Rapid synthesis of aminal-linked covalent organic frameworks for CO2/CH4 separation.

As an emerging category of crystalline porous materials, covalent organic frameworks (COFs) are primarily synthesized via solvothermal methods. However, achieving rapid synthesis of COFs through this approach poses a significant challenge. To address the issue of slow synthesis, we studied the crystallization process of aminal-linked COFs via the condensation of a cost-effective aldehyde and secondary amine, and successfully expedited the synthesis of COFs within a one-hour duration. Furthermore, gram-scale aminal-linked COFs with abundant ultra-microporous channels demonstrated promising potential for CO2/CH4 separation. This study enables the rapid synthesis of aminal-linked COFs from cheap raw materials, which lays a foundation for their practical applications.

Identification of two-dimensional covalent organic frameworks with mcm topology and their application in photocatalytic hydrogen evolution.

Covalent organic frameworks have attracted considerable attention in recent years as a distinct class of crystalline porous organic materials. Their functional properties are inherently linked to their structural characteristics. Although hundreds of COFs have been reported so far, the types of their topologic structure are still limited. In this article, we report the identification of mcm topology for three porphyrin-based two-dimensional COFs, which are constructed from [4 + 4] imine condensation reactions. The mcm net is generated by pentagonal tiling, which has not been identified for COFs before. The structure of the COFs is elucidated by a variety of experimental characterization and structural simulations, by which their reticular frameworks exclusively composed of pentagonal pores have been confirmed. Moreover, the COFs exhibit high performance in photocatalytic hydrogen evolution from water, with the best one up to 10.0 mmol g-1 h-1 after depositing 0.76 wt% Pt as a co-catalyst. This study identifies mcm topology for COFs for the first time and highlights the potential of these COFs as promising photocatalysts for sustainable hydrogen production from water.

An Azulene-Based Crystalline Porous Covalent Organic Framework for Efficient Photothermal Conversion.

The designed synthesis of a crystalline azulene-based covalent organic framework (COF-Azu-TP) is presented and its photothermal property is investigated. Azulene, a distinctive 5-7 fused ring non-benzenoid aromatic compound with a large intramolecular dipole moment and unique photophysical characteristics, is introduced as the key feature in COF-Azu-TP. The incorporation of azulene moiety imparts COF-Azu-TP with broad-spectrum light absorption capability and interlayer dipole interactions, which makes COF-Azu-TP a highly efficient photothermal conversion material. Its polyurethane (PU) composite exhibits a solar-to-vapor conversion efficiency (97.2%) and displays a water evaporation rate (1.43 kg m-2 h-1) under one sun irradiation, even at a very low dosage of COF-Azu-TP (2.2 wt%). Furthermore, COF-Azu-TP is utilized as a filler in a polylactic acid (PLA)/polycaprolactone (PCL) composited shape memory material, enabling rapid shape recovery under laser stimulation. A comparison study with a naphthalene-based COF isomer further emphasizes the crucial role of azulene in enhancing photothermal conversion efficiency. This study demonstrates the significance of incorporating specific building blocks into COFs for the development of functional porous materials with enhanced properties, paving the way for future applications in diverse fields.

Converting an amorphous covalent organic polymer to a crystalline covalent organic framework mediated by a repairing agent.

We herein report a new approach to converting an amorphous covalent organic polymer to a crystalline heteropore covalent organic framework (COF), which is promoted by using an additive for structure repair. This provides a new method for the construction of COFs from cross-linked polymers.

Syntheses of Covalent Organic Frameworks via a One-Pot Suzuki Coupling and Schiff's Base Reaction for C2 H4 /C3 H6 Separation.

Covalent organic frameworks (COFs) featuring permanent porosity, designable topologies, and tailorable functionalities have attracted great interest in the past two decades. Developing efficient modular approaches to rationally constructing COFs from a set of molecules via covalent linking has been long pursued. Herein, we report a facile one-pot strategy to prepare COFs via an irreversible Suzuki coupling reaction followed by a reversible Schiff's base reaction without the need for intermediate isolation. Gram-scale ordered frameworks with kgm topology and rich porosities can be obtained by using diamino-aryl halide and dialdehyde aryl-borate compounds as monomers. The resultant microporous CR-COFs were used for efficient C2 H4 /C3 H6 separation. This strategy reduces the waste generated and efforts consumed by stepwise reactions and relative purification processes, making the large-scale syntheses of stable COFs feasible. Moreover, it offers a novel modular approach to designing COF materials.

A Facile, Efficient, and General Synthetic Method to Amide-Linked Covalent Organic Frameworks.

Amide-linked covalent organic frameworks (amide COFs) possess enormous potentials in practical applications benefiting from their high stability and polyamide structures. However, they suffer from very limited accessibility. Herein, we report a new linkage conversion method to rapidly synthesize crystalline amide COFs through oxidation of imine linkages in their corresponding imine-linked frameworks with KHSO5 as an oxidant under very mild conditions. This synthetic strategy is general, facile, efficient, and scalable, as demonstrated by the procedure of simply stirring mixtures of imine-linked COFs (seven examples) and KHSO5 in anhydrous dimethylformamide for several hours to complete the conversions and gram-scale synthesis. The high efficiency of this approach enables facile production of amide COFs from widely available imine-linked COFs, which lays the foundation for exploring practical applications of this unique type of polyamide material.

A Covalent Organic Framework with Extended π-Conjugated Building Units as a Highly Efficient Recipient for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have recently become a research hotspot because of their tempting theoretical capacity and energy density. Nevertheless, the notorious shuttle of polysulfides hinders the advancement of Li-S batteries. Herein, a two-dimensional covalent organic framework (COF) with extended π-conjugated units has been designed, synthesized, and used as sulfur recipients with 88.4 wt % in loading. The COF offers an elaborate platform for sufficient Li-S redox reactions with almost theoretical capacity release (1617 mA h g-1 at 0.1 C), satisfactory rate capability, and intensively traps polysulfides for a decent Coulombic efficiency (ca. 98.0%) and extremely low capacity decay (0.077% per cycle after 528 cycles at 0.5 C). The structural factors of the COF on the high-performance batteries are revealed by density functional theory calculations to be the high degrees of conjugation and proper interlayer space. This work not only demonstrates the great potential of COFs as highly efficient sulfur recipients but also provides a viable guidance for further design of COF materials to tackle shuttling issues toward active materials in electrochemical energy storage.

Materials genomics methods for high-throughput construction of COFs and targeted synthesis.

Materials genomics represents a research mode for materials development, for which reliable methods for efficient materials construction are essential. Here we present a methodology for high-throughput construction of covalent organic frameworks (COFs) based on materials genomics strategy, in which a gene partition method of genetic structural units (GSUs) with reactive sites and quasi-reactive assembly algorithms (QReaxAA) for structure generation were proposed by mimicking the natural growth processes of COFs, leading to a library of 130 GSUs and a database of ~470,000 materials containing structures with 10 unreported topologies as well as the existing COFs. As a proof-of-concept example, two generated 3D-COFs with ffc topology and two 2D-COFs with existing topologies were successfully synthesized. This work not only presents useful genomics methods for developing COFs and largely extended the COF structures, but also will stimulate the switch of materials development mode from trial-and-error to theoretical prediction-experimental validation.

Synthesis and Reactivity of a Scandium Terminal Hydride: H2 Activation by a Scandium Terminal Imido Complex.

Dihydrogen is easily activated by a scandium terminal imido complex containing the weakly coordinated THF. The reaction proceeds through a 1,2-addition mechanism, which is distinct from the σ-bond metathesis mechanism reported to date for rare-earth metal-mediated H2 activation. This reaction yields a scandium terminal hydride, which is structurally well-characterized, being the first one to date. The reactivity of this hydride is reported with unsaturated substrates, further shedding light on the existence of the terminal hydride complex. Interestingly, the H2 activation can be reversible. DFT investigations further eludciate the mechanistic aspects of the reactivity of the scandium anilido-terminal hydride complex with PhNCS but also on the reversible H2 activation process.

Lewis acid triggered reactivity of a Lewis base stabilized scandium-terminal imido complex: C-H bond activation, cycloaddition, and dehydrofluorination.

A stable scandium-terminal imido complex is activated by borane to form an unsaturated terminal imido complex by removing the coordinated Lewis base, 4-(dimethylamino)pyridine, from the metal center. The ensuing terminal imido intermediate can exist as a THF adduct and/or undergo cycloaddition reaction with an internal alkyne, C-H activation of a terminal alkene, and dehydrofluorination of fluoro-substituted benzenes or alkanes at room temperature. DFT investigations further highlight the ease of C-H activation for terminal alkene and fluoroarene. They also shed light on the mechanistic aspects of these two reactions.