Conformational adaptability enabled higher-order self-sorting processes in coordination cages

Understanding the key role of conformational adaptability in biological processes is crucial to mimic the remarkable applications inherent to biological systems. Motivated by the efficacy of conformational adaptability, we equipped a conformationally-adaptive ligand in low-symmetry cis-Pd₂L^a ₂L^x ₂-type coordination cages. A family of five cis-Pd₂L^a ₂L^x ₂-type cages was assembled by complementary ligand pairing of a conformationally adaptable converging ligand (L^a-type) in combination with diverging rigid ligands (L^x-type) of different lengths. Integrative self-sorting of the individual cages showed that the converging ligand adapts to three distinct conformations in the Pd₂L^a ₂L^x ₂-type architecture, to accommodate L^x-type ligands of varying sizes. Through a series of experiments, we found a higher order, i.e., 2-fold heteromeric completive self-sorting outcomes of two co-existing Pd₂L^a ₂L^x ₂-type cages, where two chosen complementary rigid ligands could induce any two different conformations of the converging ligand in the co-existing cages. Then we further pushed the intricacy and demonstrated the unprecedented 3-fold heteromeric completive self-sorting in coordination cage systems, where the conformationally-adaptive ligand adapts three distinct conformations in three co-existing Pd₂L^a ₂L^x ₂-type cages. This study paves the way for the utility of conformational adaptability to achieve switchable size, shape, and functionality in supramolecular systems toward bio-relevant applications.