Control of ligand exchange rate between coordination cages by the steric bulk of the ligand and the coordinating solvent

Understanding the intricacies of self-assembly and ligand exchange has wide-ranging applicability in current inorganic chemistry and in the future design and assembly of complex, functional materials incorporating metal-ligand motifs. Ligand exchange between two paddlewheel-based M4L4 cages results in the formation of a near-statistical mixture of homo- and hetero-leptic species. Steric bulk allows tuning of the lability of the ligands in the coordination cage complexes with bulkier ligands forming cages having half-lives ca. three times that of the least hindered species. Solvent plays an important role in the lability of the ligands of the coordination cages; larger solvent molecules coordinated to the exterior of the metal nodes provide a stabilizing effect, slowing the rate of ligand exchange. In some instance the final equilibrium position is slightly perturbed by the combination of steric bulk from the two ligands, suggesting that the self-assembly process are not trivial.