How Hydrogen Bonds Influence the Mobility of Imidazolium-Based Ionic Liquids. A Combined Theoretical and Experimental Study of 1-n-Butyl-3-methylimidazolium Bromide
How Hydrogen Bonds Influence the Mobility of Imidazolium-Based Ionic Liquids. A Combined Theoretical and Experimental Study of 1-n-Butyl-3-methylimidazolium Bromide
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DOI：
10.1021/jp206974h
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发表时间：
2011-12-29
影响因子：
3.3
通讯作者：
Kirchner, Barbara
中科院分区：
文献类型：
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作者：
Kohagen, Miriam;Brehm, Martin;Kirchner, Barbara
虚拟实验室允许进行真实实验无法进行的计算机实验。在这项工作中，利用先前获得的三个电荷组来研究分子动力学模拟中氢键对咪唑基离子液体的影响。一组提供与实验一致的扩散系数，因此是现实系统的良好模型。与其他组的比较表明氢键对结构和动力学的影响不同。此外，在一种情况下总电荷增加，而在另一种情况下减少了 0.1 e。最酸的质子以及相应的碳原子都被人为地依次且同时设置为零。在最终设置中，质子上带有负电荷，以便为阴离子通过这个酸性最强的氢原子接触阳离子提供屏障。进行了以下观察：改变氢键能力强烈影响结构，而动态特性（例如扩散和粘度）仅发生微弱变化。然而，引入更大的改变（更强的氢键和反氢键）也会强烈影响扩散系数。氢键、离子对和离子笼的动力学都受到氢键水平的影响。总电荷的变化主要影响传输特性而不是结构。对于离子笼动力学的输运特性，我们发现离子对或氢键动力学分别具有良好的相关性和弱相关性或无相关性。然而，氢键确实影响离子笼动力学。因此，我们确认离子液体由松散相互作用的反离子组成，而不是由离散的离子对组成。氢键仅以次要或间接的方式影响性能。
The virtual laboratory allows for computer experiments that are not accessible via real experiments. In this work, three previously obtained charge sets were employed to study the influence of hydrogen bonding on imidazolium-based ionic liquids in molecular dynamics simulations. One set provides diffusion coefficients in agreement with the experiment and is therefore a good model for real-world systems. Comparison with the other sets indicates hydrogen bonding to influence structure and dynamics differently. Furthermore, in one case the total charge was increased and in another decreased by 0.1 e. Both the most acidic proton as well as the corresponding carbon atom were artificially set to zero, sequentially and simultaneously. In the final setup a negative charge was placed on the proton in order to introduce a barrier for the anion to contact the cation via this most acidic hydrogen atom. The following observations were made: changing the hydrogen bonding ability strongly influences the structure while the dynamic properties, such as diffusion and viscosity, are only weakly changed. However, the introduction of larger alterations (stronger hydrogen bonding and antihydrogen bonding) also strongly influences the diffusion coefficients. The dynamics of the hydrogen bond, ion pairing, and the ion cage are all affected by the level of hydrogen bonding. A change in total charges predominantly influences transport properties rather than structure. For ion cage dynamics with respect to transport porperties, we find a good correlation and a weak or no correlation for the ion pair or the hydrogen bond dynamics, respectively. Nevertheless, the hydrogen bond does influence ion cage dynamics. Therefore, we confirm that ionic liquids rather consist of loosely interacting counterions than of discrete ion pairs. Hydrogen bonding affects the properties only in a secondary or indirect manner.