Sequential Oriented Growth of Zr-fcu-MOFs on Different Crystal Facets of MIL-96(Al)

The oriented growth between topologically distinct metal-organic frameworks (MOFs) opens new opportunities for accessing unique MOF-on-MOF structures and material properties. However, current examples only explored the growth of a guest MOF on the most thermodynamically favored crystal facet of a template MOF, which greatly limited the structural diversity. We report here the first example of sequential oriented growth of two cubic MOFs, UiO-66 and UiO-67, on a hexagonal MOF, MIL-96(Al). We found that UiO-66 crystals preferably grew on the top and bottom faces of MIL-96(Al) through its {111} facets and then on the less-favored side crystal faces through its {001} facets in order of priority. Interestingly, when UiO-66 was replaced by its isoreticular structural analogue, UiO-67, the growth sequence became dependent on the modulator concentration. At a low modulator concentration, the top and bottom faces of MIL-96(Al) were still the most favored growth sites for UiO-67, whereas at a high modulator concentration, the equatorial belt was the most preferred growth site. With a moderate amount of modulator, UiO-67 crystals can be found directionally grown on all three different exposed crystal facets of MIL-96(Al). Further analysis of the underlying lattice uncovered the delicate interplay between lattice mismatch and modulator adsorption at the MOF-MOF interface in determining the growth sequence and orientation of the MOF-on-MOF structures. This example highlights the potential of using sequential oriented growth on multiple crystal facets to access complex MOF-on-MOF structures.

Automated summary

Exploring oriented growth between different metal-organic frameworks offers new opportunities to access complex MOF-on-MOF structures, with the growth sequence and orientation being influenced by factors such as modulator concentration and lattice mismatch.