Nanoporous Designer Solids with Huge Lattice Constant Gradients: Multiheteroepitaxy of Metal-Organic Frameworks

We demonstrate the realization of hierarchically organized MOF (metal organic framework) multilayer systems with pronounced differences in the size of the nanoscale pores. Unusually large values for the lattice constant mismatch at the MOF MOF heterojunctions are made possible by a particular liquid-phase epitaxy process. The multiheteroepitaxy is demonstrated for the isoreticular SURMOF-2 series [Liu et al. Sci. Rep. 2012, 2, 921] by fabricating trilayer systems with lattice constants of 1.12, 1.34, and 1.55 nm. Despite these large (20%) lattice mismatches, highly crystalline, oriented multilayers were obtained. A thorough theoretical analysis of the MOF-on-MOF heterojunction structure and energetics allows us to identify the two main reasons for this unexpected tolerance of large lattice mismatch: the healing of vacancies with acetate groups and the low elastic constant of MOF materials.