Securing a Supramolecular Architecture By Tying a Stopper Knot

We report on a rotaxane‐like architecture secured by the in situ tying of an overhand knot in the tris(2,6‐pyridyldicarboxamide) region of the axle through complexation with a lanthanide ion (Lu3+). The increase in steric bulk caused by the knotting entanglement locks a crown ether onto the thread. Removal of the lutetium ion unties the knot and, if the axle binding site for the ring is deactivated, the macrocycle spontaneously de‐threads. If the binding interaction is switched on again, the crown ether re‐threads over the 10 nm length of the untangled strand. The overhand knot can be re‐tied, re‐locking the threaded structure, by adding lutetium ions once again.