Dimension Control in Mixed Linker Metal-Organic Frameworks via Adjusting the Linker Shapes

In this context, we describe a novel method to control the dimensionality and, further, the morphology in three mixed linker metal-organic frameworks (MOFs) TMU-70, TMU-71, and TMU-49 via altering the linker shapes. The compatibility between the shape of linkers used in the mixed linker framework, specifically linker angles, can directly affect the dimensionality of the resulting networks from 2D to 3D. Using incompatible linkers (one bent and one linear) together with binodal SBU directed the structure to form 2D networks, while 3D networks were obtained through applying linkers with the same shape. Further, the 2D and 3D MOFs were fabricated through the coordination modulation strategy. The impact of various modulators on the size and morphology of the structures has been examined. The 2D MOFs produced only nanorods through application of different capping agents owing to their preferred crystal growth, while the 3D networks led to rod and plate morphologies. Also, the catalytic performance of MOFs in an aldol-type condensation reaction was estimated. High and fast catalytic activity is detected in nanoscale rod-shaped catalysts.

CO Guest Interactions in SDB-Based Metal-Organic Frameworks: A Solid-State Nuclear Magnetic Resonance Investigation

Metal-organic frameworks (MOFs) are promising materials for greener carbon monoxide (CO) capture and separation processes. SDB-based (SDB = 4,4^'-sulfonyldibenzoate) MOFs are particularly attractive due to their remarkable gas adsorption capacity under humid conditions. However, to the best of our knowledge, their CO adsorption abilities have yet to be investigated. In this report, CO-loaded PbSDB and CdSDB were characterized using variable-temperature (VT) ¹³C solid-state nuclear magnetic resonance (SSNMR) spectroscopy. These MOFs readily captured CO, with the adsorbed CO exhibiting dynamics as indicated by the temperature-dependent changes in the SSNMR spectra. Spectral simulations revealed that the CO simultaneously undergoes a localized wobbling about the adsorption site and a nonlocalized hopping between adjacent adsorption sites. The wobbling and hopping angles were also found to be temperature-dependent. From the appearance of the VT spectra and the extracted motional data, the CO adsorption mechanism was concluded to be analogous to that of CO₂. To gain a better understanding on the gas adsorption properties of these MOFs and their CO capture abilities, we subsequently compared the motional data to those reported for CO₂ in SDB-based MOFs and CO in MOF-74, respectively. A significant contrast in adsorption strength was observed in both cases because of the different physical properties of the guests (i.e., CO vs CO₂) and the MOF frameworks (i.e., SDB-based MOFs vs MOFs with open metal sites). Our results demonstrate that SSNMR spectroscopy can be employed to probe variations in binding behavior.

Elucidation of the Structural Origins and Contrasting Guest-Host Interactions in CO2 -Loaded CdSDB and PbSDB Metal-Organic Frameworks at High Pressures

PbSDB and CdSDB (SDB=4,4'-sulfonyldibenzoate) are two structurally related SDB-based metal-organic frameworks (MOFs) that demonstrate promising potential for selective CO₂ adsorption capabilities. The structural stabilities and guest-host interactions between CO₂ and PbSDB or CdSDB frameworks at high pressures up to 13 GPa in situ were comparatively investigated by Raman spectroscopy, FTIR spectroscopy, and synchrotron X-ray diffraction. Although both empty frameworks exhibited high chemical stabilities upon compression, they show different pressure-induced modifications in crystallinity. This difference can be attributed to their different coordination topologies that result in near isotropic contraction of unit cells for the CdSDB framework but anisotropic for the PbSDB framework. Furthermore, the CO₂ -loaded PbSDB and CdSDB frameworks at high pressures show strongly contrasting guest-host interactions in terms of the pressure-regulated CO₂ adsorption sites. In both frameworks, pressure can highly efficiently promote the formation of new CO₂ adsorption sites and the enhancement of guest-host interactions. In the CO₂ -loaded PbSDB framework, in particular, the peculiar pressure-tuned CO₂ population was observed preferentially on one of the two adsorption sites in response to external compression. These unique guest-host interaction behaviors can also be unambiguously correlated to their different topological origins. These findings for the PbSDB and CdSDB frameworks provide in-depth understanding of the structure-property relationship, which is of fundamental importance for CO₂ storage application in SDB-based MOFs.

Porous Zr6L3 Metallocage with Synergetic Binding Centers for CO2

Coordination-driven assembly has been widely successful in the synthesis of metallocages and used for many applications, such as catalysis. However, studies on CO₂ adsorption with metallocages have been rarely conducted, compared to other well-known cage-type materials, such as porous organic cages. In this study, a rational choice of ligand and metal led to the synthesis of a Zr₆L₃-type metallocage, exhibiting exceptional CO₂ adsorption properties. CO₂ adsorption experiments revealed that the metallocage shows highly selective adsorption of CO₂ over N₂ with high CO₂ binding energy. Density functional theory calculations uncovered the origin of this exceptional affinity for CO₂ over N₂.

Assembly of ZnII-coordination polymers constructed from benzothiadiazole functionalized bipyridines and V-shaped dicarboxylic acids: topology variety, photochemical and visible-light-driven photocatalytic properties

Photocatalytic properties of four benzothiadiazole functionalized coordination polymers have been reported.

Creation of new guest accessible space under gas pressure in a flexible MOF: multidimensional insight through combination of in situ techniques

Creation of a new guest accessible space under gas pressure in a flexible MOF studied by in situ single crystal diffraction and Pressure Gradient DSC.

Direct structural evidence of commensurate-to-incommensurate transition of hydrocarbon adsorption in a microporous metal organic framework

The efficiency of physisorption-based separation of gas-mixtures depends on the selectivity of adsorbent which is directly linked to size, shape, polarizability and other physical properties of adsorbed molecules. Commensurate adsorption is an interesting and important adsorption phenomenon, where the adsorbed amount, location, and orientation of an adsorbate are commensurate with the crystal symmetry of the adsorbent. Understanding this phenomenon is important and beneficial as it can provide vital information about adsorbate-adsorbent interaction and adsorption-desorption mechanism. So far, only sporadic examples of commensurate adsorption have been reported in porous materials such as zeolites and metal organic frameworks (MOFs). In this work we show for the first time direct structural evidence of commensurate-to-incommensurate transition of linear hydrocarbon molecules (C₂-C₇) in a microporous MOF, by employing a number of analytical techniques including single crystal X-ray diffraction (SCXRD), in situ powder X-ray diffraction coupled with differential scanning calorimetry (PXRD-DSC), gas adsorption and molecular simulations.

Metal–organic frameworks based on flexible ligands (FL-MOFs): structures and applications

This review presents the recent developments on FL-MOFs, including their structures and applications in gas adsorption, catalysis and proton conduction.

Evaluation of structural transformation in 2D metal–organic frameworks based on a 4,4′-sulfonyldibenzoate linker: microwave-assisted solvothermal synthesis, characterization and applications

Structural transformation has been observed in 2D MOFs.

Six new coordination polymers based on a tritopic pyridyldicarboxylate ligand: structural, magnetic and sorption properties

Using a rigid ligand, pyridine-3,5-bis(phenyl-4-carboxylic) acid, six new coordination polymers have been synthesized and characterized, and their magnetic, photoluminescence and gas adsorption properties have been studied.