Two distinct allosteric active sites regulate guest binding within a Fe₈Mo₁₂¹⁶⁺ cubic receptor.

The binding of phosphine ligands to molybdenum sites on the faces of a supramolecular cube served to inhibit allosterically the encapsulation of a neutral or anionic guest. The edges of the cube also provided a distinct second allosteric site, where the binding of tetraphenylborate also allosterically inhibited anion binding in the cube's cavity. The two allosteric sites were shown to regulate the binding of an anionic guest either independently or in concert. The use of a tertiary amine as an allosteric effector also enabled a phosphine guest to be ejected from the cube's cavity into solution, to generate phosphine complexes with other metal ions.