Conformational Adaptivity and Isomerization Pathway Enable Multi-Stimuli-Responsive Assembly and Interconversion of Water-Soluble Metal–Organic Cages

Multi-stimuli-responsive assembly of water-soluble, high-nuclearity metal–organic cages (MOCs) offers attractive opportunities for adaptive supramolecular systems, but balancing structural definition with flexibility remains a central challenge. Here, we report that an adaptive ligand (L2) enables access to a series of M_3nL_2n cages within a single coordination framework, including octahedral, tubular, and bowl-shaped Pd₆(L2)₄ cages, as well as a Pd₁₂(L2)₈ icosahedron. These architectures reversibly interconvert in response to changes in temperature, concentration, solvent environment, and guest binding. In contrast, a rigid analogue (L1) yields a single Pd₆(L1)₄ octahedral cage. Mechanistic studies, combined with single-crystal X-ray diffraction analysis, reveal that interconversion between cages of different nuclearities proceeds primarily via cage isomerization within intact frameworks rather than through classical stepwise growth, providing a kinetically efficient route to higher-order structural complexity and organization. These results establish the integration of conformational adaptivity with cage isomerization pathways as a general design principle for multi-stimuli-responsive supramolecular systems in water.

A conformationally adaptive ligand enables access to multiple water-soluble metal–organic cages (MOCs), including octahedral, tubular, and bowl-shaped M₆L₄ cages and an M₁₂L₈ icosahedron, that reversibly interconvert under external stimuli. Cage isomerization within intact frameworks, rather than classical stepwise growth, governs nuclearity changes, establishing a general design principle for multi-stimuli-responsive supramolecular systems in water.