A Coordination Cage That Shrinks via Single-Site Labilization to Reshape Encapsulated Guests

To achieve on-demand mechanical control over encapsulated guests, a molecular host must be both structurally robust and dynamically responsive, which are notoriously difficult to reconcile in self-assembled systems. Here, we introduce a single-site labilization strategy, where a single labile site is installed into an otherwise kinetically inert coordination cage. We synthesized a heterometallic PdPt8L6 cage with a chemically detachable site by incorporating one labile Pd(II) unit onto a stable Pt8L6 scaffold. This design enables the cage to switch between expanded and contracted states without releasing its guest, thereby mechanically controlling the guest's shape. This mechanical control translates into a hierarchical function: regulating secondary guest binding to the encapsulated host molecule. This approach provides a blueprint for designing advanced molecular machinery with multistate, on-demand functions.