Titanium(IV)‐based metal‐organic frameworks (Ti‐MOFs) have received significant attention in recent years due to their numerous photocatalytic applications. We herein prepare the single‐crystalline ...Ti‐carboxylate MOF (DGIST‐1) composed of an unprecedented Ti‐oxo chain cluster and the porphyrinic ligand, TCPP (tetrakis(4‐carboxyphenyl)porphyrin). Preformed Ti‐oxo clusters were used as Ti4+ sources to avoid the spontaneous hydrolysis and condensation reactions of traditional Ti‐alkoxide precursors, thus, enabling the formation of the highly crystalline Ti‐MOF. The successfully activated DGIST‐1 exhibited a higher surface area (i.e., 1957.3 m2 g−1) than previously reported Ti‐MOFs due to its high crystallinity. Furthermore, the visible‐light‐responsive photocatalytic activity of DGIST‐1 was confirmed by the simultaneous generation of singlet oxygen (1O2) and superoxide (.O2−) species, in addition to the highly efficient and selective oxidation of benzyl alcohol to benzaldehyde.
A single‐crystalline Ti‐porphyrinic MOF with an unprecedented Ti‐oxo chain cluster was newly synthesized. The visible‐light‐induced photocatalytic activity of this MOF was demonstrated by its application to the generation of reactive oxygen species and the selective benzyl alcohol oxidation to give benzaldehyde.
Cross‐responsive chemical sensors are in high demand owing to their ability to distinguish a broad range of analytes. In this study, a vapochromic sensor array based on metal–organic frameworks ...(MOFs), which exhibits distinct patterns when exposed to volatile organic compounds (VOCs) and humidity, is developed. Conventional sensor arrays consist of various receptors that produce different responses. The vapochromic MOF‐based sensor comprises dicopper paddlewheel clusters and dimethylamine azobenzene as binary colorimetric sensing moieties. Upon exposure to VOCs, the constructed sensor encompasses a broad spectrum of colors, ranging from green to red. Furthermore, the color of the MOF is influenced by the solvent used during the pretreatment. Consequently, monolayered MOF thin films can be adapted to multicomponent array systems by immersing the MOF in different solvents. This system provides both qualitative and quantitative sensing, generating unique color patterns corresponding to specific VOC types. Notably, the sensor successfully discriminates each of 14 common VOCs and water and accurately categorizes unknown samples. Moreover, the system undergoes reversible color changes in response to humidity, obviating the need for high‐temperature regeneration steps. This novel approach offers insights into the versatile applications of MOFs by creating a colorimetric sensor array capable of detecting various analytes.
A colorimetric metal–organic framework (MOF) sensor array is developed to detect volatile organic compounds (VOCs) and humidity. This MOF changes color from red to green in response to VOCs, influenced by solvent pretreatment. The system enables qualitative and quantitative VOC sensing. This research highlights the advanced potential of MOF‐based colorimetric sensors.
Flexible metal–organic frameworks (MOFs) are highly desirable in host–guest chemistry owing to their almost unlimited structural/functional diversities and stimuli‐responsive pore architectures. ...Herein, we designed a flexible Zr‐MOF system, namely PCN‐700 series, for the realization of switchable catalysis in cycloaddition reactions of CO2 with epoxides. Their breathing behaviors were studied by successive single‐crystal X‐ray diffraction analyses. The breathing amplitudes of the PCN‐700 series were modulated through pre‐functionalization of organic linkers and post‐synthetic linker installation. Experiments and molecular simulations confirm that the catalytic activities of the PCN‐700 series can be switched on and off upon reversible structural transformation, which is reminiscent of sophisticated biological systems such as allosteric enzymes.
An open and shut case: The inherent cavities and dynamic behavior of flexible MOFs, bear a close resemblance to regulatory enzymes. Switchable activation and deactivation of their catalytic properties occurs on pore opening and closing by solvation/solvent removal.
Creating ordered two-dimensional (2D) metal–organic framework (MOF) nanosheets has attracted extensive interest. However, it still remains a great challenge to synthesize ultrathin 2D MOF nanosheets ...with controlled thickness in high yields. In this work, we demonstrate a novel intercalation and chemical exfoliation approach to obtain MOF nanosheets from intrinsically layered MOF crystals. This approach involves two steps: first, layered porphyrinic MOF crystals are intercalated with 4,4′-dipyridyl disulfide through coordination bonding with the metal nodes; subsequently, selective cleavage of the disulfide bond induces exfoliation of the intercalated MOF crystals, leading to individual freestanding MOF nanosheets. This chemical exfoliation process can proceed efficiently at room temperature to produce ultrathin (∼1 nm) 2D MOF nanosheets in ∼57% overall yield. The obtained ultrathin nanosheets exhibit efficient and far superior heterogeneous photocatalysis performance compared with the corresponding bulk MOF.
An unprecedented correlation between the catalytic activity of a Zr‐based UiO‐type metal‐organic framework (MOF) and its degree of interpenetration (DOI) is reported. The DOI of an MOF is hard to ...control owing to the high‐energy penalty required to construct a partially interpenetrated structure. Surprisingly, strong interactions between building blocks (inter‐ligand hydrogen bonding) facilitate the formation of partially interpenetrated structures under carefully regulated synthesis conditions. Moreover, catalytic conversion rates for cyanosilylation and Knoevenagel condensation reactions are found to be proportional to the DOI of the MOF. Among MOFs with DOIs in the 0–100% range, that with a DOI of 87% is the most catalytically active. Framework interpenetration is known to lower catalytic performance by impeding reactant diffusion. A higher effective reactant concentration due to tight inclusion in the interpenetrated region is possibly responsible for this inverted result.
Preparing partially interpenetrated metal‐organic frameworks (MOFs) enables the relationship between MOF catalytic activity and degree of interpenetration to be understood. Substrate diffusion is no longer a catalytic kinetics determining factor when the interpenetrated MOF contains sufficiently large pores. High substrate affinity and the closely arranged catalytically active sites in the interpenetrated lattices cooperatively accelerate reactions.
Through a kinetically controlled synthetic process, we synthesized PCN-223, a new porphyrinic Zr-MOF constructed from the newly reported hexagonal prismatic 12-connected Zr6 cluster through an ...unusual disordered arrangement, giving rise to the first example of the shp-a network in MOFs. With its extremely high connectivity, PCN-223 shows high stability in aqueous solutions with a wide range of pH. Cationic PCN-223(Fe) formed by postsynthetic treatment is an excellent recyclable heterogeneous catalyst for the hetero-Diels–Alder reaction.
Cooperative cluster metalation and ligand migration were performed on a Zr‐MOF, leading to the isolation of unique bimetallic MOFs based on decanuclear Zr6M4 (M=Ni, Co) clusters. The M2+ reacts with ...the μ3‐OH and terminal H2O ligands on an 8‐connected Zr6O4(OH)8(H2O)4 cluster to form a bimetallic Zr6M4O8(OH)8(H2O)8 cluster. Along with the metalation of Zr6 cluster, ligand migration is observed in which a Zr–carboxylate bond dissociates to form a M–carboxylate bond. Single‐crystal to single‐crystal transformation is realized so that snapshots for cooperative cluster metalation and ligand migration processes are captured by successive single‐crystal X‐ray structures. In3+ was metalated into the same Zr‐MOF which showed excellent catalytic activity in the acetaldehyde cyclotrimerization reaction. This work not only provides a powerful tool to functionalize Zr‐MOFs with other metals, but also structurally elucidates the formation mechanism of the resulting heterometallic MOFs.
Mixed metal MOF: Cooperative cluster metalation and ligand migration were performed on a Zr‐MOF, leading to the isolation of Zr6M4 based bimetallic MOFs (right). This strategy allows for the functionalization of Zr‐MOFs with other metals for a variety of promising applications.
Stimuli‐responsive metal–organic polyhedra (srMOPs) functionalized with azobenzene showed UV‐irradiation‐induced isomerization from the insoluble trans‐srMOP to the soluble cis‐srMOP, whereas ...irradiation with blue light reversed this process. Guest molecules were trapped and released upon cis‐to‐trans and trans‐to‐cis isomerization of the srMOPs, respectively. This study provides a new direction in the ever‐diversifying field of MOPs, while laying the groundwork for a new class of optically responsive materials.
Lock in the guests, later set them free: Stimuli‐responsive metal–organic polyhedra (srMOPs) functionalized with azobenzene showed UV‐light‐induced isomerization from insoluble srMOPs substituted with trans‐azobenzene to soluble srMOPs with cis‐azobenzene units; irradiation with blue light reversed this process (see picture). Guest molecules were trapped upon cis‐to‐trans and released upon trans‐to‐cis isomerization of the azobenzene units.
A series of highly stable MOFs with 3-D nanochannels, namely PCN-224 (no metal, Ni, Co, Fe), have been assembled with six-connected Zr6 cluster and metalloporphyrins by a linker-elimination strategy. ...The PCN-224 series not only exhibits the highest BET surface area (2600m2/g) among all the reported porphyrinic MOFs but also remains intact in pH = 0 to pH = 11 aqueous solution. Remarkably, PCN-224(Co) exhibits high catalytic activity for the CO2/propylene oxide coupling reaction and can be used as a recoverable heterogeneous catalyst.
A reaction between a ZrIV salt and a porphyrinic tetracarboxylic acid leads to a metal–organic framework (MOF) with two types of open channels, representing a MOF featuring a (4,8)-connected sqc net. ...The MOF remains intact in both boiling water and aqueous solutions with pH ranging from 1 to 11, a remarkably extensive pH range that a MOF can sustain. Given its exceptional stability and pH-dependent fluorescent intensity, the MOF can potentially be applied in fluorescent pH sensing.
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