离子液体[BMIM]Br与[BMIM][BF4]配比浓度对Br-离子电荷转移的调节

利用X射线吸收精细结构光谱(XAFS)及紫外吸收光谱两种方法, 分析了离子液体1-丁基-3-甲基咪唑溴盐(BMIM]Br)中逐渐掺入1-丁基-3-甲基咪唑四氟硼酸盐(BMIM]BF₄])时, Br^-阴离子与咪唑阳离子之间氢键作用及电荷偏移量的改变. 随着BMIM]BF₄]加入量增多, Br 元素XAFS近边(XANES)显示吸收峰降低, 吸收边位置向低能端位移0.9 eV; 扩展边(EXAFS)算出径向结构显示Br 与近邻原子间平均配位数降低、平均键长增长; 紫外光谱也有明显蓝移减色效应. 这些结果都表明Br₄^-的掺入改变了Br^-与阳离子间的电荷偏移量, 负电荷更多地转移到Br^-上, 量化计算的数据同样支持该结论.

Effect of the Ratio between Ionic Liquids [BMIM]Br and [BMIM][BF4] on the Charge Transfer of Br-

We analyzed the change of hydrogen bonding between Br^- and imidazolium cations when the ionic liquid 1-butyl-3-methylimidazolium bromide (BMIM]Br) was gradually mixed with 1-butyl-3- methylimidazolium tetrafluoroborate (BMIM] BF₄]) using X-ray absorption fine structure (XAFS) and ultraviolet absorption spectroscopies. As the content of BMIM]BF₄] increased, the intensity of the K-edge main peak of Br reduced in X-ray absorption near edge structure (XANES) spectra, and the absorption edge moved 0.9 eV to lower energy. Meanwhile, the radial structure given by extended X-ray absorption fine structure (EXAFS) indicated that the distribution number reduced and average hydrogen bond length increased. UV spectra showed a clear blue shift and peaks decreased in intensity as the content of BMIM]BF₄] increased. All of these results indicate that more negative charge was transferred to Br^- as the content of BMIM]BF₄] increased. The data obtained from quantum chemical calculations also support this conclusion.