Character and influence of hydrogen bonding on the microstructures of ionic liquids by means of neutron diffraction and molecular dynamics simulations

在本项目中，我们希望通过中子衍射（ND）和分子动力学（MD）模拟研究羟基功能化离子液体（IL）中氢键的双面性。在最近的实验研究中，我们已经表明，在这个IL家族中，两种不同类型的氢键（HB）共存：阳离子和阴离子之间的传统HB（ca）和两个阳离子之间的难以捉摸的HB（cc），由于带相同电荷的离子之间的库仑排斥力，应该要弱得多。尽管有这种预期，但是，我们观察到的结构图案涉及氢键阳离子簇在散装液体和气相。在对纯羟基官能化离子液体的初步ND实验中，我们测量了两种类型氢键的距离，表明尽管阳离子之间存在排斥作用，但（cc）HB比（ca）HB短10 ppm。羟基官能化离子液体中氢键的双面性质允许解决我们在这里解决的基本问题。首先，将OH-官能化的离子液体与非官能化的离子液体混合提供了关于OH-缺陷对离子液体中（ca）和（cc）簇的尺寸和分布的影响的信息。其次，将IL与模拟IL阳离子的醇分子混合，允许通过从离子改变为ML来研究电荷缺陷时的液体纳米结构。第三，添加强极性质子受体分子竞争IL中的OH-基团打开了通过OH-捕捉剂控制HB分布的路径。改变羟基和电荷缺陷上的氢键簇的大小和分布或引入OH-捕集剂，允许调节离子液体及其混合物的性质，这两者都吸引了越来越多的科学和技术的兴趣。直接测定（H... O）和（O... O）键距，表明羟基官能化的离子和分子液体中的HB强度，只能通过ND实验和MD模拟的支持。

In this project, we want to study the double-faced nature of hydrogen bonding in hydroxyl-functionalized ionic liquids (ILs) by means of neutron diffraction (ND) and molecular dynamics (MD) simulations. In recent experimental studies, we have shown that in this IL family, two distinct types of hydrogen bonds (HBs) coexist: The conventional HBs between cation and anion (ca) and elusive HBs between two cations (cc) that are supposed to be much weaker due to the repulsive Coulomb force between the like-charged ions. Despite this expectation, however, we observed structural motifs involving hydrogen-bonded cationic clusters in the bulk liquid and the gas phase. In preliminary ND experiments on pure hydroxyl-functionalized ILs, we have measured the distances for both type hydrogen bonds, showing that the (cc) HBs are 10 ppm shorter than the (ca) HBs despite the repulsive interaction between the cations. The double-faced nature of hydrogen bonding in hydroxyl-functionalized ILs allows tackling fundamental questions, which we address here. Firstly, mixing OH-functionalized with non-functionalized ILs provides information about the influence of OH-defects on the size and distribution of (ca) and (cc) clusters in ILs. Secondly, mixing the IL with alcohol molecules mimicking the IL cation, allows studying the liquid nanostructures upon charge-defects by changing from the ionic to the ML. Thirdly, adding a strong polar proton acceptor molecule competing for the OH-groups in the IL opens a path for controlling the HB distribution by an OH-catcher. Varying the size and distribution of hydrogen bonded clusters upon hydroxyl- and charge-defects or introducing OH-catchers, allows tuning the properties of ILs and their mixtures, which are both attracting increasing interest in science and technology. The direct determination (H…O) and (O…O) bond distances, indicating the HB strengths in hydroxyl-functionalized ionic and molecular liquids, is only accessible through ND experiments and support of MD simulations.