Selective Recognition of Chloride Anion in Water.

A tricationic cage was synthesized via click chemistry. The cage has a preorganized cavity, which is surrounded by six relatively acidic C-H bonds. In organic solvent, the cage can recognize a variety of anions, among which the Cl anion has the highest binding affinity due to size selectivity. The cage is also able to selectively recognize the Cl anion in water, even though the binding affinity is just moderate.