Ionic liquids containing the urea moiety for recognition of halides and complex anions

A series of novel imidazolium based ionic liquids containing the urea moiety were designed and synthesized for anion recognition. 1-Ethylurea-3-methylimidazolium acetate （[Eumim]OAc） was used as the receptor for the halides and complex anions （BF4^-, PF6^-, BPh4^-）.^ 1H NMR spectra showed that the urea protons and imidazolium C（2） proton of the receptor （[Eumim]OAc） moved upfield on addition of various anions. A Job plot showed that the [Eumim]OAc receptor formed a 1 ： 1 complex with BPh4^-. X-ray diffrac- tion analysis and the molecular modeling study revealed that the conformations of [Eumim]OAc and [Eumim]BPh4 were different. The conformational change of the cation was caused by anion exchange, and may provide an alternative to current methods for recognition of anions.