[EPy]Cl和[EPy]Br离子对的气相和液相结构及阴阳离子间的相互作用

Structure and Interaction of Ion-Pairs of [EPy]Cl and [EPy]Br in Gas and Liquid Phases

采用密度泛函理论B3LYP/6-31+G(d,p)方法对氯化乙基吡啶([EPy]Cl)、溴化乙基吡啶([EPy]Br)的离子对进行了结构优化和频率分析,并利用自洽反应场(SCRF)的导体极化连续模型(CPCM)考察了离子液体液相下的结构及相互作用.得到了两种离子液体的离子对在气相、液相下最稳定结构及气相红外光谱特征值,两种离子液体的离子对结构存在相似性,红外光谱特征值与文献值比较吻合.应用自然键轨道(NBO)理论分析了离子对中原子电荷分布及电荷转移情况,结果证明两种离子液体中阴阳离子间除了静电相互作用外还存在着氢键作用.通过对比气相及液相下的几何参数、相互作用能及NBO分析结果,发现液相下阴阳离子的相互作用明显降低.液相环境抵消了大部分阴阳离子间的静电作用,导致液相下阴阳离子间相互作用的减小.

The structures of ionic liquids N-ethyl-pyridinium chloride （[EPy]Cl） and N-ethyl-pyridinium bromide （[EPy]Br） were studied by density functional theory （DFT） and B3LYP/6-31＋G（d,p） calculations. Structures and interactions in liquid phase were investigated by conductor-like polarizable continuum model （CPCM）. The geometries of ionic liquids in gas phase were fully optimized by energy gradient technology and the number of imaginary frequency was obtained through vibrational analysis. The simulated infrared spectra agreed well with the experimental infrared spectra. Natural bond orbital （NBO） analysis was performed to analyze the atomic charges and charge transfers in the monomers and complexes in gas and liquid phases. The interaction between the anion and the cation was mainly electrostatic. There were also some hydrogen bonds between cations and anions in ionic liquids. According to the geometry structures, the magnitude of the interaction energies of [EPy]Cl and [EPy]Br and the NBO analysis results, the interaction between the anion and the cation became more weak in liquid phase because the liquid environment counteracted part of the electrostatic interaction between the anion and the cation.