Conformationally Adaptive Crown Ether Embedded in a Metal Sulfide for Exceptional Strontium Capture

Precise conformational control of flexible supramolecular moieties (e.g., crown ethers) in crystalline-state adsorbents is essential for efficient host-guest recognition. Traditional strategies relying on covalent chemistry are often limited by either tedious synthesis or a sacrifice of conformational flexibility. Here, we introduce a simple non-covalent anchoring strategy where 18-crown-6 (18Cr6) molecules are in-situ embedded between the interlayer galleries of a perforated thiostannate framework (18Cr6-SnS) in one-pot synthesis. This architecture not only ensures ordered alignment of crown ethers but also preserves the intrinsic coordination freedom, thereby enabling exceptional Sr²⁺ binding affinity. 18Cr6-SnS exhibits a record-high distribution coefficient (K_d = 4.9 × 10⁶ mL/g) under neutral conditions and excellent selectivity in simulated acidic high-level liquid waste, displaying high separation factors (K_d ^Sr/K_d ^M) for Cs⁺ (96), Eu³⁺ (245), and Ni²⁺ (621) in 1 M HNO₃. Experimental and theoretical analyses reveal that the superior Sr²⁺ recognition arises from the conformational adaptability of intercalated crown ethers, coupled with adjustable interlayer spacing. This work establishes a cost-effective and scalable route to develop advanced adsorbents by synergizing host materials with flexible supramolecular receptors for critical energy and environmental applications.