Metallo-Supramolecular Self-Assembly with Reduced-Symmetry Ligands

Metallo-supramolecular self-assembly tends to be performed with single metal ions and single, highly symmetrical, ligands. This simplifies the self-assembly process as without sufficient bias within the system a mixture of products may be formed. However, with various applications of metallo-supramolecular species having been demonstrated, the ability to generate more intricate architectures is keenly sought after. The use of reduced symmetry ligands is one route to this goal, and allows access to lower-symmetry assemblies. Multiple coordination pockets can also be introduced in this manner, giving rise to assemblies with metal ions in different coordination environments, which can be exploited for the controlled synthesis of mixed-metal species. Herein we discuss the different approaches that have been used to control self-assembly with low symmetry ligands, including the use of mixed-denticity ligands, the incorporation of geometric constraints, charge separation strategies and the use of repulsive or attractive non-covalent interactions between ligands.