Keplerates are cages that are similar to edge-transistive {Cu} MOFs with AX stoichiometry. In fact, they can be thought of as metal-organic polyhedra. These cages are quite different than the types previously discussed as they are much larger, and contain many cavities. Complexes with large diameters can be desirable as target guest molecules are becoming more large and complex. These cages have multiple shells, like an onion. Secondary building units such as dinuclear {Cu} acetate species are used as building blocks.
In the cage above, the outer shell is a cuboctohedron; its structure comes from two adjacent benzoate moieties from the m-BTEB ligand. The third benzoate is attached to the inner shell. The {Cu} units in the inner sphere adapt several different orientations. The labile complexes in the inner sphere allow binding of large target guests on the nanometer scale. Building a complex of this size that is still soluble is a challenge.