Liu Yanhui, Chen Xianze, Men Shuang, Licence Peter, Xi Feng, Ren Zhen, Zhu Weiwei
School of Material Science and Engineering, Shenyang Ligong University, Shenyang, 110159, P. R. China.
School of Chemistry, The University of Nottingham, Nottingham, UKNG7 2RD.
Phys Chem Chem Phys. 2019 Jun 7;21(21):11058-11065. doi: 10.1039/c9cp01381d. Epub 2019 May 15.
In this study, eight 1-alkyl-2,3-dimethylimidazolium ionic liquids are analysed by X-ray photoelectron spectroscopy. The effect of both the anion and the cation on the electronic environment of cationic nitrogen regions is explored. It concludes that the cationic N 1s binding energy shifts to the lower value when the basicity of the anion increases or the acidity of the cation decreases. The impact of the cation acidity on the cation-anion interactions is demonstrated systematically by carefully comparing the binding energies of anion-based components for each anion. It is found that for more basic anions, the charge-transfer effect between counterions can be effectively shielded; for less basic anions, such an effect is negligible. The charge shielding effect of the alkyl substituent is also studied by using dodecyl-based ionic liquids, compared to 1-alkyl-3-methylimidazolium analogues. It suggests that long alkyl substituents can have a significant electron donating effect to the cation headgroup and thus effectively shield the charge-transfer effect between cations and anions.
在本研究中，采用X射线光电子能谱对8种1-烷基-2,3-二甲基咪唑鎓离子液体进行了分析。探讨了阴离子和阳离子对阳离子氮区域电子环境的影响。研究得出，当阴离子的碱性增加或阳离子的酸度降低时，阳离子N 1s结合能向较低值移动。通过仔细比较每种阴离子的基于阴离子的组分的结合能，系统地证明了阳离子酸度对阳离子-阴离子相互作用的影响。研究发现，对于碱性更强的阴离子，抗衡离子之间的电荷转移效应可以得到有效屏蔽；对于碱性较弱的阴离子，这种效应可以忽略不计。与1-烷基-3-甲基咪唑鎓类似物相比，还使用基于十二烷基的离子液体研究了烷基取代基的电荷屏蔽效应。结果表明，长烷基取代基可以对阳离子头基产生显著的供电子效应，从而有效屏蔽阳离子和阴离子之间的电荷转移效应。
