Efficient iodine capture by metal–organic cubes based on hexanuclear vanadium clusters

Abstract

The cube is the only regular hexahedron among the Platonic solids, but supramolecules with a cubic configuration have rarely been reported. Herein, two isostructural metal–organic cubes VMOC-6 and VMOC-7 with large cavities are successfully synthesized by face-directed self-assembly of concave hexanuclear vanadium clusters [V₆O₆(OCH₃)₉(XO₄)(COO)₃]ⁿ⁻ (X = S, n = 2; X = V, n = 1) and large-size nitrogen-containing tetravalent ligands. VMOC-6 and VMOC-7 are the largest metal–organic cubes based on metal clusters with an outer diameter of 28.47 × 28.17 × 28.44 ų and an inner cavity volume of 7785.657 ų. Moreover, the cages can capture volatile iodine vapor with an uptake value of up to 1.83 g g⁻¹, which is superior to those of most metal–organic materials. Mechanistic studies have shown that their good adsorption capacity is closely related to the presence of large internal cavities, electron-donating pyridine groups and redox-active V sites. The present work shows the potential application of these mesoporous MOPs in the treatment of iodine-containing nuclear waste.