Cooperative Silver Ion-Pair Recognition by Peralkylated Pillar[5]arenes

Ion-pair recognition of metal salts by pillararenes has never been reported. This limits the further development and applications of pillararene supramolecular chemistry. Herein we report the first examples of pillararene-based metal ion-pair recognition. They are host–guest complexes between three peralkylated pillar[5]­arenes and the silver salt CF₃COOAg. Single crystal X-ray analysis shows that CF₃COOAg forms a unique dinuclear silver structure that penetrates into the pillar[5]­arene cavity in these complexes. Besides the silver-π interactions, multiple C–H···O and C–H···F hydrogen bonds between the counterion and the pillar[5]­arene host also contribute to stabilizing and maintaining the host–guest structures. Moreover, benefiting from the silver ion-pair recognition, perethylated pillar[5]­arene EtP5 can be used as a solid absorbent to capture CF₃COOAg from solution efficiently, showing a potential application in precious metal extraction and recycling.