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.