The encapsulation of small molecules by molecular “capsules” is an important field within supramolecular chemistry due to its relevance to biochemistry, waste treatment, catalysis and medicine. Much work has focused on the binding of neutral and cationic species with great success, however few hosts capable of anion encapsulation are known. Transition-metal modification of Cryptophanes A, E and O with [Cp*Ru-][CF₃SO₃] at each arene face has resulted in cationic capsules with π-acidic cavities that demonstrate a remarkable ability to selectively encapsulate anions. Importantly, binding of anions exterior to the cavity “turns off” binding at its interior in a predictable fashion. More recently, a novel synthetic route has resulted in water soluble [Cp*Ru-][Cl] metalated cryptophanes. The binding of neutral and anionic species in water by these hosts is being explored.