Cyclodextrin-Directed Assembly of Dynamic Polyoxometalate Pseudo-Rotaxanes

Cyclodextrins (CDs) are widely used as host molecules in supramolecular chemistry, yet their capacity to actively direct structural reorganization of inorganic clusters remains largely unexplored. Here, we demonstrate that α-CD can direct inorganic cluster reorganization during self-assembly, enabling the synthesis of previously inaccessible azobenzene-functionalized polyoxometalate (POM) pseudo-rotaxanes, in which the macrocycle not only encapsulates the organic axle but also governs the structural evolution of the inorganic core. Upon complexation with α-CD, a flat arsonate-functionalized {Mo₆} cluster reorganizes into a bent analogue, yielding a dynamic pseudo-rotaxane assembly (1a@α-CD). Fine pH modulation subsequently induces a CD-mediated transformation into an inverted-Keggin {Mo₁₂} pseudo-rotaxane threaded by four α-CD units. NMR/ITC titration, DOSY/NOESY analyses, and single-crystal x-ray diffraction collectively reveal dual threading pathways and delineate the dynamic {Mo₆} to {Mo₁₂} reorganization process. Crucially, α-CD suppresses precipitation of hydrophobic ligands under strongly acidic conditions and stabilizes transient coordination states, thereby enabling cluster growth pathways inaccessible under identical synthetic conditions in the absence of α-CD. These findings demonstrate that CDs can actively direct inorganic self-assembly through host-guest interactions, providing a supramolecular route to previously inaccessible POM pseudo-rotaxanes and opening new opportunities for adaptive hybrid architectures.