Charge Separation in Metal-Organic Framework Enables Heterogeneous Thiol Catalysis.

Photoinduced metal-organic framework (MOF) enabled heterogeneous thiol catalysis has been achieved for the first time. MOF Zr-TPDCS-1, consisting of Zr6 -clusters and TPDCS linkers (TPDCS=3,3'',5,5''-tetramercapto[1,1':4',1''-terphenyl]-4,4''-dicarboxylate), effectively catalyzed the borylation, silylation, phosphorylation, and thiolation of organic molecules. Upon irradiation, the fast electron transfer from TPDCS to Zr6 -cluster is believed to facilitate the formation of the thiyl radical, a hydrogen atom transfer catalyst, which competently abstracts the hydrogen from borane, silane, phosphine, or thiol for generating the corresponding element radical to engender the chemical transformations. The elaborate control experiments evidenced the generation of thiyl radicals in MOF and illustrated a radical reaction pathway. The gram-scale reaction worked well, and the product was conveniently separated via centrifugation and vacuum with a turnover number (TON) of ≈3880, highlighting the practical application potential of heterogeneous thiyl-radical catalysis.

Correction to Covalent Triazine Frameworks Embedded with Ir Complexes for Enhanced Photocatalytic Hydrogen Evolution.

[This corrects the article DOI: 10.1021/acsaem.2c00977.].

Linker Deficiency, Aromatic Ring Fusion, and Electrocatalysis in a Porous Ni8-Pyrazolate Network.

The cruciform linker molecule here features two designer functions: the pyrazole donors for framework construction, and the vicinal alkynyl units for benzannulation to form nanographene units into the Ni8-pyrazolate scaffold. Unlike the full 12 connections of the Ni8(OH)4(H2O)2 clusters in other Ni8-pyrazolate networks, significant linker deficiency was observed here, leaving about half of the Ni(II) sites capped by acetate ligands, which can be potentially removed to open the metal sites for reactivity. The crystalline Ni8-pyrazolate scaffold also retains the crystalline order even after thermal treatments (up to 300 °C) that served to partially graphitize the neighboring alkyne units. The resultant nanographene components enhance the electroactive properties of the porous hosts, achieving hydrogen evolution reaction (HER) activity that rivals that of topical nickel/palladium-enabled materials.

A Stable 2D Zr(IV)-Based Metal-Organic Framework (USTS-7) for Selective Sensing of Cr2O72- in Aqueous Solution.

A novel 2D porous Zr(IV)-based metal-organic framework (USTS-7) was assembled from 2,5-bis[2-(methylthio)ethylthio]terephthalic acid and ZrCl4. USTS-7 retains its stability in water, strong acid, and base; moreover, it is highly luminescent and displays a remarkable selective sensing property toward Cr2O72- in aqueous solution with a very low detection limit.

Donor-acceptor covalent organic frameworks of nickel(II) porphyrin for selective and efficient CO2 reduction into CO.

Donor-acceptor two-dimensional covalent organic frameworks, PD-COF-23 and PD-COF-23-Ni, are constructed and applied for selective CO2 reduction with CO conversion rates of 20.9 µmol g-1 h-1 and 40.0 µmol g-1 h-1, respectively, in the absence of any additional photosensitizers and noble metal co-catalysts within an operation time of 25 h. The multilayer nanosheet structure, efficient charge separation and transport, and internal reductive quenching cycle of the NiTAPP fragments of PD-COF-23-Ni result in its higher photocatalytic efficiency than that of PD-COF-23.

2D metal-organic framework for stable perovskite solar cells with minimized lead leakage.

Despite the notable progress in perovskite solar cells, maintaining long-term operational stability and minimizing potentially leaked lead (Pb2+) ions are two challenges that are yet to be resolved. Here we address these issues using a thiol-functionalized 2D conjugated metal-organic framework as an electron-extraction layer at the perovskite/cathode interface. The resultant devices exhibit high power conversion efficiency (22.02%) along with a substantially improved long-term operational stability. The perovskite solar cell modified with a metal-organic framework could retain more than 90% of its initial efficiency under accelerated testing conditions, that is continuous light irradiation at maximum power point tracking for 1,000 h at 85 °C. More importantly, the functionalized metal-organic framework could capture most of the Pb2+ leaked from the degraded perovskite solar cells by forming water-insoluble solids. Therefore, this method that simultaneously tackles the operational stability and lead contamination issues in perovskite solar cells could greatly improve the feasibility of large-scale deployment of perovskite photovoltaic technology.

Porphyrin Grafting on a Mercapto-Equipped Zr(IV)-Carboxylate Framework Enhances Photocatalytic Hydrogen Production.

We employ facile aromatic nucleophilic substitution between the mercapto (-SH) and arylfluoro (Ar-F) groups to achieve extensive and robust cross-linking of a coordination host by porphyrin guests that also serve the purpose of versatile postsynthetic functionalization. For this, a tritopic linker with three trident-like thiol-flanked carboxyl units are reacted with ZrOCl2·8H2O to afford a two-dimensional (3,6-connected) net. The wide aperture of the porous framework solid, together with its stability in both air and boiling water, facilitates the entry of bulky metalloporphyrin guests and the subsequent property studies. On the porphyrin side, four pentafluorophenyl (C6F5-) groups offer multiple fluoro groups to facilitate their replacement by the thiol groups from the host net. The inserted metalloporphyrin bridges impart to the metal-organic framework (MOF) host stable and recyclable activities for photocatalytic hydrogen production. We also disclose an improvement in synthetic methodology, in which BBr3 is used to simultaneously cleave the ester and benzyl thioether groups to more efficiently access thiol-equipped carboxylic acid building block.

A Bumper Crop of Boiling-Water-Stable Metal-Organic Frameworks from Controlled Linker Sulfuration.

The series of highly stable porous solids here feature systematic, regiospecific sulfur substitutions on the organic linkers for versatile functions. One major surprise lies in the controllable sequential reactions between sodium thiomethoxide (NaSMe) and octafluorobiphenyl-4,4'-dicarboxylic acid (H2bpdc-8F; this was readily made without precious metal catalysts). Namely, 3, 4, 6, and 8 methylthio-substitutions can be respectively achieved with regiospecificity (i.e., to produce the four molecules H2bpdc-3S5F, H2bpdc-4S4F, H2bpdc-6S2F, H2bpdc-8MS). A second surprise lies in their persistent formation of the UiO-67-type net with Zr(IV) ions, e.g., even in the case of the fully sulfurated H2bpdc-8MS. In addition to the remarkable breadth of functional control, all the Zr(IV)-based crystalline solids here are stable in boiling water (e.g., for 24 h) and in air as solventless, activated porous solids. Moreover, the thioether groups allow for convenient H2O2 oxidation to fine-tune the hydrophilicity and luminescence properties and improve proton conductivity.

High-Performance Metal-Organic Framework-Templated Sorbent for Selective Eu(III) Capture.

A stable porous sorbent M1 was achieved through the specific transformation of flexible thioalkyl groups and metal cluster sites in a zirconium MOF (metal-organic framework; Zr-L) template. The target polymer combines sulfoxide/sulfone and phosphoric acid in a single framework, which was fully characterized by 1H-NMR, PXRD, IR, and elemental analysis. When employed as the heavy metal adsorbent, M1 exhibit a remarkable Eu(III) sorption behavior, achieving both high chemical affinity (K d = 105) and sorption capacity (the maximum Eu(III) sorption capacity reached 220 mg g-1 at pH = 4.0 and T = 298 K calculated from the Langmuir model). Recyclability and selectivity test of M1 further prove that the sorbent is highly stable and effective for europium enrichment in the aqueous solution. This work takes focus on the introduction of multifunctional groups into a single polymeric framework in a feasible and environmentally friendly way and highlights the sorption efficiency for europium removal from the aqueous solution.

Dense Alkyne Arrays of a Zr(IV) Metal-Organic Framework Absorb Co2(CO)8 for Functionalization.

Finely dispersed Co(0) and CoO species were efficiently loaded into a stable metal-organic framework to impart catalytic activities to the porous solid. The metalation of the MOF host is facilitated by the dense arrays of accessible alkyne units that boost the alkyne-Co2(CO)8 interaction. The tetrakis(4-carboxylphenylethynyl)pyrene linker, with eight symmetrically backfolded alkyne side arms, features strong fluorescence and a dendritic Sierpinski shape. The resultant Zr(IV)-MOF features NU-901 topology (scu net, with rhombus channels) and breathing properties (e.g., the contracted (porous) phase reverts to the as-made phase upon contact with DMF (dimethylformamide)). The inserted Co2(CO)8 guests quickly react with air to form atomically dispersed CoO species (nondiffracting), and subsequent thermal treatment at 600 °C of the CoO-loaded solid generates an electrocatalyst for the oxygen evolution reaction (OER).

A Thiol-Functionalized UiO-67-Type Porous Single Crystal: Filling in the Synthetic Gap.

Thiol groups (-SH) offer versatile reactivity for functionalizing metal-organic frameworks, and yet thiol-equipped MOF solids remain underexplored due to synthetic challenges. Building on the recent breakthrough using benzyl mercaptan as the sulfur source and AlCl3 for uncovering the thiol function, we report on the thiol-equipped linker 3,3'-dimercaptobiphenyl-4,4'-dicarboxylic acid and its reaction with Zr(IV) ions to form a UiO-67-type MOF solid with distinct functionalities. The thiol-equipped UiO-67 scaffold shows substantial stability toward oxidation, e.g., it can be treated with 30% H2O2 to afford oxidation of the thiol to the strongly acidic sulfonic function while maintaining the ordered porous MOF structure. The thiol groups also effectively take up palladium(II) ions from solutions to allow for comparative studies on catalytic activities and to help elucidate how the spatial configuration of the thiol groups can be engineered to impact the performance of heterogeneous catalysis in the solid state. Comparative studies on the stability in the solventless (activated) state also help to highlight the steric factor in stabilizing UiO-67-type frameworks.

Dramatic improvement of stability by in situ linker cyclization of a metal-organic framework.

We employ a two-step strategy for accessing crystalline porous covalent networks of highly conjugated π-electron systems. For this, we first assembled a crystalline metal-organic framework (MOF) precursor based on Zr(iv) ions and a linear dicarboxyl linker molecule featuring backfolded, highly unsaturated alkyne backbones; massive thermocyclization of the organic linkers was then triggered to install highly conjugated, fused-aromatic bridges throughout the MOF scaffold while preserving the crystalline order. The formation of cyclized carbon links not only greatly strengthens the precursor coordination scaffold, but also, more importantly, enhances electroactivity and charge transport throughout the polycyclic aromatic grid.