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

Matthew J Cliffe,Alexander C Forse,Yue Wu,Francesca C N Firth,Ben Slater,David Fairen-Jimenez,Oxana V Magdysyuk,Joshua A Hill,Michael W Gaultois,Jeongjae Lee,Clare P Grey,Elizabeth Castillo-Martínez,Peyman Z Moghadam,Andrew L Goodwin

doi:10.1021/jacs.7b00106

Abstract

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.

Highlights

In many inorganic functional materials, compositional flexibility is facilitated not just by inclusion of vacancies and through the formation of higher-dimensionality defects, such as stacking faults, dislocations, or crystallographic shear planes
We further show that both hcp and hxl UiO-67 can be delaminated into metal−organic nanosheets, demonstrating a new route to porous 2D materials, and characterize these new phases and explain their reactivity using a combination of powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), pair distribution function (PDF) analysis, and quantumchemical calculations
Structure solution from laboratory PXRD data revealed a hexagonal 3D Metal−organic frameworks (MOFs) consisting of an hcp array of Hf12O8(OH)[14] clusters connected by bpdc2− ligands (Figure 1b,c)

Summary

Introduction

In many inorganic functional materials, compositional flexibility is facilitated not just by inclusion of vacancies and through the formation of higher-dimensionality defects, such as stacking faults, dislocations, or crystallographic shear planes. Metal−organic frameworks (MOFs) are framework materials that consist of nodes of metal atoms or clusters linked together by organic molecular ligands. They are materials of great current interest, in particular because of their unique and tailorable porosities, which facilitate applications as wideranging as gas separation and storage, selective catalysis, and drug delivery. Along with multicomponent MOFs,[10] particular attention has been paid to the preparation and characterization of materials containing point defects, principally ligand and metal-cluster vacancies.[8,11] These vacancies reduce the overall density of the material ( increasing the porosity) and

Methods

Results

Conclusion