Halogen hydrogen-bonded organic framework (XHOF) constructed by singlet open-shell diradical for efficient photoreduction of U(VI)

While hydrogen bonded organic frameworks are well covered in the scientific literature, halogen hydrogen-bonded organic framework (XHOF) remain less explored. Here, the authors demonstrate a highly stable diradical-based XHOF and demonstrate photoreduction of uranyl ions and high capacity of uranyl immobilization. Synthesis of framework materials possessing specific spatial structures or containing functional ligands has attracted tremendous attention. Herein, a halogen hydrogen-bonded organic framework (XHOF) is fabricated by using Cl- ions as central connection nodes to connect organic ligands, 7,7,8,8-tetraaminoquinodimethane (TAQ), by forming a Cl-center dot center dot center dot H-3 hydrogen bond structure. Unlike metallic node-linked MOFs, covalent bond-linked COFs, and intermolecular hydrogen bond-linked HOFs, XHOFs represent a different kind of crystalline framework. The electron-withdrawing effect of Cl- combined with the electron-rich property of the organic ligand TAQ strengthens the hydrogen bonds and endows XHOF-TAQ with high stability. Due to the production of excited electrons by TAQ under light irradiation, XHOF-TAQ can efficiently catalyze the reduction of soluble U(VI) to insoluble U(IV) with a capacity of 1708 mg-U g(-1)-material. This study fabricates a material for uranium immobilization for the sustainability of the environment and opens up a new direction for synthesizing crystalline framework materials.

Automated summary

While hydrogen-bonded organic frameworks are well-studied, halogen hydrogen-bonded organic frameworks (XHOF) remain less explored. The authors have demonstrated a highly stable XHOF and its potential for photocatalytic reduction of uranyl ions, suggesting a new direction for synthesizing crystalline framework materials.