggregation and dynamical properties of these model ionic liquids. The non-covalent forces and hydrogen bonding arrangements will be studied by far infrared (FIR) and terahertz (THz) spectroscopy that allow addressing the vibrational signatures of the intermolecular hydrogen bonds of varying strength directly. For understanding the influence of hydrogen bonding on the dynamics, we measure the deuteron NMR relaxation times of cations and anions. We compare the measured spectroscopic properties such as IR frequencies, NMR chemical shifts and quadrupole coupling constants with calculated properties from quantum chemical calculations of complexes and aggregates showing similar structural motifs and bonding. The spectroscopic descriptors will be analysed by means of the natural bond orbital (NBO) approach, revealing the correlation between these properties. A final but ultimate goal is stripping the counter ions from the neutral species for isolating the pure anionic dimers from these ionic liquids, providing the first thermodynamically stable dimers of like-charged ions detected in the gas phase by means of cryogenic ion vibrational (CIV) spectroscopy.