Metal–Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal–Organic Framework

We report a hafnium-containing MOF, hcp UiO-67­(Hf),
which is a ligand-deficient layered analogue of the face-centered
cubic fcu UiO-67­(Hf). hcp UiO-67 accommodates
its lower ligand:metal ratio compared to fcu UiO-67 through
a new structural mechanism: the formation of a condensed “double
cluster” (Hf12O8(OH)14), analogous
to the condensation of coordination polyhedra in oxide frameworks.
In oxide frameworks, variable stoichiometry can lead to more complex
defect structures, e.g., crystallographic shear planes or modules
with differing compositions, which can be the source of further chemical
reactivity; likewise, the layered hcp UiO-67 can react
further to reversibly form a two-dimensional metal–organic
framework, hxl UiO-67. Both three-dimensional hcp UiO-67 and two-dimensional hxl UiO-67 can be delaminated
to form metal–organic nanosheets. Delamination of hcp UiO-67 occurs through the cleavage of strong hafnium-carboxylate
bonds and is effected under mild conditions, suggesting that defect-ordered
MOFs could be a productive route to porous two-dimensional materials.