<p>Due to the analogous physicochemical properties and weak coordination ability of alkali and alkaline earth metals, accurate separation of radioactive ⁹⁰Sr from groundwater or seawater still presents a big challenge in environmental radioactivity remediation. Here we mimic the complexation behavior of molecular crown-ether carboxylic acids to construct an elegant negatively charged supramolecular trap in an anionic crown ether-based metal-organic framework (ZJU-X99) for precisely catching Sr²⁺. Owing to the synergistic effects of electrostatic interactions arising from the In(COO)₄^- nodes and supramolecular host-guest recognition from the 18-crown-6 rings, ZJU-X99 exhibits rapid adsorption kinetics (1 min), high adsorption capacity (263 mg/g), and exceptional selectivity for Sr²⁺ even when 1000-fold of Na⁺, K⁺ and Cs⁺ coexist. Relative to alkali metals, Sr²⁺ ions are intricately ensconced within the supramolecular trap, resulting in lowest binding energy and minimal structural alterations. Dynamic column experiments and radioactive ⁹⁰Sr decontamination trials further validate its practical application prospects. Our findings offer valuable insights into the design of supramolecular frameworks featuring tailored binding sites for targeted ions.</p>