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.