Polyoxometalate-Directed Assembly of Robust Coordination Cages: Overcoming Kinetic Inertness and Conformational...

The selective construction of kinetically robust coordination cages by self-assembly remains a significant challenge in supramolecular chemistry. Herein, we report an efficient polyoxometalate (POM)-directed self-assembly strategy enabling the selective assembly of robust Pt₆L₄ cages under thermodynamic or kinetic control, which is inaccessible via untemplated methods. For a planar ligand (L1) with a dihedral angle (θ = 0°), the POM template promotes the formation of a thermodynamically favored Pt₆(L1)₄ analog. Remarkably, for a twisted and flexible ligand (L2) with a nonideal dihedral angle (θ ≈ 36°), which typically favors the thermodynamically preferred M₁₂L₈ cages, the POM template induces the formation of the kinetically trapped M₆L₄ cages even when using inert Pt(II) precursors. In the absence of POMs, such structures cannot form due to conformational mismatch and the kinetic inertness of metal-ligand coordination. The resulting Pt(II)-based cages are highly stable and remain intact as discrete, template-free hosts after POM removal, capable of encapsulating diverse guests in both acidic and basic aqueous media. This work highlights the unique templating role of POMs in accessing both thermodynamic and kinetic architectures, offering new opportunities for designing robust cages for drug delivery, sensing, and catalysis under harsh conditions.