Step-by-Step Self-Assembly of a Double-Walled Knotted Cage With Increasing Topological Complexity

The self-assembly process of a double-walled cage formed from a semiflexible tripodal ligand and a Pd(II) 90-degree block was tracked by NMR and x-ray analysis. At least two intermediate structures with distinct topologies were observed prior to the formation of the final double-walled cage. By optimizing the self-assembly conditions (e.g., time, solvent, and concentration), these topological intermediates were successfully isolated and analyzed by x-ray crystallography. They are considered crucial metastable structures that navigate the shortest pathway to the final structure, demonstrating the critical role of molecular topology in guiding and controlling the kinetics of metal-directed self-assembly.