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Metal–organic frameworks (MOFs) assembled from multiple building blocks exhibit greater chemical complexity and superior functionality in practical applications. Herein, we report a new approach based on using prefabricated cavities to design isoreticular multicomponent MOFs from a known parent MOF. We demonstrate this concept with the formation of multicomponent HKUST-1 analogues, using a prefabricated cavity that comprises a cuboctahedral Rh(II) metal–organic polyhedron functionalized with 24 carboxylic acid groups. The cavities are reticulated in three dimensions via Cu(II)-paddlewheel clusters and (functionalized) 1,3,5-benzenetricarboxylate linkers to form three- and four-component HKUST-1 analogues.

The metal-organic framework MOF-808 contains Zr6O8nodes with a high density of vacancy sites, which can incorporate carboxylate-containing functional groups to tune chemical reactivity. Although the postsynthetic methods to modify the chemistry of the Zr6O8nodes in MOFs are well known, tackling these alterations from a structural perspective is still a challenge. We have combined infrared spectroscopy experiments and first-principles calculations to identify the presence of node vacancies accessible for chemical modifications within the MOF-808. We demonstrate the potential of our approach to assess the decoration of MOF-808 nodes with different catechol–benzoate ligands. Furthermore, we have applied advanced synchrotron characterization tools, such as pair distribution function analyses and X-ray absorption spectroscopy, to resolve the atomic structure of single metal sites incorporated into the catechol groups postsynthetically. Finally, we demonstrate the catalytic activity of these MOF-808 materials decorated with single copper sites for 1,3-dipolar cycloadditions.

How molecules approach, bind at, and release from catalytic sites is key to heterogeneous catalysis, including for emerging metal–organic framework (MOF)-based catalysts. We use in situsynchrotron X-ray scattering analysis to evaluate the dominant binding sites for reagent and product molecules in the vicinity of catalytic Ni-oxo clusters in NU-1000 with different surface functionalization under conditions approaching those used in catalysis. The locations of the reagent and product molecules within the pores can be linked to the activity for ethylene hydrogenation. For the most active catalyst, ethylene reagent molecules bind close to the catalytic clusters, but only at temperatures approaching experimentally observed onset of catalysis. The ethane product molecules favor a different binding location suggesting that the product is readily released from the active site. An unusual guest-dependence of the framework negative thermal expansion is documented. We hypothesize that reagent and product binding sites reflect the pathway through the MOF to the active site and can be used to identify key factors that impact the catalytic activity.

Reticular chemistry has boosted the design of thousands of metal and covalent organic frameworks for unlimited chemical compositions, structures, and sizable porosities. The ability to generate porous materials at will on the basis of geometrical design concepts is responsible for the rapid growth of the field and the increasing number of applications derived. Despite their promising features, the synthesis of targeted homo- and heterometallic titanium–organic frameworks amenable to these principles is relentlessly limited by the high reactivity of this metal in solution that impedes the controlled assembly of titanium molecular clusters. We describe an unprecedented methodology for the synthesis of heterometallic titanium frameworks by metal-exchange reactions of MOF crystals at temperatures below those conventionally used in solvothermal synthesis. The combination of hard (titanium) and soft (calcium) metals in the heterometallic nodes of MUV-10(Ca) enables controlled metal exchange in soft positions for the generation of heterometallic secondary building units (SBUs) with variable nuclearity, controlled by the metal incorporated. The structural information encoded in the newly formed SBUs drives an MOF-to-MOF conversion into bipartite nets compatible with the connectivity of the organic linker originally present in the crystal. Our simulations show that this transformation has a thermodynamic origin and is controlled by the terminations of the (111) surfaces of the crystal. The reaction of MUV-10(Ca) with first-row transition metals permits the production of crystals of MUV-101(Fe,Co,Ni,Zn) and MUV-102(Cu), heterometallic titanium MOFs isostructural with archetypical solids such as MIL-100 and HKUST. In comparison to de novo synthesis, this metal-induced topological transformation provides control over the formation of hierarchical micro-/mesopore structures at different reaction times and enables the formation of heterometallic titanium MOFs not accessible under solvothermal conditions at high temperature, thus opening the door for the isolation of additional titanium heterometallic phases not linked exclusively to trimesate linkers.

Covalent organic frameworks (COFs) are commonly synthesized under harsh conditions yielding unprocessable powders. Control in their crystallization process and growth has been limited to studies conducted in hazardous organic solvents. Herein, we report a one-pot synthetic method that yields stable aqueous colloidal solutions of sub-20 nm crystalline imine-based COF particles at room temperature and ambient pressure. Additionally, through the combination of experimental and computational studies, we investigated the mechanisms and forces underlying the formation of such imine-based COF colloids in water. Further, we show that our method can be used to process the colloidal solution into 2D and 3D COF shapes as well as to generate a COF ink that can be directly printed onto surfaces. These findings should open new vistas in COF chemistry, enabling new application areas.

UiO-66, MOF-808and NU-1000metal–organic frameworks exhibit a differentiated reactivity toward [Mg(OMe)2(MeOH)2]4related to their pore accessibility. Microporous UiO-66remains unchanged while mesoporous MOF-808and hierarchical micro/mesoporous NU-1000materials yield doped systems containing exposed MgZr5O2(OH)6clusters in the mesoporous cavities. This modification is responsible for a remarkable enhancement of the catalytic activity toward the hydrolytic degradation of P–F and P–S bonds of toxic nerve agents, at room temperature, in unbuffered aqueous solutions.

Promoters are ubiquitous in industrial heterogeneous catalysts. The wider roles of promoters in accelerating catalysis and/or controlling selectivity are, however, not well understood. A model system has been developed where a heterobimetallic active site comprising an active metal (Rh) and a promoter ion (Ga) is preassembled and delivered onto a metal–organic framework (MOF) support, NU-1000. The Rh–Ga sites in NU-1000 selectively catalyze the hydrogenation of acyclic alkynes to E-alkenes. The overall stereoselectivity is complementary to the well-known Lindlar’s catalyst, which generates Z-alkenes. The role of the Ga in promoting this unusual selectivity is evidenced by the lack of semihydrogenation selectivity when Ga is absent and only Rh is present in the active site.

Schiff-condensation reactions carried out between 1,6-diaminopyrene (DAP) and the tritopical 1,3,5 benzenetricarbaldehyde (BTCA) or 2,4,6-triformylphloroglucinol (TP) ligands give rise to the formation of two-dimensional imine-based covalent-organic frameworks (COFs), named IMDEA-COF-1and -2, respectively. These materials show dramatic layer-packing-driven fluorescence in solid state arising from the three-dimensional arrangement of the pyrene units among layers. Layer stacking within these 2D-COF materials to give either eclipsed or staggered conformations can be controlled, at an atomic level through chemical design of the building blocks used in their synthesis. Theoretical calculations have been used to rationalize the different preferential packing between both COFs. IMDEA-COF-1shows green emission with absolute photoluminescence quantum yield of 3.5% in solid state. This material represents the first example of imine-linked 2D-COF showing emission in solid state.

A representative mesoporous metal–organic-framework (MOF) material, NU-1000, has been rendered electronically conductive via a robust inorganic approach that permits retention of MOF crystallinity and porosity. The approach is based on condensed-phase grafting of molecular tin species onto the MOF nodes via irreversible reaction with hydroxyl and aqua ligands presented at the node surface, a self-limiting process termed solvothermal installation(of metal ions) in MOFs (SIM, a solution-phase analog of atomic layer deposition in MOFs). Treatment of the modified MOF with aerated steam at 120 °C converts the grafted tin molecules to tetratin(IV)oxy clusters, with the clusters being sited between insulating pairs of zirconia-like nodes (the zirconium component being key to endowing the parent material with requisite chemical and thermal stability). By introducing new O–H presenting ligands on the modified-MOF node, the high-temperature steam step additionally serves to reset the material to reactive form, thus enabling a second self-limiting tin-grafting step to be run (and after further steam treatment, enabling a third). Difference-envelop-density (DED) analyses of synchrotron-derived X-ray scattering data, with and without installed tin species, show that the clusters formed after one cycle are spatially isolated, but that repetitive SIM cycling adds metal and oxygen ions in a way that enshrouds nodes, links clusters, and yields continuous one-dimensional strands of oxy-tin(IV), oriented exclusively along the caxis of the MOF. Two-probe conductivity measurements show that the parent MOF and the version containing isolated oxy-tin(IV) clusters are electrically insulating, but that the versions featuring continuous strands show an electrical conductivity of 1.8 × 10–7S/cm after three Sn-SIM cycles. When combined with interdigitated microelectrodes, the solvent-free and conductive-glass-modified material (three Sn-SIM cycles) displays a substantial and persistent increase in electrical conductivity during exposure to 5% H2, indicating a role for dissociated H2as an electronic dopant. The increase can be repetitively reversed by alternating H2with air, illustrating the ability of the conductive MOF to function as a resistive sensor for H2and suggesting further potential applications that may capitalize on the combination of high volumetric surface area, high mesoporosity, high chemical and thermal stability, and significant electrical conductivity.

Direct control over structure and location of catalytic species deposited on amorphous supports represents a formidable challenge in heterogeneous catalysis. In contrast, a structurally well-defined, crystalline metal–organic framework (MOF) can be rationally designed using postsynthetic techniques to allow for desired structural or locational changes of deposited metal ions. Herein, naphthalene dicarboxylate linkers are incorporated in the MOF, NU-1000, to block the small cavities where few-atom clusters of cobalt oxide preferentially grow, inducing catalyst deposition toward hitherto ill-favored grafting sites orientated toward NU-1000s mesoporous channels. Despite the different cobalt oxide location, the resulting material is still an active propane oxidative dehydrogenation catalyst at low temperature, reaching a turnover frequency of 0.68 ± 0.05 h–1at 230 °C and confirming the utility of MOFs as crystalline supports to guide rational design of catalysts.

Nanocasting can be a useful strategy to transfer the catalytic metal clusters in metal–organic frameworks (MOFs) to an all-inorganic support such as silica. The incorporation of silica in the MOF pores as a secondary support has the potential to extend the application of the highly tunable metal-based active sites in MOFs to high temperature catalysis. Here, we demonstrate the applicability of the nanocasting method to a range of MOFs that incorporate catalytically attractive hexazirconium, hexacerium, or pentanickel oxide-based clusters (UiO-66, (Ce)UiO-66, (Ce)UiO-67, (Ce)MOF-808, DUT-9, and In- and Ni-postmetalated NU-1000). We describe, in tutorial form, the challenges associated with nanocasting of MOFs that are related to their small pore size and to considerations of chemical and mechanical stability, and we provide approaches to overcome some of these challenges. Some of these nanocast materials feature the site-isolated clusters in a porous, thermally stable silica matrix, suitable for catalysis at high temperatures; in others, structural rearrangement of clusters or partial cluster aggregation occurs, but extensive aggregation can be mitigated by the silica skeleton introduced during nanocasting.

Here we describe the topological transformation of the pores of a new framework in the bio-MOF-100 family (dia-c) into the known isomer (lcs) by doubling the pore volume, which occurs during postsynthesis modifications. During this transformation, reassembling of the metal–organic framework (MOF) building blocks into a completely different framework occurs, involving breaking/forming of metal–ligand bonds. MOF crystallinity and local structure are retained, as determined by powder X-ray diffraction (PXRD) and pair distribution function (PDF) analyses, respectively. We exploited the inherent dynamism of bio-MOF-100 by coupling chemical decorations of the framework using solvent-assisted ligand exchange to the topological change. Following this method and starting from the pristine dense dia-cphase, open lcs-bio-MOF-100 was prepared and functionalized in situ with an iridium complex (IrL). Alternatively, the dia-cMOF could be modified with wide-ranging amounts of IrL up to ca. 50 mol %, as determined by solution 1H NMR spectroscopy, by tuning the concentration of the solutions used and with no evidence for isomer transformation. The single-site nature of the iridium complexes within the MOFs was assessed by X-ray absorption spectroscopy (XAS) and PDF analyses. Ligand exchanges occurred quantitatively at room temperature, with no need of excess of the iridium metallolinker.

Zr-based metal–organic frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Additionally, their crystalline nature affords the opportunity for molecular level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr6nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and atomic layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, respectively. The location of the deposited Co species in the two materials is determined via difference envelope density (DED) analysis. Upon activation in a flow of O2at 230 °C, both materials catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. Catalytic activity as well as propene selectivity of these two catalysts, however, is different under the same experimental conditions due to differences in the Co species generated in these two materials upon activation as observed by in situX-ray absorption spectroscopy. A potential reaction mechanism for the propane ODH process catalyzed by Co-SIM+NU-1000 is proposed, yielding a low activation energy barrier which is in accord with the observed catalytic activity at low temperature.

Photocatalytic H2generation is investigated over a series of Ga-modified ZnO photocatalysts that were prepared by hydrothermal methods. It is found that the structural, textural, and optoelectronic properties remarkably depend on the Ga content. The photocatalytic activity is higher in samples with Ga content equal to or lower than 5.4 wt %, which are constituted by Zn1–xGaxO phases. Structural, textural, and optoelectronic characterization, combined with theoretical calculations, reveals the effect of Ga in the doped ZnO structures. Higher Ga incorporation leads to the formation of an additional ZnGa2O4phase with spinel structure. The presence of such a phase is detrimental for the textural and optoelectronic properties of the photocatalysts, leading to a decrease in H2production. When Pt is used as the cocatalyst, there is an increase of 1 order of magnitude in the activity with respect to the bare photocatalysts. This is a result of Pt acting as an electron scavenger, decreasing the electron–hole recombination rate and boosting the H2evolution reaction.

Herein, we present a Ca‐based metal–organic framework named AEPF‐1, which is an active and selective catalyst in olefin hydrogenation reactions. AEPF‐1 exhibits a phase transition upon desorption of guest molecules. This structural transformation takes place by a crystal to crystal transformation accompanied by the loss of single‐crystal integrity. Powder diffraction methods and computational studies were applied to determine the structure of the guest‐free phase. This work also presents data on the exceptional adsorption behavior of this material, which is shown to be capable of separating polar from nonpolar organic solvents, and is a good candidate for selective solvent adsorption under mild conditions.

Covalent organic frameworks (COFs) are porous materials formed through condensation reactions of organic molecules viathe formation of dynamic covalent bonds. Among COFs, those based on imine and β-ketoenamine linkages offer an excellent platform for binding metallic species such as copper to design efficient heterogeneous catalysts. In this work, imine- and β-ketoenamine-based COF materials were modified with catalytic copper sites following a metallation method, which favored the formation of binding amine defects. The obtained copper-metallated COF materials were tested as heterogeneous catalysts for 1,3-dipolar cycloaddition reactions, resulting in high yields and recyclability.

Cheap thrills:A new metal–organic framework, based on cheap, abundant calcium, with the bent ligand, 4,4′‐hexafluoroisopropylidenebisbenzoic acid, serves as a highly efficient heterogeneous catalyst for the hydrogenation of styrene to form ethyl benzene under mild conditions. Complete hydrogenation occurs after 2 h at 373 K without formation of byproducts.

Review: 69 refs.

The cover picture showsthe olefin hydrogenation reaction inside the porous structure of AEPF‐1, a calcium‐based metal–organic framework (MOF). In their Communication on page 147 ff.,Gutiérrez‐Puebla et al. describe the preparation and studies of this material, which is a highly efficient heterogeneous catalyst for the hydrogenation of styrene to form ethylbenzene under mild conditions. The calcium‐based MOF is a comparatively cheap and green alternative to conventional precious metal‐based alkene hydrogenation catalysts.