Developing efficient mechanochemical routes to porous metal-organic polyhedra, supported by 3D electron diffraction

Metal-organic polyhedra (MOPs) are the porous molecular counterparts to metal-organic frameworks (MOFs). While mechanochemistry has been successfully applied to a wide range of MOFs, this synthetic approach has found more limited use for MOPs. Herein, two mechanochemical routes have been developed for a series of MOPs presenting a lantern geometry. The cages can be formed through: Route 1, grinding with DMA, and therefore achieving a reduction in solvent usage of 90%; or through Route 2, grinding with MeOH to completely eliminate the use of non-volatile, highly toxic solvents. The development of Route 2 is facilitated by 3D electron diffraction, which proved the formation of discrete cages that would otherwise be inaccessible through direct solvothermal synthesis. In all cases, the degree of crystallinity of the mechanochemical products is equal or superior to material obtained through solvothermal methods, and exhibits comparable porosity. As well as presenting a method to improve the sustainability of the synthesis of these cages, this work extends the range of porous cages to which mechanochemistry can be applied. Given the known dependence of the porosity of MOPs on the crystal packing of their parent solvated forms, Route 2 suggests that future work could probe the formation of new solvated phases that display distinct gas sorption behaviour.