Structural Diversity of Zirconium Metal–Organic Frameworks and Effect on Adsorption of Toxic Chemicals

Abstract

While linkers with various conformations pose challenges in the design and prediction of metal–organic framework (MOF) structures, they ultimately provide great opportunities for the discovery of novel structures thereby enriching structural diversity. Tetratopic carboxylate linkers, for example, have been widely used in the formation of Zr-based MOFs due to the ability to target diverse topologies, providing a promising platform to explore their mechanisms of formation. However, it remains a challenge to control the resulting structures when considering the complex assembly of linkers with unpredicted conformations and diverse Zr6 node connectivities. Herein, we systematically explore how solvents and modulators employed during synthesis influence the resulting topologies of Zr-MOFs, choosing H4TCPB-Br2 (1,4-dibromo-2,3,5,6-tetrakis­(4-carboxyphenyl)­benzene) as a representative tetratopic carboxylate linker. By modulating the reaction conditions, the conformations of the linker and the connectivities of the Zr6 node can be simultaneously tuned, resulting in four types of structures: a new topology (NU-500), she (NU-600), scu (NU-906), and csq (NU-1008). Importantly, we have synthesized the first 5-connected Zr6 node to date with the (4,4,4,5)-connected framework, NU-500. We subsequently performed detailed structural analyses to uncover the relationship between the structures and topologies of these MOFs and demonstrated the crucial role that the flexible linker played to access varied structures by different degrees of linker deformation. Due to a variety of pore structures ranging from micropores to hierarchical micropores and mesopores, the resulting MOFs show drastically different behaviors for the adsorption of n-hexane and dynamic adsorption of 2-chloroethyl ethyl sulfide (CEES) under dry and humid conditions.

A Zirconium Metal-Organic Framework with SOC Topological Net for Catalytic Peptide Bond Hydrolysis

“…Zr6-oxo cluster is the dominant building unit in the fabrication of Zr-carboxylate MOFs. The connection numbers of Zr6-oxo clusters cover a wide range of 12, 10, 9, 8, 6, 5 and 4 in the reported examples, showing an extraordinary flexibility in connecting various linkers to generate a large library of different structures 13,14,15,16 . While the stabilities of Zr-MOFs constructed with low connection-number (5, and 4) nodes are still under debate 15,16,17,18 , 6-connection is likely the limit to keep the material stability at an acceptable level toward certain applications 19,20,21 .…”

“…The connection numbers of Zr6-oxo clusters cover a wide range of 12, 10, 9, 8, 6, 5 and 4 in the reported examples, showing an extraordinary flexibility in connecting various linkers to generate a large library of different structures 13,14,15,16 . While the stabilities of Zr-MOFs constructed with low connection-number (5, and 4) nodes are still under debate 15,16,17,18 , 6-connection is likely the limit to keep the material stability at an acceptable level toward certain applications 19,20,21 . In a sharp contrast to the large number of Zr-MOFs based on high connection-number (above till 12) building units, only six compounds are constructed from 6connected Zr6-oxo clusters, including PCN-224 22 , PCN-777 23 (PCN, Porous Coordination Network), UMCM-309 24 (UMCM, University of Michigan Crystalline Material), the interpenetrated Zr-BTB 25 , MOF-808 19 and BUT-108 (BUT, Beijing University of Technology) 26 .…”

Zr-MOFs for CF4/CH4, CH4/H2, and CH4/N2 separation: towards the goal of discovering stable and effective adsorbents

“…Metal-organic frameworks (MOFs) are nanoporous, crystalline structures offering tunable chemical environments which can be exploited for various applications including gas storage/separation, catalysis, sensing, drug delivery, etc. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] While they possess favorable structural features namely high porosity, ease of functionalization, adjustable pore sizes, etc., many of them suffer from relatively lower thermal, hydrothermal, and/or chemical stability than industrially utilized zeolites. [15][16][17][18] Among different subclasses of MOFs, Zr-MOFs have garnered particular interest as some of them have been shown to exhibit good stability at high temperatures, in humid conditions, and/or acidic/basic environments.…”

Designing Oxide Aerogels With Enhanced Sorptive and Degradative Activity for Acute Chemical Threats

“…Modifications to render MOFs more water-stable, such as exchanging organic linkers or varying the metal center, may come at the expense of filtration performance (DeCoste and Son et al, 2020;Song et al, 2020). Figure 2 highlights the stark contrast in uptake of selected MOFs under dry (0% RH) vs. humid (80% RH) conditions (Chen et al, 2020). Furthermore, during CW agent hydrolysis certain Zr-based MOFs form tightly bound products that render them ineffective as gas-phase catalysts (Wang et al, 2017a).…”