Organic Frameworks Research Articles

Direct Light-Enabled Access to α-Boryl Radicals: Application in the Stereodivergent Synthesis of Allyl Boronic Esters.

Operationally simple strategies to assemble boron containing organic frameworks are highly enabling in organic synthesis. While conventional retrosynthetic logic has engendered many platforms focusing on the direct formation of C-B bonds, α-boryl radicals have recently reemerged as versatile open-shell alternatives to access organoborons via adjacent C-C bond formation. Direct light-enabled α-activation is currently contingent on photo- or transition metal-catalysis activation to efficiently generate radical species. Here, we disclose a facile activation of α-halo boronic esters using only visible light and a simple Lewis base to enable homolytic scission. Intermolecular addition to styrenes facilitates the rapid construction of highly versatile E-allylic boronic esters. The simplicity of activation permits the strategic merger of this construct with selective energy transfer catalysis to enable the complimentary stereodivergent synthesis of Z-allylic boronic esters.

Direct Light‐Enabled Access to α‐Boryl Radicals: Application in the Stereodivergent Synthesis of Allyl Boronic Esters**

AbstractOperationally simple strategies to assemble boron containing organic frameworks are highly enabling in organic synthesis. While conventional retrosynthetic logic has engendered many platforms focusing on the direct formation of C−B bonds, α‐boryl radicals have recently reemerged as versatile open‐shell alternatives to access organoborons via adjacent C−C bond formation. Direct light‐enabled α‐activation is currently contingent on photo‐ or transition metal‐catalysis activation to efficiently generate radical species. Here, we disclose a facile activation of α‐halo boronic esters using only visible light and a simple Lewis base to enable homolytic scission. Intermolecular addition to styrenes facilitates the rapid construction of highly versatileE‐allylic boronic esters. The simplicity of activation permits the strategic merger of this construct with selective energy transfer catalysis to enable the complimentary stereodivergent synthesis ofZ‐allylic boronic esters.

A Metal‐Organic Framework Incorporating Eight Different Size Rare‐Earth Metal Elements: Toward Multifunctionality À La Carte

AbstractMulti‐metallic multivariate (MTV) rare earth (RE) metal−organic frameworks (MOFs) are of interest for the development of multifunctional materials, however examples with more than three RE cations are rare and obstructed by compositional segregation during synthesis. Herein, this work demonstrates the synthesis of a multi‐metallic MTV RE MOF incorporating two, four, six, or eight different RE ions with different sizes and in nearly equimolar amounts and no compositional segregation. The MOFs are formed by a combination of RE cations (La, Ce, Eu, Gd, Tb, Dy, Y, and Yb) and a 1,7‐di(4‐carboxyphenyl)‐1,7‐dicarba‐closo‐dodecaborane (mCB‐L) linker. The steric bulkiness and acidity of mCB‐L is crucial for the incorporation of different size RE ions into the MOF structure. Demonstration of the incorporation of all RE cations is performed via compositional and structural characterization. The more complex MTV MOF, including all eight RE ions (mCB‐8RE), are also characterized using optical, thermal, and magnetic techniques. Element‐selective X‐ray absorption spectroscopy and X‐ray Magnetic Circular Dichroism measurements allow us to characterize spectroscopically each of the eight RE ions and determine their magnetic moments. This work paves the way for the investigation of MTV MOFs with the possibility to combine RE ions à la carte for diverse applications.

Quantitative evaluation for the contribution of each component in NaYF4: Yb, Tm@NaYF4: Yb, Ho@NaYF4 upconversion nanoparticle: Active shell, inert shell, size, and their cooperation

Development of the upconversion nanoparticles/metal organic frameworks (UCNPs/MOFs) covering the full solar light spectrum, especially for the near infrared (NIR) light, is an robust strategy to improve the photocatalytic activity. However, the low upconversion efficiency is still an obstacle in the photocatalytic process. Introduction of shell to construct the core-shell or core-shell-shell upconversion nanoparticles is a feasible and popular pathway to refine the upconversion efficiency. However, the contribution of each component and their synergistic cooperation is still obscure, especially for the quantitative evaluation. A series of upconversion nanoparticles, NaYF4: Yb, Tm (TM), NaYF4: Yb, Tm@NaYF4: Yb, Ho (TM@HO), and NaYF4: Yb, Tm@NaYF4: Yb, Ho@NaYF4 (TM@HO@Y), are fabricated to account the contribution of active shell, inert shell, and their cooperation. Furthermore, the NaYF4: Yb, Tm (NYT, the size is different with that of TM) and NaYF4: Yb, Tm@NaYF4 (TM@Y) are also developed by the controlled synthesis with the same size as TM@HO@Y to avoid the size influence. According to the luminescent spectrum feature, the contribution of each part is fitted into a linear equation. By combination of NH2-UiO-66 (Zr) (NU), the hybrid photocatalysts are developed and their photocatalytic performance is measured by degradation of antibiotics and organic pollutant. This work sheds light on the quantitatively elucidating the contribution of each component, which is helpful to design the robust upconversion nanoparticles with the desired upconversion efficiency by tuning the component.

Nitrogen-coordinated cobalt embedded in hollow carbon polyhedron for catalytic ozonation of odor CH3SH at ambient temperature

Metal − organic framework (MOF) derived carbon-based nanocatalysts have received great attention in environmental remediation applications. Herein, a hollow carbon polyhedron with nitrogen-coordinated cobalt embedded has been synthesized by thermal transformation of the core–shell structure ZIF-8@ZIF-67 (marked as ZIF-8@ZIF-67-C). Remarkably, the ZIF-8@ZIF-67-C catalyst could remove almost 98% of CH3SH after running for 60 min, exceeding the reported values (about 30 times higher than that of commercial MnO2 catalysts). Elimination performance experimental results demonstrate that ZIF-8@ZIF-67-C has better anti-interference ability and anti-toxicity properties. The excellent catalytic performance can be attributed to the following facts: unique structure, high conductivity, abundant hierarchical porous structure, and accessible active sites. Theoretical calculation reveals the mechanism is that the Co-N electron bridge promotes Co nanoparticles adsorb O3, providing electrons to O3 and producing 1O2 to further oxidize CH3SH into CO2/SO42−. Also, the ZIF-8@ZIF-67-C catalyst supported on Al2O3 still shows excellent catalytic activity and durability, which deepened the practical application. This work provides a strategy for the development of MOF-on-MOF-derived metal/carbon hybrid materials in environmental applications.

Size optimization of mesoporous β-Cyclodextrin Metal-Organic frameworks as Bio-MOFs

In this study synthesis and size optimization of the β-cyclodextrin-metal–organic framework (β-CD-MOF) with potassium as the metal node through the vapor diffusion method was carried out. The effect of different solvents (methanol, ethanol, acetone, and acetonitrile), temperature (40, 50, and 60 °C), time (6, 12, and 24 h), the molar ratio of β-CD to KOH (1:4, 1:8 and 1:16) and different amount of CTAB (0, 56 and 112 mg) was investigated. One factor at a time approach was implemented and the optimum condition obtained from each parameter was used to synthesize a final crystal structure. Increasing time, temperature, and CTAB concentration reduced the size of the crystals. Methanol produced uniform morphology and smaller crystal size, and the optimum molar ratio of β-CD to KOH was obtained to be 1:8. The optimized particle had an average size of 301 ± 13 nm and surface area of 1123 m2/g, with mean pore diameter 2.2 nm.

London Dispersion Effects on the Stability of Heavy Tetrel Molecules.

London dispersion (LD) interactions, which stem from long-range electron correlations arising from instantaneously induced dipoles can occur between neighboring atoms or molecules, for example, between H atoms within ligand C-H groups. These interactions are currently of interest as a new method of stabilizing long bonds and species with unusual oxidation states. They can also limit reactivity by installing LD enhanced groups into organic frameworks or ligand substituents. Here, we address the most recent advances in the design of LD enhanced ligands, the sterically counterintuitive structures that can be generated and the consequences that these interactions can have on the structures and reactivity of sterically crowded heavy group 14 species.

Chemically Gradient Hydrogen‐Bonded Organic Framework Crystal Film

AbstractHydrogen‐bonded organic frameworks (HOFs) are ordered supramolecular solid structures, however, nothing much explored as centimetre‐scale self‐standing films. The fabrication of such crystals comprising self‐supported films is challenging due to the limited flexibility and interaction of the crystals, and therefore studies on two‐dimensional macrostructures of HOFs are limited to external supports. Herein, we introduce a novel chemical gradient strategy to fabricate a crystal‐deposited HOF film on an in situ‐formed covalent organic polymer film (Tam‐Bdca‐CGHOF). The fabricated film showed versatility in chemical bonding along its thickness from covalent to hydrogen‐bonded network. The kinetic‐controlled Tam‐Bdca‐CGHOF showed enhanced proton conductivity (8.3×10−5 S cm−1) compared to its rapid kinetic analogue, Tam‐Bdca‐COP (2.1×10−5 S cm−1), which signifies the advantage of bonding‐engineering in the same system.

Smart phosphorescence from solid to water through progressive assembly strategy based on dual phosphorescent sources

AbstractDeveloping smart room‐temperature phosphorescence (RTP) materials with facile and efficient strategies have attracted increasing attention. Herein, tunable RTP materials with two phosphorescent sources and stepwise enhanced phosphorescence in water are obtained through an in‐situ self‐assembly strategy based on the sensitization of phosphors by trimesic acid (TMA) through simple doping and the rigidification of phosphors by hydrogen‐bonded organic frameworks (HOFs). As expected, doped TMA+phosphors simultaneously promote the RTP emission of phosphors and maintain TMA phosphorescence. In‐situ assembled HOF(MA‐TMA)@phosphors facilitate smart RTP emission in water due to the coexistence of phosphorescent HOF(MA‐TMA) host and phosphors guest. Additionally, such RTP materials with good processability demonstrate the application potential in information security, benefitting from their varied afterglow lifetimes and easy luminous recognition in the darkness. This work will inspire the design of dual phosphorescent source RTP systems and provide new strategies for the development of smart RTP materials in water.

A Water-Stable 3D Eu(III)-Organic Framework as a Bi-Functional Ratiometric Luminescent Sensor for Fast, Sensitive and Selective Detection of ODZ and Hg2+ in Aqueous Media

The fast, sensitive and selective detection of some antibiotics and heavy metal cations in water is highly desirable for environmental protection and human health, but it is still currently challenging. In this work, a new luminescent Eu(III)-based metal-organic framework (MOF), {[(CH3)2NH2][Eu(L)2(H2O)2]·xDMF}n (1) [H2L = 4,4’-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid], was solvothermally synthesized. Complex 1 exhibits good water stability and luminescent property and could serve as a bifunctional ratiometric luminescent sensor for fast, sensitive and selective detection of ornidazole (ODZ) and Hg2+ in aqueous solution. The corresponding luminescent mechanism has also been discussed. This work indicates that 1 as a promising luminescent material exhibits luminescent quenching behavior for ODZ and luminescent enhancement behavior for Hg2+ in H2O, which will promote the practical application of Ln-MOF-based ratiometric luminescent sensors in monitoring antibiotics and metal ions pollutants in the environmental water matrices.

Chitosan decorated zirconium metal-organic framework for collaborative adsorption and photocatalytic degradation of methylene blue and methyl orange

A type of crystalline porous material known as zirconium metal-organic frameworks (UiO-66) is made up of organic carboxylate ligands and inorganic zirconium clusters. The UiO-66 has consistent pore sizes, large porosities, exceptional adsorption capabilities, and particular functional groups for increasing dye adsorption. This study reports the synthesis of Zirconium metal-organic framework (UiO-66) and chitosan composite of zirconium metal−organic framework (CS/UiO-66) for potential adsorption of methyl orange (MO) and methylene blue (MB) dyes from the aqueous media and additional, excellent photodegradation capability of the synthesized material towards selected dyes. The synthesized materials were successfully characterized for structural, morphological, surface and thermogravimetrical analysis. The exclusion of dyes onto the CS/UiO-66 followed the trend MB (2321 mg/g) > MO (900 mg/g) respectively. The maximum sorption and degradation capacity of the CS/UiO-66 were increased by 5–10 times after its composite with chitosan (CS) and the affinity of the dyes towards the different adsorbents followed the sequence CS/UiO-66 > UiO-66 > CS which is parallel to their surface properties. The negative values of the entropy i.e., − 382 for MB and − 249 for MO affirmed the controlled versatility of the MO, and MB onto CS/UiO-66 whereas the isosteric heat of adsorption i.e., − 201 kJ/mol for MB and − 153 kJ/mol for MO illustrated the exothermicity of the adsorption process. The intraparticle diffusion and Richenberge kinetic models demonstrated that pore diffusion dominates in the adsorption of MB while film diffusion has a greater involvement in the MO adsorption of CS/UiO-66. Moreover, the photocatalytic degradation study indicated that the pH and H2O2 play a significant part in the deprivation of dyes. While GC-MS analysis revealed that the photocatalytic degradation of MB resulted in the formation of six TPs. The toxicity of these TPs of MB was evaluated by ECOSAR program and the results showed that the TPs were less toxic than the parent MB molecule.

A phase 1 dose-escalation study of RiMO-301 with palliative radiation in advanced tumors.

2527 Background: Nanoscale metal−organic frameworks (MOFs) are a new class of organic−inorganic hybrid nanomaterials constructed from metal centers and organic ligands. Preclinical studies have shown that nanoscale MOFs can enhance the antitumor effects of ionizing radiation via a unique radiotherapy-radiodynamic therapy mode of action, and MOFs plus radiation can enhance the immunotherapeutic effects of immune checkpoint inhibitors. RiMO-301 is a hafnium-based MOF which enhances radiotherapy and checkpoint blockade immunotherapy without showing systemic toxicity in preclinical models. RiMO-301 is the first MOF to enter clinical trials on human patients. Methods: This is a multicenter, open-label, first-in-human dose-escalation phase I trial of RiMO-301 [NCT03444714]. The primary objective is to determine the maximum tolerated dose (MTD) of locally injected RiMO-301 with or without the PD-1 inhibitor pembrolizumab in patients treated with concurrent palliative doses of radiation (20 Gy in 5 fractions or 30 Gy in 10 fractions) using a 3+3 design. The MTD is defined as the dose associated with dose-limiting toxicity (DLT) in less than 33% of patients. The secondary objective is to evaluate antitumor response (objective response rate, ORR) using RECIST and itRECIST criteria. Results: A total of 25 patients were enrolled and treated with escalating doses of RiMO-301 (relative to tumor volumes). No protocol defined DLT was reported. The observed possibly treatment related adverse events included mild dermatitis radiation, mild dysgeusia, diarrhea, mild hypotension (30 days post treatment) and mild dizziness (30 days post treatment). One patient each experienced a Grade 2 alanine aminotransferase increase 45 days post treatment, a Grade 2 dry mouth, and a Grade 3 pain at the injection site. Nineteen patients were evaluable, with 13 and 6 patients, respectively, for RiMO-301 without and with pembrolizumab treatments. By itRECIST criteria, RiMO-301 without pembrolizumab demonstrated 38.5% (5/13) ORR (1 complete response and 4 partial responses) with 2 additional patients experiencing 20-30% tumor size reduction. RiMO-301 with pembrolizumab exhibited 66.7% (4/6) ORR with the 2 remaining patients showing 15-20% tumor size reduction. Preliminary pharmacokinetic analysis indicated that the hafnium concentrations in the systemic circulation were either below or barely above the level of detection. Conclusions: RiMO-301 with or without pembrolizumab was well tolerated and demonstrated promising signs of efficacy in patients with advanced tumors when treated with concurrent palliative radiotherapy. The results support the use of RiMO-301 as a potential radio-enhancer and will prompt further phase 2 studies in the development of RiMO-301 for patients undergoing radiotherapy. Clinical trial information: NCT03444714 .

Cover Picture

The cover picture shows the second example of tetravalent plutonium carboxyl‐based organic framework, termed as PuTPO. While PuTPO can maintain high crystallinity within several months after synthesis, it exhibits a radiation‐induced swelling effect probed by the expansion of cell parameter of b axis after self‐irradiation from α‐decay of 242Pu. More details are discussed in the article by Wang et al. on page 1552—1556.image

Control of morphology of covalent organic framework-5 for chemiresistive low-temperature ammonia sensors

Covalent organic frameworks (COFs) have attracted much attention due to their unique structures and properties. However, the morphology regulation of COFs has always been a challenge, and the application field of COFs need to be further explored. Herein, three different regular morphologies of COF-5 crystals, including nanoparticles, nanorods and nanosheets, are firstly regulated by adjusting the reaction parameters under the convenient and mild conditions. The molecular configuration and pore size distribution of the as-prepared COF-5 crystals were revealed by DFT calculation and experimental tests. The ammonia sensing test proves that all three COF-5 crystals with different morphologies have good response at room temperature, and COF-5 nanosheets with maximum specific surface area possess the lowest detection limit of 600 ppb towards ammonia gas. Furthermore, COF-5 crystals-based gas sensors have excellent reversibility, gas selectivity and long-term stability. Gas sensing mechanism illustrates that abundant boronate esters with Lewis acidity of COF-5 crystals act as the active site to realize the ammonia sensitive detection.

A thiazolothiazole based Zn(II) metal−organic framework with multi-responsive fluorescent sensing toward Al3+ and oxoacid anions in an aqueous solution

Luminescent metal−organic frameworks(LMOFs) have been utilized to identify dangerous and toxic contaminants, biomarkers, and biological species. However, the luminescent properties in MOFs have been limited by the organic connectors. In this study, we present a Zn-MOF based on thiazolothiazole ligand, which exhibits fluorescent sensing properties through a mixed bipyridine-dicarboxylate strategy. {[Zn2(NDC)2(4bppyttz)]·1.5DMF} (MOF 1) (4bppyttz=2,5-bis(4-(pyridin-4-yl)phenyl)thiazolo[5,4-d]thiazole, H2NDC=naphthalene-2,6-dicarboxylic acid) featured a three-fold interpenetrated pillared layer structure in the crystal structure. The fluorescent detection of Al3+ can be served as the turn-on effect and oxoacid anions such as CrO42−, Cr2O72−, and MnO4− can be served as turn-off effects. Furthermore, luminescence sensing studies demonstrated that MOF 1 showed high selectivity and multi-responsiveness primarily for Al3+, CrO42−, MnO4−, and Cr2O72− in an aqueous medium, with detection limits of 2.9, 3.4, 3.0, and 2.2 μM, respectively. To explain the quenching and enhancing mechanisms, XRD, absorption spectra, IR spectra, and theoretical calculations were discussed. Additionally, MOF-coated test strips were utilized to detect these ions, exhibiting excellent agreement with fluorescence spectroscopy. This work may offer a promising foundation for future thiazolothiazole-based MOFs applications in the detection of numerous contaminants.

Allosteric probe-triggered isothermal amplification to activate CRISPR/Cas12a for sensitive electrochemiluminescence detection of Salmonella

We report an electrochemiluminescence (ECL) sensor for Salmonella detection based on allosteric probe as a bio-recognition element and CRISPR/Cas12a as a signal amplification strategy. In the presence of Salmonella, the structure switching occurs on allosteric probes, resulting in their hybridization with primers to trigger isothermal amplification. Salmonella is then released to initiate the next reaction cycle accompanying by generating a large amount of dsDNA, which are subsequently recognized by CRISPR-gRNA for activating the trans-cleavage activity of Cas12a. Furthermore, the activated Cas12a can indiscriminately cut the ssDNA which is bound to the electrode, enabling the release of the ECL emitter porphyrinic Zr metal − organic framework (MOF, PCN-224) and exhibiting a decreased ECL signal accordingly. The linear range is 50 CFU·mL−1–5 × 106 CFU·mL−1 and the detection limit is calculated to be 37 CFU·mL−1. This method sensitively detects Salmonella in different types of real samples, indicating it is a promising strategy for Salmonella detection

Highly Selective Photosynthesis of Formic Acid by Unifying the Products of CO2 Reduction and Methanol Oxidation

Photocatalytic conversion of CO2 to added‐value fuels or chemicals is a promising technology for the effective utilization of the disturbing greenhouse gas, but its economic benefit is limited either by low efficiency due to the difficulty of water oxidation or by the employment of expensive sacrificial reagents. To overcome this dilemma, herein, an effective strategy is reported for the resourceful utilization of CO2 by creating an eco‐friendly bifunctional photocatalyst to achieve CO2 photoreduction concurrent with methanol photooxidation to the uniform product of formic acid for the first time. The bifunctional photocatalyst is elaborately constructed by in situ encapsulating lead‐free double perovskite (Cs2AgBiBr6, abbreviated as CABB) nanocrystals into the pores of Fe‐based metal−organic framework (MIL‐101(Fe)). The tight contact between CABB and MIL‐101(Fe) in the resultant CABB/MIL‐101(Fe) composite facilitates the efficient spatial separation of photogenerated carriers, which leads to the division of reduction and oxidation functional units. CABB/MIL‐101(Fe) composites can unify the redox products into formic acid, reaching an impressive formation yield of 1375 μmol g−1 h−1 with a high selectivity of 97.8%. This work provides a viable strategy for the efficient photosynthesis of formic acid, promoting the cost‐effective utilization of CO2.

Tuning Pore Polarization to Boost Ethane/Ethylene Separation Performance in Hydrogen‐Bonded Organic Frameworks

AbstractHydrogen‐bonded organic frameworks (HOFs) show great potential in energy‐saving C2H6/C2H4 separation, but there are few examples of one‐step acquisition of C2H4 from C2H6/C2H4 because it is still difficult to achieve the reverse‐order adsorption of C2H6 and C2H4. In this work, we boost the C2H6/C2H4 separation performance in two graphene‐sheet‐like HOFs by tuning pore polarization. Upon heating, an in situ solid phase transformation can be observed from HOF‐NBDA(DMA) (DMA=dimethylamine cation) to HOF‐NBDA, accompanied with transformation of the electronegative skeleton into neutral one. As a result, the pore surface of HOF‐NBDA has become nonpolar, which is beneficial to selectively adsorbing C2H6. The difference in the capacities for C2H6 and C2H4 is 23.4 cm3 g−1 for HOF‐NBDA, and the C2H6/C2H4 uptake ratio is 136 %, which are much higher than those for HOF‐NBDA(DMA) (5.0 cm3 g−1 and 108 % respectively). Practical breakthrough experiments demonstrate HOF‐NBDA could produce polymer‐grade C2H4 from C2H6/C2H4 (1/99, v/v) mixture with a high productivity of 29.2 L kg−1 at 298 K, which is about five times as high as HOF‐NBDA(DMA) (5.4 L kg−1). In addition, in situ breakthrough experiments and theoretical calculations indicate the pore surface of HOF‐NBDA is beneficial to preferentially capture C2H6 and thus boosts selective separation of C2H6/C2H4.

Rücktitelbild: Metal‐Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical‐Mediated Reactions (Angew. Chem. 21/2023)

A binap-ligated copper iodide dimer embedded on a metal−-organic framework (MOF) was designed as an effective photoredox catalyst by Dan Li, Jian He, and co-workers in their Research Article (e202300233). Under visible-light irradiation, this heterogenized copper(I) complex promotes multiple iminyl radical-mediated reactions initiated by N−O bond cleavage, with significantly enhanced photocatalytic activity compared to its homogeneous counterparts. The use of a hydroxamic acid linker for post-synthetic modification renders the catalyst recyclable.

Back Cover: Metal‐Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical‐Mediated Reactions (Angew. Chem. Int. Ed. 21/2023)

A binap-ligated copper iodide dimer embedded on a metal−organic framework (MOF) was designed as an effective photoredox catalyst by Dan Li, Jian He, and co-workers in their Research Article (e202300233). Under visible-light irradiation, this heterogenized copper(I) complex promotes multiple iminyl radical-mediated reactions initiated by N−O bond cleavage, with significantly enhanced photocatalytic activity compared to its homogeneous counterparts. The use of a hydroxamic acid linker for post-synthetic modification renders the catalyst recyclable.