Single crystalline hollow metal-organic frameworks: a metal-organic polyhedron single crystal as a sacrificial template

Abstract

We report for the first time the preparation of single crystalline hollow MOFs with the pore dimension of the MOF shell in the order of nanometer and the hollow cavity dimension in the order of micrometer using a metalorganic polyhedron (MOP) single crystal as a sacrificial hard template. Hollow MOFs based on cuboctahedral CuMOP can be obtained via a stepwise synthetic approach. After the preparation of single crystals of cuboctahedral CuMOP with dimensions in the order of several micrometers and several hundred micrometers made of approximately 3 nm MOP building units, single MOP crystals were used as hard sacrificial templates. During a stepwise process, the single MOP crystals serve not only as a hard template, but also as a reactant for the single crystalline hollow MOF. The optical microscopic images of the fragmented hollow MOF crystals with several hundred micrometers clearly show the hollow nature of the MOF crystals. The hollow nature of the MOF crystals with several micrometers was confirmed by using FIB-SEM images of the hollow crystals sliced by Ga ion milling. This work demonstrates a strategy for the bulk preparations of single crystalline hollow MOFs.