In this approach, the symmetry of the cage is defined by the geometric relationship between the metal and ligand, as presented by the coordinate vector, from the strong binding affinity and coordination mode of chelating ligands, along with the inherent symmetry of the coordination sites available on the naked metal centre acting as driving force for the assembly process. For example, in a M4L6 tetrahedron, the three coordinate vectors of each metal complex form a chelate plane containing a C3 axis and an angle of 70.6° is required between the coordinate vectors within each ligand to bridge the metal centres (Figure ).