Oligo(ethylene Oxide)–Polyoxometalate Macrocycles

Host–guest chemistry has predominantly advanced within organic systems, whereas the integration of inorganic frameworks into such architectures remains limited. Here, we report two types of organic–inorganic hybrid macrocycles synthesized by cyclizing lacunary Wells–Dawson–type polyoxotungstates with oligo(ethylene oxide) chains. The resulting macrocycles exhibit distinct cavity structures depending on the chain length and show significantly enhanced hydrolytic stability in aqueous solution. The more stable host enables size-selective ion-exchange of the encapsulated K+ ion with alkylammonium cations, whose exchanged forms were crystallographically characterized. Thermodynamic analyses revealed enthalpy–entropy compensation across the guest species, indicating a common binding mechanism governed by desolvation and host conformational changes. This strategy demonstrates a versatile approach for constructing robust hybrid hosts that combine the flexibility of organic macrocycles with the rigidity of inorganic clusters.