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1,3,5-benzenetricarboxylate, biphenyl-3,4′,5-tricarboxylate,and [1,1′:3′,1″-terphenyl]-4,4″,5′-tricarboxylatereact with Cd(II) cations in the presence of meso-tetra(N-methyl-4-pyridyl) porphine cations to afford three metalloporphyrin-encapsulatingmetal–organic materials, porph@MOM-11, -12and -13, respectively. The metalloporphyrin moietiesare ordered within channels and closely fit hexagonal or rectangularcavities, thereby facilitating a better understanding of the structure-directingeffect that can be promoted by metalloporphyrins. Porph@MOM-12is noteworthy because it exhibits two distinct types of hexagonalchannels and it represents the first example of a net that exhibits mzztopology. [ABSTRACT FROM AUTHOR]

Removal of carbon dioxide (CO 2 ) from a CO 2 /N 2 mixture by utilizing CO 2 -selective sorbents is important from the perspective of energy security and environmental sustainability. Herein, a microporous metal-organic framework (MOF) composed of manganese(II) and a bifunctional linker 5-(4 H -1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid (H 2 L), [Mn(HL) 2 ] ( 1 ) is designed and synthesized using a hydrothermal method. Characterized by single-crystal X-ray diffraction (SCXRD), a microporous channel was found in the structure of compound 1 along the a -axis. Attributed to hydrogen-binding interactions between CO 2 molecules and N- and O-donor ligands in its microporous one-dimensional (1D) channel, compound 1 exhibits favorable adsorption of CO 2 over N 2 . Further, verified by experimental breakthrough tests, the CO 2 /N 2 mixture can be separated efficiently. This work provides potential guidance for designing CO 2 -selective MOFs for CO 2 /N 2 separation.

One-step adsorptive purification of ethylene (C 2 H 4 ) from a ternary mixture of acetylene (C 2 H 2 ), C 2 H 4 , and ethane (C 2 H 6 ) by a single material is of great importance but challenging in the petrochemical industry. Herein, a chemically robust olefin-linked covalent organic framework (COF), NKCOF-62, is designed and synthesized by a melt polymerization method employing tetramethylpyrazine and terephthalaldehyde as cheap monomers. This method avoids most of the disadvantages of classical solvothermal methods, which enable the cost-effective kilogram fabrication of olefin-linked COFs in one pot. Furthermore, NKCOF-62 shows remarkably selective adsorption of C 2 H 2 and C 2 H 6 over C 2 H 4 thanks to its unique pore environments and suitable pore size. Breakthrough experiments demonstrate that polymer-grade C 2 H 4 can be directly obtained from C 2 H 2 /C 2 H 6 /C 2 H 4 (1/1/1) ternary mixtures through a single separation process. Notably, NKCOF-62 is the first demonstration of the potential to use COFs for C 2 H 2 /C 2 H 6 /C 2 H 4 separation, which provides a blueprint for the design and construction of robust COFs for industrial gas separations.

Developing strategies to enhance the structural robustness of covalent organic frameworks (COFs) is of great importance. Here, we rationally design and synthesize a class of cross-linked COFs ( C COFs), in which the two-dimensional (2D) COF layers are anchored and connected by polyethylene glycol (PEG) or alkyl chains through covalent bonds. The bottom-up fabrication of these C COFs is achieved by the condensation of cross-linked aldehyde monomers and tritopic amino monomers. All the synthesized C COFs possess high crystallinity and porosity, and enhanced structural robustness surpassing the typical 2D COFs, which means that they cannot be exfoliated under ultrasonication and grinding due to the cross-linking effect. Furthermore, the cross-linked patterns of PEG units are uncovered by experimental results and Monte Carlo molecular dynamics simulations. It is found that all C COFs are dominated by vertical cross-layer (interlayer) connections (clearly observed in high-resolution transmission electron microscopy images), allowing them to form quasi-three-dimensional (quasi-3D) structures. This work bridges the gap between 2D COFs and 3D COFs and provides an efficient way to improve the interlayered stability of COFs.

Stimuli-responsive smart materials that can undergo reversible chemical/physical changes under external stimuli such as mechanical stress, heat, light, gas, electricity, and pH, are currently attracting increasing attention in the fields of sensors, actuators, optoelectronic devices, information storage, medical applications, and so forth. The current smart materials mostly concentrate on polymers, carbon materials, crystalline liquids, and hydrogels, which have no or low structural order (i.e., the responsive groups/moieties are disorderly in the structures), inevitably introducing deficiencies such as a relatively low response speeds, energy transformation inefficiencies, and unclear structure-property relationships. Consequently, crystalline materials with well-defined and regular molecular arrays can offer a new opportunity to create novel smart materials with improved stimuli-responsive performance. Crystalline materials include framework materials (e.g., metal-organic frameworks, MOFs; covalent organic frameworks, COFs) and molecular crystals (e.g., organic molecules and molecular cages), which have obvious advantages as smart materials compared to amorphous materials. For example, responsive groups/moieties can be uniformly installed in the skeleton of the crystal materials to form ordered molecular arrays, making energy transfer between external-stimulus signals and responsive sites much faster and more efficiently. Besides that, the well-defined structures facilitate in situ characterization of their structural transformation at the molecular level by means of various techniques and high-tech equipment such as in situ spectra and single-crystal/powder X-ray diffraction, thus benefiting the investigation and understanding of the mechanism behind the stimuli-responsive behaviors and structure-property relationships. Nevertheless, some unsolved challenges remain for crystalline smart materials (CSMs), hampering the fabrication of smart material systems for practical applications. For instance, as the materials' crystallinity increases, their processability and mechanical properties usually decrease, unavoidably hindering their practical application. Moreover, crystalline smart materials mostly exist as micro/nanosized powders, which are difficult to make stimuli-responsive on the macroscale. Thus, developing strategies that can balance the materials' crystallinity and processability and establishing macroscale smart material systems are of great significance for practical applications.In this Account, we mainly summarize the recent research progress achieved by our groups, including (i) the rational design and fabrication of new stimuli-responsive crystalline smart materials, including molecular crystals and framework materials, and an in-depth investigation of their response mechanism and structure-property relationship and (ii) creating chemical/physical modification strategies to improve the processability and mechanical properties for crystalline materials and establishing macroscale smart systems for practical applications. Overall, this Account summarizes the state-of-the-art progress of stimuli-responsive crystalline smart materials and points out the existing challenges and future development directions in the field.

The method of tumor microenvironment (TME)-responsive aggregation has become a promising approach to enhance treatment effect by improving the accumulation of nanoparticles in tumors. The enzymatic cross-linking strategy has widely attracted attention owing to its good aggregation stability and biocompatibility. However, the enzymes in nontumor tissue can also catalyze the cross-linking reaction and reduce accumulation of nanoparticles in tumor. In this work, a "dual key"-responsive strategy is utilized to construct a transglutaminase (TGase)/pH-responsive radiosensitizer (Au@TAcoGal) with specific aggregation behavior in hepatic tumor cells. Au@TAcoGal can retain its stability in blood circulation (pH 7.4) even in the presence of TGase in plasma. On reaching tumor sites, it can be endocytosed by hepatoma cells by the active targeting of phenylboronic acid (PBA) and aggregated under acidity and overexpression of TGase in cells. Due to its specific accumulation in hepatoma cells, radiotherapy can be operated under a lower dose of X-ray. The results show that the cellular accumulation of Au@TAcoGal increases by 30-70%, and the cell survival rate is less than 25% under X-ray irradiation. The antineoplastic results show that Au@TAcoGal exhibits a higher therapeutic effect, and the tumor inhibition rate can reach 84.21%.

The development of new techniques and materials that can separate ethylene from ethane is highly relevant in modern applications. Although adsorption-based separation techniques using metal-organic frameworks (MOFs) have gained increasing attention, the relatively low stability (especially water resistance) and unscalable synthesis of MOFs severely limit their application in real industrial scenarios. Addressing these challenges, we rationally designed and synthesized two new C 2 H 6 -selective MOF adsorbents ( NKMOF-8-Br and -Me ) with ultrahigh chemical and thermal stability, including water resistance. Attributed to the nonpolar/hydrophobic pore environments and appropriate pore apertures, the MOFs can capture C2 hydrocarbon gases at ambient conditions even in high humidity. The single-crystal structures of gas@NKMOF-8 realized the direct visualization of adsorption sites of the gases. Both the single-crystal data and simulated data elucidate the mechanism of selective adsorption. Moreover, the NKMOF-8 possesses high C 2 H 6 adsorption capacity and high selectivity, allowing for efficient C 2 H 6 /C 2 H 4 separation, as verified by experimental breakthrough tests. Most importantly, NKMOF-8-Br and -Me can be scalably synthesized through stirring at room temperature in minutes, which confers them with great potential for industrial application. This work offers new adsorbents that can address major chemical industrial challenges and provides an in-depth understanding of the gas binding sites in a visual manner.

It is of profound significance with regard to the global energy crisis to develop new techniques and materials that can convert the chemical potential of water into other forms of energy, especially electricity. To address this challenge, we built a new type of energy transduction pathway (humidity gradients → mechanical work → electrical power) using moisture-responsive crystalline materials as the media for energy transduction. Single-crystal data revealed that a flexible zeolitic pyrimidine framework material, ZPF-2-Co , could undergo a reversible structural transformation (β to α phase) with a large unit cell change upon moisture stimulus. Dynamic water vapor sorption analysis showed a gate-opening effect with a steep uptake at as low as 10% relative humidity (RH). The scalable green synthesis approach and the fast water vapor adsorption-desorption kinetics made ZPF-2-Co an excellent sorbent to harvest water from arid air, as verified by real water-harvesting experiments. Furthermore, we created a gradient distribution strategy to fabricate polymer-hybridized mechanical actuators based on ZPF-2-Co that could perform reversible bending deformation upon a variation of the humidity gradient. This mechanical actuator showed remarkable durability and reusability. Finally, coupling the moisture-responsive actuator with a piezoelectric transducer further converted the mechanical work into electrical power. This work offers a new type of moisture-responsive smart material for energy transduction and provides an in-depth understanding of the responsive mechanism at the molecular level.

A high filler content is often needed in polymer composite-based thermoelectric (TE) films to improve their performance. Nevertheless, this often leads to poor processability and poor mechanical performance. Herein, a biomimetic approach is adopted to facilitate the filler content up to 90.5 wt % in free-standing and flexible n-type PVDF/Ag 2 Se TE films, where PVDF dendricolloids are a solution mixed with Ag 2 Se nanowires (NWs), followed by filtration. These soft dendric nanoparticles within PVDF dendricolloids have high adhesivity and strong network-building ability, which allows the formation of "grapevine-grape"-like networks with soft dendritic particles and inorganic TE fillers as "grapevine" and "manicure finger grapes", respectively. The maximum power factor of 189.02 μW m -1 K -2 is achieved for a PVDF/Ag 2 Se mass ratio of 1:9.5 at 300 K. Meanwhile, excellent flexibility with only 15.8% decrease in electrical conductivity after 1000 bending cycles was observed. These properties at such a high filler content are attributed to the long-range grapevine-like network of soft PVDF dendritic particles and entanglement between numerous Ag 2 Se NWs. This work carves a path to fabricate high-performance free-standing flexible n-type TE composite films as well as other functional polymer composites requiring high inorganic filler loading.

Enzyme immobilization has been demonstrated to be a favorable protocol to promote industrialization of biomacromolecules. Despite tremendous efforts to develop new strategies and materials to realize this process, maintaining enzyme activity is still a formidable challenge. Herein we created a sacrificial templating method, using metal-organic frameworks (MOFs) as sacrificial templates to construct hollow covalent organic framework (COF) capsules for enzyme encapsulation. This strategy can provide a capacious microenvironment to unleash enzyme molecules. The improved conformational freedom of enzymes, enhanced mass transfer, and protective effect against the external environment ultimately boosted the enzymatic activities. We also found that this strategy possesses high versatility that is suitable for diverse biomacromolecules, MOF templates, and COF capsules. Moreover, the dimensions, pore sizes, and shell thickness of COF capsules can be conveniently tuned, allowing for customizing bioreactors for specific functions. For example, coencapsulation of different enzymes with synergistic functions were successfully demonstrated using this bioreactor platform. This study not only opens up a new avenue to overcome the present limitations of enzymatic immobilization in porous matrixes but also provides new opportunities for construction of biomicrodevices or artificial organelles based on crystalline porous materials.

Noble gases, especially krypton (Kr) and xenon (Xe), are widely applied in diverse fields. Developing new techniques and adsorbents to separate and purify Kr and Xe is in high demand. Herein, we reported a bimetallic metal-organic framework (MOF) (NKMOF-1-Ni) which possesses a narrow pore size (5.36 Å) and ultrahigh stability (e.g., stable in water for 1.5 years). Gas sorption measurements revealed that this MOF possessed much higher uptake for Xe than for Kr, Ar, or N 2 at room temperature in all pressure ranges. The calculation of adsorption isosteric heat and Grand Canonical Monte Carlo simulation verified that NKMOF-1-Ni had a stronger interaction with Xe than other tested gases. The results of ideal adsorbed solution theory selectivity and simulated breakthrough further showed that NKMOF-1-Ni had an outstanding separation performance of Xe/Kr, Xe/Ar, and Xe/N 2 . This study provides important guidance for future research to synthesize ideal sorbents to separate noble gases.

Carbonic anhydrase (CA) mimicking is an effective and environmentally friendly strategy for carbon dioxide sequestration. Herein, we developed a nonanuclear CA-mimetic zinc coordination complex ( 1 ) which possesses a coordination environment similar to that of CA's catalytically active zinc sites. Complex 1 exhibited excellent reusability, solvent and thermal stability, and gram-scale synthesis, which are essential for practical applications. It was found that complex 1 exhibited outstanding catalytic performance that is much better in comparison to that of the popular CA-mimetic compound Zn-cyclen and comparable to that of the reported metal-organic frameworks (e.g., CFA-1 ). Moreover, we found that its catalytic activity can be significantly improved via OAc - /OH - exchange and particle size reduction treatment. This study provides important guidance for the design of highly efficient CA-mimetic materials.

Fabrication of hybrid membranes composed of porous materials embedded in polymer matrices is a subject of topical interest. Herein, we introduce a new class of hybrid membranes: hyper-cross-linked metal-organic polyhedra (HCMOPs). These membranes are based upon soluble MOPs that can serve as high-connectivity nodes in hyper-cross-linked polymer networks. HCMOPs spontaneously form macro-scale, defect-free, freestanding membranes, and, thanks to the covalent cross-linking of MOPs, the resulting membranes possess multiple functionalities: strong water permeability; self-healing ability; antimicrobial activity; and better separation and mechanical performance than pristine polyimine membranes. This study introduces a new concept for the design and fabrication of multifunctional membranes and also broadens the applications of MOPs.

Inspired by the structure of carbonic anhydrase, we developed a robust ultramicroporous lanthanide metal-organic framework (MOF) platform (NKMOF-3-Ln), which possesses a porous pocket to selectively bind with CO 2 at ambient conditions. Notably, CO 2 molecules can be precisely observed in the single-crystal structure of NKMOF-3-Ln. Highly ordered CO 2 molecules can strongly interact with the framework via electrostatic interaction of nitrates. We found that the CO 2 adsorption capacity and binding energy were gradually enhanced as lanthanide contraction. The strong CO 2 binding affinity endows NKMOF-3-Ln with excellent CO 2 separation performance, which is verified by experimental breakthrough results. Moreover, because of the specific binding affinity of CO 2 , NKMOF-3-Eu showed a fluorescence response to CO 2 .

Carbonic anhydrase (CA) is a zinc-containing metalloprotein, in which the Zn active center plays the key role to transform CO 2 into carbonate. Inspired by nature, herein we used metal-organic frameworks (MOFs) to mimic CA for CO 2 conversion, on the basis of the structural similarity between the Zn coordination in MOFs and CA active center. The biomimetic activity of MOFs was investigated by detecting the hydrolysis of para-nitrophenyl acetate, which is a model reaction used to evaluate CA activity. The biomimetic materials (e.g., CFA-1) showed good catalytic activity, and excellent reusability, and solvent and thermal stability, which is very important for practical applications. In addition, ZIF-100 and CFA-1 were used to mimic CA to convert CO 2 gas, and exhibited good efficiency on CO 2 conversion compared with those of other porous materials (e.g., MCM-41, active carbon). This biomimetic study revealed a novel CO 2 treatment method. Instead of simply using MOFs to absorb CO 2 , ZIF-100 and CFA-1 were used to mimic CA for in situ CO 2 conversion, which provides a new prospect in the biological and industrial applications of MOFs.

Mesoporous materials, Tb-mesoMOF and MCM-41, were used to study the transport phenomena of biomolecules entering the interior pores from solution. Vitamins B 12 and B 2 were successfully encapsulated into these mesoporous materials, whereas Tb-mesoMOF (0.33 g of B 12 /g, 0.01 g of B 2 /g) adsorbed a higher amount of vitamin per mass than MCM-41 (0.21 g of B 12 /g, 0.002 g of B 2 /g). The diffusion mechanism of the biomolecules entering Tb-mesoMOF was evaluated using a mathematical model. The Raman spectroscopy studies showed vitamin B 12 has been encapsulated within Tb-mesoMOF's pores, and evaluation of the peak shifts indicated strong interactions linking vitamin B 12 's pyrroline moiety with Tb-mesoMOF's triazine and benzoate rings. Because of these stronger interactions between the vitamins and Tb-mesoMOF, longer egress times were observed than with MCM-41.

Metal-organic frameworks (MOFs) are being increasingly studied as scaffolds and supports for catalysis. The solid-state structures of MOFs, combined with their high porosity, suggest that MOFs may possess advantages shared by both heterogeneous and homogeneous catalysts, with few of the shortcomings of either. Herein, efforts to create single-site catalytic metal centers appended to the organic ligand struts of MOFs will be discussed. Reactions important for advanced energy applications, such as H2 production and CO2 reduction, will be highlighted. Examining how these active sites can be introduced, their performance, and their existing limitations should provide direction for design of the next generation of MOF-based catalysts for energy-relevant, small-molecule transformations. Finally, the introduction of second-sphere interactions (e.g., hydrogen bonding via squaramide groups) as a possible route to enhancing the activity of these metal centers is reported.

Recently, polymer-metal-organic frameworks (polyMOFs) were reported as a new class of hybrid porous materials that combine advantages of both organic polymers and crystalline MOFs. Herein, we report a bridging coligand strategy to prepare new types of polyMOFs, demonstrating that polyMOFs are compatible with additional MOF architectures besides that of the earlier reported IRMOF-1 type polyMOF. Gas sorption studies revealed that these polyMOF materials exhibited relatively high CO2 sorption but very low N2 sorption, making them promising materials for CO2/N2 separations. Moreover, these polyMOFs demonstrated exceptional water stability attributed to the hydrophobicity of polymer ligands as well as the cross-linking of the polymer chains within the MOF.

The strong interactions between microperoxidase (MP-11) and Tb-mesoMOF were identified via Raman spectroscopic studies, which revealed that MP-11 molecules interact with the framework of Tb-mesoMOF through π···π interactions between the heme of MP-11 and the conjugated triazine and benzene rings in the organic ligand of Tb-mesoMOF. The strong interactions facilitate the retention of MP-11 molecules within the metal-organic framework (MOF) pores, which is in striking contrast with the severe leaching of MP-11 from MCM-41 due to the lack of specific interactions between enzyme molecules and the mesoporous silica material.

When immersed in solutions containing Cu(II) cations, the microporous metal-organic material P11 ([Cd4(BPT)4]·[Cd(C44H36N8)(S)]·[S], BPT = biphenyl-3,4',5-tricarboxylate) undergoes a transformation of its [Cd2(COO)6](2-) molecular building blocks (MBBs) into novel tetranuclear [Cu4X2(COO)6(S)2] MBBs to form P11-Cu. The transformation occurs in single-crystal to single-crystal fashion, and its stepwise mechanism was studied by varying the Cd(2+)/Cu(2+) ratio of the solution in which crystals of P11 were immersed. P11-16/1 (Cd in framework retained, Cd in encapsulated porphyrins exchanged) and other intermediate phases were thereby isolated and structurally characterized. P11-16/1 and P11-Cu retain the microporosity of P11, and the relatively larger MBBs in P11-Cu permit a 20% unit cell expansion and afford a higher surface area and a larger pore size.