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首页> 外文期刊>Chemistry: A European journal >Characterising the electronic structure of ionic liquids: An examination of the 1-butyl-3-methylimidazolium chloride ion pair
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Characterising the electronic structure of ionic liquids: An examination of the 1-butyl-3-methylimidazolium chloride ion pair

机译：表征离子液体的电子结构：检验1-丁基-3-甲基咪唑鎓氯化物离子对

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摘要

In this paper we analyse the electronic properties of gas-phase 1-butyl-3-methylimidazolium Cl ion pairs, [C(4)C(1)iM]Cl, in order to deepen our understanding of ionic liquids in general. Examination of charge densities, natural bond orbitals (NBO), and delocalised molecular orbitals computed at the B3LYP and MP2/6-31++G-(d,p) levels have enabled us to explain a number of experimental phenomena: the relative acidity of different sites on the imidazolium ring, variations in hydrogen-bond donor and acceptor abilities, the apparent contradiction of the hydrogen-bond-donor parameters for different types of solute, the low probability of finding a Cl- anion at the rear of the imidazolium ring and the expansion of the imidazolium ring in the presence of a strong hydrogen-bond acceptor. The unreactive but coordinating environment and large electrochemical window have also been accounted for, as has the strong electron-donating character of the carbon atoms to the rear of the ring in associated imidazolylidenes. The electronic structure of the [C(4)C(1)im](+) cation is best described by a C-4=C-5 double bond at the rear, and a delocalised three-centre 4e(-) component across the front (N-1-C-2-N-3) of the imidazolium ring; delocalisation between these regions is also significant. Hydrogen-bond formation is driven by Coulombic stabilisation, which compensates for an associated destabilisation of the electronic part of the system. Interactions are dominated by a large positive charge at C-2 and the build up of pi-electron density above and below the ring, particularly that associated with the double bond between C-4 and C-5. The NBO partial charges have been computed and compared with those used in a number of classical simulations.
机译：在本文中，我们分析了气相的1-丁基-3-甲基咪唑鎓Cl离子对[C（4）C（1）iM] Cl的电子性质，以加深我们对一般离子液体的理解。在B3LYP和MP2 / 6-31 ++ G-（d，p）水平上计算的电荷密度，天然键轨道（NBO）和离域分子轨道的检查使我们能够解释许多实验现象：相对酸度咪唑环上不同部位的位置，氢键供体和受体能力的变化，不同类型溶质的氢键供体参数的明显矛盾，在咪唑后部发现Cl-的可能性低环和咪唑环在强氢键受体存在下的膨胀。还考虑到无反应但配位的环境和大的电化学窗口，在相关的咪唑基亚烷基中，在环的后部碳原子具有很强的供电子特性。 [C（4）C（1）im]（+）阳离子的电子结构最好由背面的C-4 = C-5双键和横跨整个区域的三中心4e（-）组件描述。咪唑环的前部（N-1-C-2-N-3）;这些区域之间的非本地化也很重要。氢键的形成是由库仑稳定作用驱动的，这可以补偿系统电子部分的相关不稳定作用。相互作用主要由C-2处的大正电荷以及在环的上方和下方（尤其是与C-4和C-5之间的双键相关的pi电子密度）的建立所决定。已计算了NBO的部分费用，并将其与许多经典模拟中使用的费用进行了比较。

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