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.