Muwei Zhang

Symmetry-Guided Synthesis of Highly Porous Metal–Organic Frameworks with Fluorite Topology

Two stable, non-interpenetrated MOFs, PCN-521 and PCN-523, were synthesized by a symmetry-guided strategy. Augmentation of the 4-connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8-connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN-521 has the largest BET surface area (3411 m(2) g(-1)), pore size (20.5×20.5×37.4 Å) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non-interpenetrated MOFs with high porosity.

Rational design of metal–organic frameworks with anticipated porosities and functionalities

Metal–organic frameworks have emerged as a new category of porous materials that have intriguing structures and diverse applications. Even though the early discovery of new MOFs appears to be serendipitous, much effort has been made to reveal their structure–property relationships for the purpose of rationally designing novel frameworks with expected properties. Until now, much progress has been made to rationalize the design and synthesis of MOFs. This highlight review will outline the recent advances on this topic from both our and other groups and provide a systematic overview of different methods for the rational design of MOFs with desired porosities and functionalities. In this review, we will categorize the recent efforts for rational MOF design into two different approaches: a structural approach and a functional approach.

Increasing the Stability of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a new category of advanced porous materials undergoing study by many researchers for their vast variety of both novel structures and potentially useful properties arising from them. Their high porosities, tunable structures, and convenient process of introducing both customizable functional groups and unsaturated metal centers have afforded excellent gas sorption and separation ability, catalytic activity, luminescent properties, and more. However, the robustness and reactivity of a given framework are largely dependent on its metal-ligand interactions, where the metal-containing clusters are often vulnerable to ligand substitution by water or other nucleophiles, meaning that the frameworks may collapse upon exposure even to moist air. Other frameworks may collapse upon thermal or vacuum treatment or simply over time. This instability limits the practical uses of many MOFs. In order to further enhance the stability of the framework, many different approaches, such as the utilization of high-valence metal ions or nitrogen-donor ligands, were recently investigated. This review details the efforts of both our research group and others to synthesize MOFs possessing drastically increased chemical and thermal stability, in addition to exemplary performance for catalysis, gas sorption, and separation.

Structural design of porous coordination networks from tetrahedral building units

Ligand design is of vital importance in the preparation of metal–organic frameworks (MOFs), and the rigid tetrahedral ligands are especially interesting due to their fully extended nature and diverse symmetric elements. In this work, a synthetically accessible silicon-centered tetrahedral ligand was prepared from inexpensive starting materials and eight MOFs were obtained from different solvothermal reactions. All the MOFs were structurally characterized and are inherently porous with solvent accessible volume up to 73.10%; while at least two of them possess a permanent inner porosity after the removal of any guest molecules in the framework. Among all these MOFs, seven of them possess a new structure, one of them possesses a novel topology, and two of them show properties potentially useful for gas storage applications. In particular, PCN-512 has a H2 uptake of 1.39 wt% at 77 K and 1.08 bar. This makes it a promising material for industrial gas storage applications because of both its low synthetic cost and its relatively large gas capacity. PCN-515 contains three distinctive rarely-seen secondary building units (SBUs) in the same framework, which makes it an unprecedented 4,4,4,4,4,5,7-connected network.

Design and synthesis of nucleobase-incorporated metal–organic materials

Two nucleobase-incorporated metal–organic materials were designed, synthesized and structurally characterized. PCN-530 is among the few examples of metal–organic frameworks that utilize adenine as a constructional unit, while TMOP-1 is the first existing example of a crystallographically characterized nucleobase-incorporated metal–organic polyhedron. This work also offers a general perspective for the design and synthesis of nucleobase-incorporated metal–organic materials.

Lithium inclusion in indium metal-organic frameworks showing increased surface area and hydrogen adsorption

Investigation of counterion exchange in two anionic In-Metal-Organic Frameworks (In-MOFs) showed that partial replacement of disordered ammonium cations was achieved through the pre-synthetic addition of LiOH to the reaction mixture. This resulted in a surface area increase of over 1600% in {Li [In(1,3 − BDC)2]}n and enhancement of the H2 uptake of approximately 275% at 80 000 Pa at 77 K. This method resulted in frameworks with permanent lithium content after repeated solvent exchange as confirmed by inductively coupled plasma mass spectrometry. Lithium counterion replacement appears to increase porosity after activation through replacement of bulkier, softer counterions and demonstrates tuning of pore size and properties in MOFs.

Pore-controlled formation of 0D metal complexes in anionic 3D metal–organic frameworks

The host–guest chemistry between a series of anionic MOFs and their trapped counterions was investigated by single crystal XRD. The PCN-514 series contains crystallographically identifiable metal complexes trapped in the pores, where their formation is controlled by the size and shape of the MOF pores. A change in the structure and pore size of PCN-518 indicates that the existence of guest molecules may reciprocally affect the formation of host MOFs.