Mechanochemical synthesis of phase-pure zirconium metal–organic cages

Abstract

Zirconium metal–organic cages (Zr-MOCs) exhibit promising applications in adsorption and molecular separation, thanks to their high porosity, stability, and solution processability. However, their synthesis relies on traditional solvothermal methods. In this work, we developed a mechanochemical synthetic route for Zr-MOCs by milling pre-formed Zr-clusters with terephthalic acid. The Zr₃-cluster is easily prepared by combining zirconocene dichloride with carboxylic acids such as acetic acid and benzoic acid. Typical yields of 70% were achieved in only 30 minutes, using a minimal amount of DMF (η = 0.5 µL g⁻¹). This kinetically controlled strategy produces phase-pure tetrahedral cages with high surface area (>450 m² g⁻¹), comparable to those produced by conventional solvothermal processes. The method enables tunable cage architectures by varying ligand identity. The successful synthesis of Zr-MOCs with mono- and bi-functional bidentate ligands, as well as tri-dentate ligands, was achieved, demonstrating the versatility of the mechanochemical approach. This work opens new possibilities for the preparation of Zr-MOCs with insoluble ligands and facilitates scalable production.