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 M3nL2n 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.