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This work introduces a robust acid‐base catalytic system based on the zirconium‐based metal‐organic framework (Zr‐MOF) MOF‐808, selected for its open structure, high stability, and low presence of structural defects compared to other Zr‐MOFs. Four bifunctional benzoate ligands bearing free carboxylic acid (‐COOH) and nitrogen‐containing groups were introduced into the MOF‐808 using solvent‐assisted ligand exchange methods. Unlike other materials, the acid and base sites in the bifunctional MOF‐808 materials are situated in the same capping ligand, leading to a bifunctional behavior between the two neighboring sites. The system was tested for Knoevenagel condensation and deacetylation‐Knoevenagel tandem reactions, demonstrating high catalytic activity and excellent yields. Additionally, computational modeling provided insights into the catalytic mechanism and the role of the acid‐base sites. The study provides a better understanding of the unique behavior of the bifunctional MOF‐808 catalyst and offers prospects for designing new and efficient catalytic systems for organocatalysis. [ABSTRACT FROM AUTHOR]

Encapsulating ultrasmall Cu nanoparticles inside Zr‐MOFs to form core–shell architecture is very challenging but of interest for CO2 reduction. We report for the first time the incorporation of ultrasmall Cu NCs into a series of benchmark Zr‐MOFs, without Cu NCs aggregation, via a scalable room temperature fabrication approach. The Cu NCs@MOFs core–shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs, regardless of their very similar intrinsic properties at the atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the CuI sites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze CO2 photoreduction. This synergetic effect may pave the way for the design of low‐cost and efficient catalysts for CO2 photoreduction into high‐value chemical feedstock. [ABSTRACT FROM AUTHOR]

Encapsulating ultrasmall Cu nanoparticles inside Zr‐MOFs to form core–shell architecture is very challenging but of interest for CO2 reduction. We report for the first time the incorporation of ultrasmall Cu NCs into a series of benchmark Zr‐MOFs, without Cu NCs aggregation, via a scalable room temperature fabrication approach. The Cu NCs@MOFs core–shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs, regardless of their very similar intrinsic properties at the atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the CuI sites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze CO2 photoreduction. This synergetic effect may pave the way for the design of low‐cost and efficient catalysts for CO2 photoreduction into high‐value chemical feedstock. [ABSTRACT FROM AUTHOR]

The doping of zirconium based EHU-30 and EHU-30-NH2 metal–organic frameworks with copper(II) yielded a homogeneous distribution of the dopant with a copper/zirconium ratio of 0.04–0.05. The doping mechanism is analysed by chemical analysis, microstructural analysis and pair distribution function (PDF) analysis of synchrotron total scattering data in order to get deeper insight into the local structure. According to these data, the Cu(II) atoms are assembled within the secondary building unit by a transmetalation reaction, contrarily to UiO-66 series in which the post-synthetic metalation of the MOF takes place through chemical anchorage. The resulting materials doubled the overall performance of the parent compounds for the CO2 electroreduction, while retained stable the performance during continuous transformation reaction. [ABSTRACT FROM AUTHOR]

Stabilizing catalytic iron-oxo-clusters within nanoporous metal–organic frameworks (MOFs) is a powerful strategy to prepare new active materials for the degradation of toxic chemicals, such as bisphenol A. Herein, we combine pair distribution function analysis of total X-ray scattering data and X-ray absorption spectroscopy, with computational modelling to understand the local structural nature of added redox-active iron-oxo clusters bridging neighbouring zirconia-nodes within MOF-808. [ABSTRACT FROM AUTHOR]

Layered covalent organic frameworks (2D‐COFs), composed of reversible imine linkages and accessible pores, offer versatility for chemical modifications towards the development of catalytic materials. Nitrogen‐enriched COFs are good candidates for binding Pd species. Understanding the local structure of reacting Pd sites bonded to the COF pores is key to rationalize interactions between active sites and porous surfaces. By combining advanced synchrotron characterization methods with periodic computational DFT modeling, the precise atomic structure of catalytic Pd sites attached to local defects is resolved within an archetypical imine‐linked 2D‐COF. This material was synthesized using an in situ method as a gel, under which imine hydrolysis and metalation reactions are coupled. Local defects formed in situ within imine‐linked 2D‐COF materials are highly reactive towards Pd metalation, resulting in active materials for Suzuki–Miyaura cross‐coupling reactions. [ABSTRACT FROM AUTHOR]

A two-dimensional imine-linked covalent organic framework bearing pyrene has been prepared and exfoliated in water as nanosheets to produce a stable water colloid. As a proof-of-concept, this COF colloid has been used to detect the presence of several organic dyes and polynitro-aromatic derivatives. These results show the high potential of these nanomaterials for applications in chemical sensing of pollutants directly in water. [ABSTRACT FROM AUTHOR]

The polyoxometalate (POM), H3PW12O40, was postsynthetically incorporated into the metal–organic framework (MOF), NU-1000. The POM@MOF composite, PW12@NU-1000, was activated under mild conditions, resulting in a material whose diffraction pattern and spectroscopic properties differ from the same material heated at elevated temperatures. These discrepancies, corroborated by difference envelope density analyses, were attributed to the POM residing either in the mesoporous or microporous channels of NU-1000. As a testament to the importance of catalyst accessibility, the POM's locational change also induced a change in the composite's rate and selectivity toward oxidizing 2-chloroethyl ethyl sulfide. [ABSTRACT FROM AUTHOR]

Abstract: NU‐1000 is a robust and highly porous Zr‐based metal–organic framework (Zr‐MOFs) that has been proven to be an excellent catalyst support because of its well‐defined crystal structure, protonic grafting sites on its nodes, and thermal stability, all of which advantageously offer the possibility to study the nature of the catalytic reactive sites. Herein, we present a vanadium‐oxide catalyst supported on NU‐1000 synthesized by solvothermal deposition in MOFs (SIM), namely, V‐NU‐1000. The catalytic activity of V‐NU‐1000 was investigated by studying the oxidation of 4‐methoxybenzyl alcohol under an O2 atmosphere; this catalyst showed higher conversion and higher selectivity than vanadium‐oxide supported on high‐surface‐area zirconia (V‐ZrO2). The stability of V‐NU‐1000 was confirmed by recyclability and leaching tests, in which recycled V‐NU‐1000 had catalytic ability comparable to that of the fresh catalyst, and no loss in the metal loading was found in recollected V‐NU‐1000. [ABSTRACT FROM AUTHOR]

Abstract: Single atoms and few‐atom clusters of platinum are uniformly installed on the zirconia nodes of a metal‐organic framework (MOF) NU‐1000 via targeted vapor‐phase synthesis. The catalytic Pt clusters, site‐isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few‐atom clusters that depend upon synthesis conditions. Operando X‐ray absorption spectroscopy and X‐ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size‐selected clusters, including noble metals, on a high surface area support. [ABSTRACT FROM AUTHOR]

We explore the dynamic structure and reactivity of Cu species supported on NU-1000. By combining pair distribution function (PDF) analysis and difference envelope density (DED) analysis of in situ synchrotron-based X-ray scattering data, we simultaneously probe the local structure of supported Cu-species, their distribution within NU-1000 and distortions of the NU-1000 lattice under conditions relevant to catalysis and catalyst activation. These analyses show that atomic layer deposition (ALD) of Cu in NU-1000 (Cu-AIM) leads to the formation of Cu-oxo clusters within the small pores that connect the triangular and hexagonal channels. Exposure of Cu-AIM to a reducing atmosphere at 200 °C produces metallic Cu0 of two distinct particle sizes: ∼4 nm nanoparticles and small sub-nanometer clusters. The size of these nanoparticles appears to be constrained by NU-1000 pore dimensions, with evidence of the sub-nanometer clusters being bound within the triangular channels flanked by pyrene rings. This supported Cu0–NU-1000 system is catalytically active for gas-phase ethylene hydrogenation. Exposure of the catalyst to oxidative atmosphere re-oxidises the Cu species to a Cu2O cuprite phase. The dynamic restructuring of the system in different chemical environments underscores the importance of probing these systems in situ. [ABSTRACT FROM AUTHOR]

Remarkably simple IrIII catalysts enable the isomerization of primary and sec-allylic alcohols under very mild reaction conditions. X-ray absorption spectroscopy (XAS) and mass spectrometry (MS) studies indicate that the catalysts, with the general formula [Cp*IrIII], require a halide ligand for catalytic activity, but no additives or additional ligands are needed. [ABSTRACT FROM AUTHOR]

In situ pair distribution function (PDF) analyses and density functional theory (DFT) computations are used to probe local structural transitions of M6O8 nodes found in two metal organic frameworks (MOFs), NU-1000 and UiO-66, for M = Zr, Hf. Such transitions are found to occur without change to the global framework symmetry at temperatures within a range relevant to many potential MOF applications. For the particular M6(O)8 nodes studied here, the observed distortions can be mapped to polymorphic forms known for bulk ZrO2. In the MOF framework, however, node distortions are found to occur at substantially lower temperature than analogous distortions in bulk ZrO2 owing to the nanoscale nature of the former. [ABSTRACT FROM AUTHOR]

A series of iridium-functionalised UiO-67 metal–organic frameworks (MOFs) were synthesised under conditions that simulate kinetically- and thermodynamically-controlled regimes. The degree of functionalisation depends on the reaction time and relative acidity of the native- and metallo-linkers, and can be optimised by controlling the reaction time. [ABSTRACT FROM AUTHOR]

The chemical stability of metal-organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki-Miyaura cross-coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL-101-NH2(Cr). Four bases were compared for the reaction: K2CO3, KF, Cs2CO3 and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N2 sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL-101-NH2(Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases. [ABSTRACT FROM AUTHOR]

The synthesis of a metal-organic framework (UiO-67) functionalised simultaneously with two different transition metal complexes (Ir and Pd or Rh) through a one-pot procedure is reported for the first time. This has been achieved by an iterative modification of the synthesis parameters combined with characterisation of the resulting materials using different techniques, including X-ray absorption spectroscopy (XAS). The method also allows the first synthesis of UiO-67 with a very wide range of loadings (from 4 to 43 mol %) of an iridium complex ([IrCp*(bpydc)(Cl)Cl]2−; bpydc=2,2′-bipyridine-5,5′-dicarboxylate, Cp*=pentamethylcyclopentadienyl) through a pre-functionalisation methodology. [ABSTRACT FROM AUTHOR]

Four linear connecting amino acid derived ligands, 1-4, and one potentially three connecting, 5, were prepared by the reaction of the appropriate terephthaloyl dichloride or benzene-1,3,5-tricarbonyl trichloride with the methyl ester protected amino acid. Amino acids used here were alanine (1, 5), isoleucine (2), leucine (3) and valine (4). Crystalline forms of four amino acid substituted terephthalamides (2,2'-(terephthaloylbis(azanediyl))dipropanoic acid dihydrate 1;2,2'-(terephthaloylbis(azanediyl))bis(3-methylpentanoic acid) monohydrate 2;2,2'-(terephthaloylbis(azanediyl))bis(4-methylpentanoic acid) dihydrate 3;2,2'-(terephthaloylbis(azanediyl))bis(3-methylbutanoic acid) dihydrate 4) and one benzene-1,3,5-tricarboxamide molecule (2,2',2"-((benzene-1,3,5-tricarbonyl)tris(azanediyl))tripropionic acid hemihydrate 5) were characterised and the single crystal structures were solved. All the compounds form hydrogen bonded 2D and 3D nets. Linear connecting amino acid derivatives can be categorised into three groups depending on the hydrogen bond patterns and final structures. Compounds 1 and 2 form 3D structures but the final structure is different due to the different hydrogen bond synthons. Compounds 3 and 4 are isostructural and form 2D hydrogenbondedstructureswhile 5 forms a hydrogen bonded pcu-net. Intermolecular interactions have been analysed with Hirshfeld surfaces and graph set symbols. [ABSTRACT FROM AUTHOR]

We propose a multidisciplinary approach to face the interpretation of heterogeneous catalysis with alkaline-earth metal-organic frameworks (MOFs). Their oxygen-based polyhedra, which do not exhibit regular geometries, do act as very active Lewis acid sites. Four novel alkaline-earth MOFs that belong to three different structural types-Mg-AEPF-11, Mg-APF-12, Ca-AEPF-13 and Sr-APF-13-are reported, together with their net topologies, and a study of the symmetry distortions around the alkaline-earth metal polyhedra by using a continuous shape mapping (CShM) description. These MOFs are good catalysts in the selective hydrogenation of styrene. Even more, Sr-AEPF-13 shows the best conversions ever published with alkaline-earth MOFs for the hydrogenation of activated alkenes under mild conditions. A combination of crystallographic and topological analysis and theoretical calculations, together with experimental catalytic results, has been applied to understand the catalytic activity of these four novel alkaline-earth MOFs. This work demonstrates that the presence of symmetry-distorted alkaline-earth polyhedra gives rise to highly catalytic-active MOFs in the hydrogenation of activated alkenes. [ABSTRACT FROM AUTHOR]