Fig. 3. Schematic comparison of selected strategies for achieving rationally assembled heteroleptic structures: (a) specific stabilizing interactions between two different ligands; (b) the same, but mediated by a templating guest; (c) geometric design based on shape-complementarity between the different ligands; (d) specific combination of donors around the metal centres guiding the heteroleptic assembly. Approaches (a–c) depend on the shape and functionality of the overall assembly, i.e. the ligand backbones. Strategy (d) is controlled by the immediate environment of the coordinated metal centres. In (a) and (b) the cavity is usually sacrificed but (c) and (d) allow for post-assembly guest uptake.