Solvent-free mechanochemistry for the preparation of mixed-ligand cuboctahedral porous coordination cages

Abstract

This study investigates post-synthetic ligand exchange in a series of copper(II) and chromium(II) cuboctahedral cages of the formula M₂₄(R-bdc)₂₄ through solvent-free mechanochemistry for the preparation of mixed-ligand cages. While solvent-based ligand exchange does not proceed when the cages are insoluble or when they are dissolved in non-coordinating solvents, solvent-free mechanochemistry can be used to prepare a number of mixed-ligand cages featuring a variety of functional groups regardless of cage solubility. We further extend this strategy to intercage ligand exchange reactions where the solid-state reaction of cages proceeds in just ten minutes while corresponding solvent-based reactions require more than one week of reaction time. The results highlight mechanochemically-facilitated ligand exchange as an exceptionally facile and efficient method for the production of mixed-ligand cuboctahedral cages.