Rational tuning of thorium–organic frameworks by reticular chemistry for boosting radionuclide sequestration

The reticular chemistry strategy presents a powerful molecule-design tool to tailor the physical and chemical properties of metal–organic framework (MOF). In this work, we for the first time investigated the effect of organic ligands on the radionuclide sequestration (TcO₄⁻) of thorium–organic framework. Through a coordination modulation technique, two novel isoreticular thorium–organic frameworks, namely Th-MOF-67 and Th-MOF-68, were obtained. Relative to the antetype MOF of Th-MOF-66 that shows extremely low uptake of ReO₄⁻ (a chemical surrogate of radioactive TcO₄⁻), the isoreticular MOFs of Th-MOF-67 and Th-MOF-68 enable ultrahigh uptake of ReO₄⁻, giving an impressively 36.8-fold or 56-fold enhancement, respectively. The adsorption capacity of Th-MOF-68 is as high as 560 mg/g, exceeding most reported adsorbents for such use. The mechanism for such exceptional outstanding performance, as unveiled by both the single crystal X-ray diffraction and theoretical calculation, is due to coordination interaction for Th-MOF-67, when a tetrazolate ligand was used, or a combined effect from both coordination interaction and anion-exchange for Th-MOF-68, if using a triazolate ligand.