Selective Construction of Pseudo-Mortise-and-Tenon-Type Molecules

Ring-in-ring complexes typically suffer from limited stability, as the interactions between the inner and outer macrocycles rely predominantly on nondirectional van der Waals forces or directional hydrogen bonding alone. To address this limitation, we identified a novel stabilization strategy based on the mortise-and-tenon principle from the crystal structure of assembly Rh-1. In this architecture, the three characteristic cavities inherent in the classic ring-in-ring framework are defined as the "mortise", while a one-dimensional molecular chain is rationally designed to act as the complementary "tenon". Through precise insertion of the tenon into the mortise, dense and continuous π-π stacking interactions as well as extensive van der Waals contact surfaces are successfully established within the ring-in-ring skeleton. Such directional and efficient molecular packing significantly strengthens the overall intermolecular forces, thereby substantially increasing the dissociation energy barrier. Furthermore, structurally analogous complex Ir-1 can be readily synthesized using the same assembly protocol. Guided by the pseudo-mortise-and-tenon platform, we further constructed molecular figure-eight knots, Rh-2 and Ir-2, and metalla[2]catenanes, Rh-3 and Ir-3, by judiciously tuning the folding angle and length of the organic bridging ligands.