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Metal‐organic frameworks (MOFs) have attracted significant attention as porous catalyst platforms due to the synthetic modularity of these materials and the diversity of lattice‐confined catalytic active sites that are readily embedded within periodic crystalline frameworks. MOFs offer platforms to heterogenize molecular catalysts, stabilize novel coordination motifs, and leverage confinement effects in catalysis. Crystallinity allows diffraction‐based methods to be employed in the characterization of these catalysts. Access to crystalline MOFs typically requires reversible construction of the metal−ligand (M−L) bonds that connect the SBUs, which provides a mechanism to anneal defects during crystallization. While the required M−L bond reversibility is often promoted by synthesis at elevated temperature, access to crystalline materials based on either transition metals with characteristic slow exchange kinetics or highly basic donor ligands remains a synthetic challenge. Here, we highlight synthetic strategies that leverage M−L exchange kinetics to access MOFs based on kinetically inert ions and extensions of these strategies to the assembly of atomically precise multimetallic materials. [ABSTRACT FROM AUTHOR]

A photoactive porphyrinic metal−organic framework (MOF) has been prepared by exchanging Ti into a Zr‐based MOF precursor. The resultant mixed‐metal Ti/Zr porphyrinic MOF demonstrates much‐improved efficiency for gas‐phase CO2 photoreduction into CH4 and CO under visible‐light irradiation using water vapor compared to the parent Zr‐MOF. Insightful studies have been conducted to probe the photocatalysis processes. This work provides the first example of gas‐phase CO2 photoreduction into methane without organic sacrificial agents on a MOF platform, thereby paving an avenue for developing MOF‐based photocatalysts for application in CO2 photoreduction and other types of photoreactions. [ABSTRACT FROM AUTHOR]

Atomistic control of the coordination environment of lattice ions and the distribution of metal sites within crystalline mixed‐metal coordination polymers remain significant synthetic challenges. Herein is reported the mechanochemical synthesis of a reticular family of crystalline heterobimetallic metal–organic frameworks (MOFs) is now achieved by polymerization of molecular Ru2[II,III] complexes, featuring unprotected carboxylic acid substituents, with Cu(OAc)2. The resulting crystalline heterobimetallic MOFs are solid solutions of Ru2 and Cu2 sites housed within [M3L2] phases. The developed mechanochemical strategy is modular and allows for systematic control of the primary coordination sphere of the Ru2 sites within an isoreticular family of materials. This strategy is anticipated to provide a rational approach to atomically precise mixed‐metal materials. [ABSTRACT FROM AUTHOR]

The potential to exert atomistic control over the structure of site‐isolated catalyst sites, as well as the topology and chemical environment of interstitial pore spaces, has inspired efforts to apply porous metal‐organic frameworks (MOFs) as catalysts for fine chemical synthesis. In analogy to enzyme‐catalyzed reactions, MOF catalysts have been proposed as platforms in which substrate confinement could be used to achieve chemo‐ and stereoselectivities that are orthogonal to solution‐phase catalysts. In order to leverage the tunable pore topology of MOFs to impact catalyst selectivity, catalysis must proceed at interstitial catalyst sites, rather than at solvent‐exposed interfacial sites. This Minireview addresses challenges inherent to interstitial MOF catalysis by 1) describing the diffusional processes available to sorbates in porous materials, 2) discussing critical factors that impact the diffusion rate of substrates in porous materials, and 3) presenting in operando experimental strategies to assess the relative rates of substrate diffusion and catalyst turnover in MOF catalysis. It is anticipated that the continued development of in operando tools to evaluate substrate diffusion in porous catalysts will advance the application of these materials in fine chemical synthesis. Interfacial or interstitial catalysis? Metal‐organic frameworks (MOFs) have been advanced as catalysts for fine‐chemical synthesis. However, in order to access chemical selectivities that differ from homogenous catalysts, reactions must occur within the pore structure. This Minireview addresses the challenges associated with interstitial MOF catalysis. [ABSTRACT FROM AUTHOR]

Abstract: Herein, we report that a new flexible coordination network, NiL2 (L=4‐(4‐pyridyl)‐biphenyl‐4‐carboxylic acid), with diamondoid topology switches between non‐porous (closed) and several porous (open) phases at specific CO2 and CH4 pressures. These phases are manifested by multi‐step low‐pressure isotherms for CO2 or a single‐step high‐pressure isotherm for CH4. The potential methane working capacity of NiL2 approaches that of compressed natural gas but at much lower pressures. The guest‐induced phase transitions of NiL2 were studied by single‐crystal XRD, in situ variable pressure powder XRD, synchrotron powder XRD, pressure‐gradient differential scanning calorimetry (P‐DSC), and molecular modeling. The detailed structural information provides insight into the extreme flexibility of NiL2. Specifically, the extended linker ligand, L, undergoes ligand contortion and interactions between interpenetrated networks or sorbate–sorbent interactions enable the observed switching. [ABSTRACT FROM AUTHOR]

Abstract: Metal–organic frameworks (MOFs) have garnered substantial interest as platforms for site‐isolated catalysis. Efficient diffusion of small‐molecule substrates to interstitial lattice‐confined catalyst sites is critical to leveraging unique opportunities of these materials as catalysts. Understanding the rates of substrate diffusion in MOFs is challenging, and few in situ chemical tools are available to evaluate substrate diffusion during interstitial MOF chemistry. Herein, we demonstrate nitrogen atom transfer (NAT) from a lattice‐confined Ru2 nitride to toluene to generate benzylamine. We use the comparison of the intramolecular deuterium kinetic isotope effect (KIE), determined for amination of a partially deuterated substrate, with the intermolecular KIE, determined by competitive amination of a mixture of perdeuterated and undeuterated substrates, to establish the relative rates of substrate diffusion and interstitial chemistry. We anticipate that the developed KIE‐based experiments will contribute to the development of porous materials for group‐transfer catalysis. [ABSTRACT FROM AUTHOR]

A microporous Zn-based anionic metal-organic framework (MOF) was synthesized with triangular 4,4′,4′′-(pyridine-2,4,6-triyl)tribenzoic acid. The anionic MOF material featuring open channels proved to be a good capturing agent for the cationic dye methylene blue. In addition, the Zn-MOF demonstrated excellent catalytic activity for CO2 fixation by cycloaddition reaction with epoxides for the generation of cyclic carbonates. [ABSTRACT FROM AUTHOR]

Described for the first time is that carbon dioxide (CO2) can be successfully inserted into aryl C−H bonds of the backbone of a metal-organic framework (MOF) to generate free carboxylate groups, which serve as Brønsted acid sites for efficiently catalyzing the methanolysis of epoxides. The work delineates the very first example of utilizing CO2 for heterogeneous C−H activation and carboxylation reactions on MOFs, and opens a new avenue for CO2 chemical transformations under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Inspiration for molecular design and construction can be derived from mathematically based structures. In the quest for new materials, the adaptation of new building blocks can lead to unexpected results. Towards these ends, the quantitative single-step self-assembly of a shape-persistent, Archimedean-based building block, which generates the largest molecular sphere (a cuboctahedron) that has been unequivocally characterized by synchrotron X-ray analysis, is described. The unique properties of this new construct give rise to a dilution-based transformation into two identical spheres (octahedra) each possessing one half of the molecular weight of the parent structure; concentration of this octahedron reconstitutes the original cuboctahedron. These chemical phenomena are reminiscent of biological fission and fusion processes. The large 6 nm cage structure was further analyzed by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross-section analysis. New routes to molecular encapsulation can be envisioned. [ABSTRACT FROM AUTHOR]

Inspiration for molecular design and construction can be derived from mathematically based structures. In the quest for new materials, the adaptation of new building blocks can lead to unexpected results. Towards these ends, the quantitative single-step self-assembly of a shape-persistent, Archimedean-based building block, which generates the largest molecular sphere (a cuboctahedron) that has been unequivocally characterized by synchrotron X-ray analysis, is described. The unique properties of this new construct give rise to a dilution-based transformation into two identical spheres (octahedra) each possessing one half of the molecular weight of the parent structure; concentration of this octahedron reconstitutes the original cuboctahedron. These chemical phenomena are reminiscent of biological fission and fusion processes. The large 6 nm cage structure was further analyzed by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross-section analysis. New routes to molecular encapsulation can be envisioned. [ABSTRACT FROM AUTHOR]

Crystal engineering of the nbo metal-organic framework (MOF) platform MOF-505 with a custom-designed azamacrocycle ligand (1,4,7,10-tetrazazcyclododecane- N, N′, N′′, N′′′-tetra- p-methylbenzoic acid) leads to a high density of well-oriented Lewis active sites within the cuboctahedral cage in MMCF-2, [Cu2(Cu-tactmb)(H2O)3(NO3)2]. This MOF demonstrates high catalytic activity for the chemical fixation of CO2 into cyclic carbonates at room temperature under 1 atm pressure. [ABSTRACT FROM AUTHOR]

The design and synthesis of polyhedra using coordination‐driven self‐assembly has been an intriguing research area for synthetic chemists. Metal‐organic polyhedra are a class of intricate molecular architectures that have garnered significant attention in the literature due to their diverse structures and potential applications. Hereby, we report Cu‐MOP, a bifunctional metal‐organic cuboctahedra built using 2,6‐dimethylpyridine‐3,5‐dicarboxylic acid and copper acetate at room temperature. The presence of both Lewis basic pyridine groups and Lewis acidic copper sites imparts catalytic activity to Cu‐MOP for the tandem one‐pot deacetalization‐Knoevenagel/Henry reactions. The effect of solvent system and time duration on the yields of the reactions was studied, and the results illustrate the promising potential of these metal‐organic cuboctahedra, also known as nanoballs for applications in catalysis. [ABSTRACT FROM AUTHOR]

Review: 112 refs. [ABSTRACT FROM AUTHOR]

The CoII atom in bis(5-aminotetrazole-1-acetato)tetraaquacobalt(II), [Co(C3H4N5O2)2(H2O)4], (I), is octahedrally coordinated by six O atoms from two 5-aminotetrazole-1-acetate (atza) ligands and four water molecules. The molecule has a crystallographic centre of symmetry located at the CoII atom. The molecules of (I) are interlinked by hydrogen-bond interactions, forming a two-dimensional supramolecular network structure in the ac plane. The CdII atom in catena-poly[[cadmium(II)]-bis(μ-5-aminotetrazole-1-acetato], [Cd(C3H4N5O2)2] n, (II), lies on a twofold axis and is coordinated by two N atoms and four O atoms from four atza ligands to form a distorted octahedral coordination environment. The CdII centres are connected through tridentate atza bridging ligands to form a two-dimensional layered structure extending along the ab plane, which is further linked into a three-dimensional structure through hydrogen-bond interactions. [ABSTRACT FROM AUTHOR]