25 Years of Reticular Chemistry Freund, Ralph; Canossa, Stefano; Cohen, Seth M. ...
Angewandte Chemie International Edition,
November 2, 2021, Volume:
60, Issue:
45
Journal Article
Peer reviewed
Open access
At its core, reticular chemistry has translated the precision and expertise of organic and inorganic synthesis to the solid state. While initial excitement over metal–organic frameworks (MOFs) and ...covalent organic frameworks (COFs) was undoubtedly fueled by their unprecedented porosity and surface areas, the most profound scientific innovation of the field has been the elaboration of design strategies for the synthesis of extended crystalline solids through strong directional bonds. In this contribution we highlight the different classes of reticular materials that have been developed, how these frameworks can be functionalized, and how complexity can be introduced into their backbones. Finally, we show how the structural control over these materials is being extended from the molecular scale to their crystal morphology and shape on the nanoscale, all the way to their shaping on the bulk scale.
Reticular chemistry translates the precision and expertise of organic and inorganic synthesis to the solid state. The most profound innovation of the field has been the elaboration of design strategies for the synthesis of extended crystalline solids through strong directional bonds. This Review highlights the classes of reticular materials, their functionalization, and the introduction of complexity into their backbones.
Metal‐organic frameworks (MOFs) are a class of porous materials with high surface areas, which are acquiring rapid attention on an exponential basis. A significant characteristic of MOFs is their ...ability to act as adsorbents to selectively separate component mixtures of similar size, thereby addressing the technological need for an alternative approach to conventional distillation methods. Recently, MOFs comprising a 3‐Dimensional (3D) linker have shown outstanding capabilities for difficult separations compared to the parent 2‐Dimensional (2D) analogue. 3D‐linkers with a polycyclic core are underrepresented in the MOF database due to the widespread preferred use of 2D‐linkers and the misconceived high‐cost of 3D linkers. We summarize the recent research of 3D‐linker MOFs and highlight their beneficial employment for selective gas and hydrocarbon adsorption and separation. Furthermore, we outline forecasts in this area to create a platform for widespread adoption of 3D‐linkers in MOF synthesis.
Increasing linker dimensionality in metal‐organic frameworks limits the effects of linker orientation and structural flexibility on pore size, ultimately enhancing the separation capabilities of these materials.
Effective solid-state adsorbent materials, such as metal organic frameworks (MOFs), rely upon tailored void spaces for selective adsorption of one component from a mixture. This is particularly ...crucial when separating challenging mixtures such as benzene (Bz) and cyclohexane (Cy) requiring a highly expensive and energy intensive process. Employing bulky “3D-linkers” to construct MOFs leads to materials with unique, contoured pore shapes which consequently allow for significant control over guest adsorption preferences. Investigation into these selectivity preferences is key to identifying suitable materials for industrial separations and is an area currently underexplored. Here, we provide an in-depth investigation exploring the selectivity path between planar and 3D-linkers and their preference to adsorb either Cy or Bz. To validate this principle, the adsorption selectivity of Cy and Bz in 3DL-MOF-1 (Zn4O(pdc)3 (pdc = bicylo1.1.1pentane-1,3-dicarboxylate), CUB-5, and MOF-5 was explored. MOF-5 exhibits a selective preference for Cy adsorption at low pressures, contrary to popular belief, while CUB-5 and 3DL-MOF-1 are Bz selective. DFT-D3 calculations and breakthrough simulations explore this behavior and highlight CUB-5 and MOF-5 as strong candidates for future separation materials.
Investigating the impact of ligand functionalization on the gas separation performance of metal–organic frameworks (MOFs) is important because it provides valuable insights into the design and ...architectures of high-performance materials. Here, we report five new MOFs that are derivatives of MUF-15. They adopt the general formula Co6(μ3-OH)2(ipa-X)5(H2O)2, where ipa-X is a 5-substituted isophthalate linker with a fluoro, hydroxyl, bromo, nitro, or methyl substituent, and are denoted as MUF-15-X. MUF-15-F and MUF-15-NO2 are isoreticular to MUF-15, while MUF-15-Br and MUF-15-CH3 are closely related isomers of the MUF-15 topology. The frameworks exhibit various degrees of structural stability. The methyl group confers high moisture stability on the framework, while the hydroxyl group results in low stability. The chemical characteristics and dimensions of the framework pores are influenced by the functional group, resulting in distinct differences in gas sorption and separation performance. The nitro-functionalized framework is flexible upon the adsorption of certain gases, notably CO2 and ethane. We examined the effectiveness of these materials for the separations of C2H6/C2H4, C2H4/C2H2, and C2H2/CO2 and found that the functional groups can invert the selectivity of MUF-15 toward these gas pairs.
Hydrogen-bonded frameworks were prepared from a tetra-amidinium component and three-dimensional cubane and bicyclopentane dicarboxylate linkers. Despite the incorporation of aliphatic components, the ...frameworks demonstrate strong and reversible uptake of water vapour, with one of the frameworks showing water uptake at very low relative humidity.
Cubane and bicyclopentane dicarboxylates are used to prepare porous hydrogen-bonded frameworks that show high-capacity water vapour sorption.
The high surface area and porosity, and limitless compound and network combinations between the metal ions and organic ligands making up metal-organic frameworks (MOFs) offer tremendous opportunities ...for their use in many applications. While numerous methods have been proposed for the synthesis of MOF powders, it is often difficult to obtain oriented crystals with these techniques. Further, the need for additional post-synthesis steps to activate the crystals and release them from the substrate presents a considerable production challenge. Here, we report an acoustically-driven microcentrifugation platform that facilitates fast convective solutal transport, allowing the synthesis of MOF crystals in as short as five minutes. The crystals are not only oriented due to long-range out-of-plane superlattice ordering aided by molecular dipole polarization under the acoustoelectric coupling, but also simultaneously activated during the synthesis process.
We highlight two key examples of where the achirality of reagents used in MOF syntheses transposes to chiral structures, thereby expanding the potential ligand pool used in the future design of ...chiral MOFs. Herein, we report the characterisation of two new chiral Cd
II
MOFs: (1) a pair of enantiomorphous structures produced from the achiral bicyclo1.1.1pentane-1,3-dicarboxyate linker, Cd(pdc)(DMF) (pdc = bicyclo1.1.1pentane-1,3-dicarboxylate; DMF =
N
,
N
-dimethylformamide) (
3DL-MOF-3
), and (2) a similar chiral network featuring cubane-1,4-dicarboxylate, Cd
3
(cdc)
3
(DMF)
3
(cdc = cubane-1,4-dicarboxylate) (
3DL-MOF-4
). Conventional solvothermal synthesis of
3DL-MOF-3
yields a conglomerate of two enantiomorphs that spontaneously resolve into their respective right- or left-handed chiral hexagonal space groups (space groups
P
6
1
/
P
6
5
). Similarly,
3DL-MOF-4
resolves into a non-centrosymmetric orthorhombic phase (
P
2
1
2
1
2). Both
3DL-MOF-3
and
3DL-MOF-4
possess infinitely-linked, chiral, and 1D Cd-O helical chains which are observed to be the apparent cause of chirality in each system. In both cases, homochirality is preserved within each individual crystal where only one type of helical handedness is observed. We consider a general mechanism for this preservation of homochirality to include an avoidance of a physical analogue of geometric frustration which manifests due to the tripartite nature of the underlying triangular lattice upon which each chiral chain is located.
Two chiral metal-organic frameworks that are differentiated by their Cd-centred helical twists are prepared by spontaneous chiral resolution from rigid, aliphatic, and achiral precursors.
Zinc norcorrole was prepared as its pyridine complex (ZnNc·pyridine) by metalation of freebase norcorrole. The ZnNc·pyridine complex is distinctly bowl-shaped, as demonstrated by both X-ray ...crystallography and nuclear magnetic resonance (NMR) spectroscopy. NMR spectroscopy showed characteristic ring current deshielding effects, with different magnitudes on either face of the bowl-shaped complex. Exchanging the pyridine ligand with the bidentate ligand DABCO results in the formation of a stable (ZnNc)2·DABCO sandwich complex, which was also characterized by crystallography and NMR spectroscopy. The NMR resonances of the axial ligands in all of the complexes demonstrate that the paratropic ring current in zinc norcorrole is approximately 40 nA/T, which is comparable in magnitude to the diatropic ring current in porphyrin. Analysis of the ligand-exchange processes on addition of DABCO to ZnNc·pyridine showed that ZnNc coordinates to axial nitrogen-containing ligands with approximately 1000-fold higher binding constants than analogous zinc porphyrins.
One prominent aspect of metal organic frameworks (MOFs) is the ability to tune the size, shape, and chemical characteristics of their pores. MOF-5, with its open cubic connectivity of Zn4O clusters ...joined by two-dimensional, terephthalate linkers, is the archetypal example: both functionalized and elongated linkers produce isoreticular frameworks that define pores with new shapes and chemical environments. The recent scalable synthesis of cubane-1,4-dicarboxylic acid (1,4-H2cdc) allows the first opportunity to explore its application in leading reticular architectures. Herein we describe the use of 1,4-H2cdc to construct Zn4O(1,4-cdc)3, referred to as CUB-5. Isoreticular with MOF-5, CUB-5 adopts a cubic architecture but features aliphatic, rather than aromatic, pore surfaces. Methine units point directly into the pores, delivering new and unconventional adsorption locations. Our results show that CUB-5 is capable of selectively adsorbing high amounts of benzene at low partial pressures, promising for future investigations into the industrial separation of benzene from gasoline using aliphatic MOF materials. These results present an effective design strategy for the generation of new MOF materials with aliphatic pore environments and properties previously unattainable in conventional frameworks.
Metal–organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules ...with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo1.1.1pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different sizes and shapes of these isomers.
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