Reticular Chemistry Research Articles

Hierarchical Microtubular Covalent Organic Frameworks Achieved by COF-to-COF Transformation.

Pore environment and aggregated structure play a vital role in determining the properties of porous materials, especially regarding the mass transfer. Reticular chemistry imparts covalent organic frameworks (COFs) with well-aligned micro/mesopores, yet constructing hierarchical architectures remains a great challenge. Herein, we reported a COF-to-COF transformation methodology to prepare microtubular COFs. In this process, the C3 -symmetric guanidine units decomposed into C2 -symmetric hydrazine units, leading to the crystal transformation of COFs. Moreover, the aggregated structure and conversion degree varied with the reaction time, where the hollow tubular aggregates composed of mixed COF crystals could be obtained. Such hierarchical architecture leads to enhanced mass transfer properties, as proved by the adsorption measurement and chemical catalytic reactions. This self-template strategy was successfully applied to another four COFs with different building units.

Tuning excited state electronic structure and charge transport in covalent organic frameworks for enhanced photocatalytic performance

Covalent organic frameworks (COFs) represent an emerging class of organic photocatalysts. However, their complicated structures lead to indeterminacy about photocatalytic active sites and reaction mechanisms. Herein, we use reticular chemistry to construct a family of isoreticular crystalline hydrazide-based COF photocatalysts, with the optoelectronic properties and local pore characteristics of the COFs modulated using different linkers. The excited state electronic distribution and transport pathways in the COFs are probed using a host of experimental methods and theoretical calculations at a molecular level. One of our developed COFs (denoted as COF-4) exhibits a remarkable excited state electron utilization efficiency and charge transfer properties, achieving a record-high photocatalytic uranium extraction performance of ~6.84 mg/g/day in natural seawater among all techniques reported so far. This study brings a new understanding about the operation of COF-based photocatalysts, guiding the design of improved COF photocatalysts for many applications.

Stepwise Amplification of Circularly Polarized Luminescence in Chiral Metal Cluster Ensembles.

Chiral metal-organic frameworks(MOFs)are usually endowed by chiral linkers and/or guests. The strategy using chiral secondary building units in MOFsfor solving the trade-off of circularly polarized luminescence (CPL)-active materials, high photoluminescence quantum yields (PLQYs) and high dissymmetry factors (|glum |) has not been demonstrated. This work directionally assembles predesigned chiral silver clusters with ACQ linkers through reticular chemistry. The nanoscale chirality of the cluster transmits through MOF's framework, where the linkers are arranged in a quasi-parallel manner and are efficiently isolated and rigidified. Consequently, this backbone of chiral cluster-based MOFs demonstrates superb CPL, high PLQYs of 50.3%, and |glum | of 1.2 × 10-2 . Crystallographic analyses and DFT calculations show the quasi-parallel arrangement manners of emitting linkers leading to a large angle between the electric and magnetic transition dipole moments, boosting CPL response. As compared, an ion-pair-direct assembly without interactions between linkers induces one-ninth |glum | and one-sixth PLQY values, further highlighting the merits of directional arrangement in reticular nets. In addition, a prototype CPL switching fabricated by a chiral framework is controlled through alternating ultraviolet and visible light. This work is expected to inspire the development of reticular chemistry for high-performance chiroptical materials.

Two Stable Sodalite-Cage-Based MOFs for Highly Gas Selective Capture and Conversion in Cycloaddition Reaction.

Stable metal-organic frameworks, containing periodically arranged nanosized cages or pores and active Lewis acid-base sites, are considered ideal candidates for efficient heterogeneous catalysis. Herein, based on the light of reticular chemistry design principles, the ingenious assembly of two pyridine N-rich multifunctional triangular linkers, H3TBA [3,5-di (1h-tetrazol-5-yl) benzoic acid] and H2TZI [5-(1H-tetrazol-5-yl)isophthalic acid], with MnII formed PCP-33(Mn) and PCP-34(Mn), respectively. PCP-33(Mn) and PCP-34(Mn) are typical sod topology zeolitic metal-organic frameworks (ZMOFs) with hierarchical tetragonal micropores and metal organic polyhedral sodalite-like cages. The inner walls of these cages are modified by open metal sites MnII and Lewis acid-base sites of halide ions and N pyridine atoms. The characteristics of the cages' structures make two MOFs exhibit high surface area and a small window, which promote their outstanding gas capture ability (C2H2, 131.8 cm3 g-1; CO2, 77.9 cm3 g-1 at 273 K) and selective separation performance (C2H2/CH4, 226.2, CO2/CH4, 50.3 at 298 K), and are also suitable as catalytic reactors for metal/solvent-free chemical fixation of CO2 with epoxides to achieve high-efficiency CO2 conversion. Furthermore, they are greatly recyclable for several cycles while retaining their structural rigidity and catalytic activity.

Covalent Organic Frameworks as Emerging Nonlinear Optical Materials.

The vastness of organic synthetic strategies and knowledge of reticular chemistry have made covalent organic frameworks (COFs) one of the most chemically and structurally diverse class of materials with potential applications ranging from gas storage, molecular separation, and catalysis to energy storage and magnetism. Recently, this class of porous materials has garnered increasing interest as potential nonlinear optical (NLO) materials. Traditionally, inorganic crystals, small-molecule organic chromophores, and oligomers have been studied for their NLO response. Nevertheless, COFs offer significant advantages over existing NLO materials in terms of higher mechanical strength, thermochemical stability, and extended conjugation. Herein, we discuss crucial aspects, terminology, and measurement techniques related to NLO, followed by a critical analysis of the design principles for COFs with NLO response. Furthermore, we touch on selected potential applications of these NLO materials. Finally, future prospects and challenges of COFs as NLO materials are discussed.

Covalent Organic Frameworks as Emerging Nonlinear Optical Materials

AbstractThe vastness of organic synthetic strategies and knowledge of reticular chemistry have made covalent organic frameworks (COFs) one of the most chemically and structurally diverse class of materials with potential applications ranging from gas storage, molecular separation, and catalysis to energy storage and magnetism. Recently, this class of porous materials has garnered increasing interest as potential nonlinear optical (NLO) materials. Traditionally, inorganic crystals, small‐molecule organic chromophores, and oligomers have been studied for their NLO response. Nevertheless, COFs offer significant advantages over existing NLO materials in terms of higher mechanical strength, thermochemical stability, and extended conjugation. Herein, we discuss crucial aspects, terminology, and measurement techniques related to NLO, followed by a critical analysis of the design principles for COFs with NLO response. Furthermore, we touch on selected potential applications of these NLO materials. Finally, future prospects and challenges of COFs as NLO materials are discussed.

Synergistic Steric and Electronic Effects on the Photoredox Catalysis by a Multivariate Library of Titania Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) that display photoredox activity are attractive materials for sustainable photocatalysis. The ability to tune both their pore sizes and electronic structures based solely on the choice of the building blocks makes them amenable for systematic studies based on physical organic and reticular chemistry principles with high degrees of synthetic control. Here, we present a library of eleven isoreticular and multivariate (MTV) photoredox-active MOFs, UCFMOF-n, and UCFMTV-n-x% with a formula Ti6O9[links]3, where the links are linear oligo-p-arylene dicarboxylates with n number of p-arylene rings and x mol% of multivariate links containing electron-donating groups (EDGs). The average and local structures of UCFMOFs were elucidated from advanced powder X-ray diffraction (XRD) and total scattering tools, consisting of parallel arrangements of one-dimensional (1D) [Ti6O9(CO2)6]∞ nanowires connected through the oligo-arylene links with the topology of the edge-2-transitive rod-packed hex net. Preparation of an MTV library of UCFMOFs with varying link sizes and amine EDG functionalization enabled us to study both their steric (pore size) and electronic (highest occupied molecular orbital-lowest unoccupied molecular orbital, HOMO-LUMO, gap) effects on the substrate adsorption and photoredox transformation of benzyl alcohol. The observed relationship between the substrate uptake and reaction kinetics with the molecular traits of the links indicates that longer links, as well as increased EDG functionalization, exhibit impressive photocatalytic rates, outperforming MIL-125 by almost 20-fold. Our studies relating photocatalytic activity with pore size and electronic functionalization demonstrate how these are important parameters to consider when designing new MOF photocatalysts.

Reticular Design of Precise Linker Installation into a Zirconium Metal–Organic Framework to Reinforce Hydrolytic Stability

Reticular chemistry allows for the rational assembly of metal-organic frameworks (MOFs) with designed structures and desirable functionalities for advanced applications. However, it remains challenging to construct multi-component MOFs with unprecedented complexity and control through insertion of secondary or ternary linkers. Herein, we demonstrate that a Zr-based MOF, NU-600 with a (4,6)-connected she topology, has been judiciously selected to employ a linker installation strategy to precisely insert two linear linkers with different lengths into two crystallographically distinct pockets in a one-pot, de novo reaction. We reveal that the hydrolytic stability of these linker-inserted MOFs can be remarkably reinforced by increasing the Zr6 node connectivity, while maintaining comparable water uptake capacity and pore-filling pressure as the pristine NU-600. Furthermore, introducing hydrophilic -OH groups into the linear linker backbones to construct multivariate MOFs can effectively shift the pore-filling step to lower partial pressures. This methodology demonstrates a powerful strategy to reinforce the structural stability of other MOF frameworks by increasing the connectivity of metal nodes, capable of encouraging developments in fundamental sciences and practical applications.

Expanding Chitosan Reticular Chemistry Using Multifunctional and Thermally Stable Phosphorus-Containing Dendrimers

Chitosan is an astonishing building block that is extracted from marine crustacean waste, features randomly distributed amino and acetamido groups in its backbone, and can be handled in different forms, giving rise to an impressive diversity of functional nanomaterials. Hitherto, its reticular chemistry, although mandatory to circumvent its main drawback of instability, has been dominated by the use of glutaraldehyde. Unfortunately, the toxicity and inherent chemistry of the latter narrow further development of such cross-linked materials and constitute an impediment for their massive spreading and real implementation, especially in nanomedicine and related healthcare applications. Prompted by the well-established advantages of dendrimers, more distinctively those containing phosphorus in their skeleton, we herein explore the use of second- and third-generation phosphorus-containing dendrimers as cross-linkers to provide an extended covalent dendritic framework grown inside of the carbohydrate network. The presence of residual amine and aldehyde defects was explored to conjugate other chemicals (viologen-based ionic liquid and aminopropyltriethoxysilane) thereby adding more functional diversity to the assembled framework. We also leveraged on the film-forming ability of chitosan to shape the reticular network as flexible films. Despite the bulkiness of the used phosphorus dendrimers, the film-forming memory of chitosan was preserved, allowing successful preparation of highly functional, transparent, and flexible micrometer-thick bioplastics. The cross-linking seems to delay the half-weight degradation temperature of the plastics, with a significant increase in the char residue and a reduced heat release rate. Ternary objects (Congo red dye and gold nanoparticles) could also be entrapped within the transparent films without leaching or degradation, thereby expanding the usefulness of these transparent coatings as multifunctional sensors, flame retardants, biofoulants, etc.

Introduction to molecular engineering in MOFs: beyond reticular chemistry

Marco Taddei, Ashlee Howarth and Takashi Uemura introduce the Molecular Systems Design & Engineering themed issue on molecular engineering in MOFs: beyond reticular chemistry.

Multivariate metal-organic frameworks generated through post-synthetic modification: impact and future directions.

Reticular chemistry has proven to be invaluable over time, thanks to the structural versatility, and tailored porosity observed in structures like metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and metal-organic polyhedra (MOPs). Despite the wide array of ligands and metals available for synthesizing MOFs, they are still somewhat constrained by the reliance on de novo conditions and the focus on generating MOFs with single ligand and metal. To surpass these limitations, researchers have established strategies to generate multivariate (MTV) MOF structures incorporating more than one ligand/metal into the crystal lattice. MTV-MOFs have demonstrated enhanced properties by virtue of the additional functionalities incorporated within their structures. One approach to developing MTV-MOFs is through post-synthetic modification (PSM), where new functionalities are introduced after the initial synthesis, thereby achieving the enhanced properties of MTV-MOFs even in cases where the new functionalities are incompatible with MOF synthesis.

Reticular chemistry within three-dimensional covalent organic frameworks for multiple applications

This review summarizes the advances in rational design and synthesis of 3D COFs guided by reticular chemistry and briefly discusses recent progress in gas storage and separation, catalysis, fluorescence, batteries, conductivity, and drug delivery.

Reticular chemistry of uranyl phosphonates: synthesis, design, and beyond

The successful design strategy put reticular chemistry in uranyl phosphonate frameworks, which integrate multifunction to corresponding applications.

New reticular chemistry of pillared rare-earthkgdsupermolecular building layer frameworks with ethane-trapping property

A series of rare-earth pillar-layered MOFs based onkgdsupermolecular building layers have been successfully isolated for the first time, with ethane-selective properties benefiting ethylene purification in a one-step process.

Recent advances in the rational designing of metalloporphyrinoid-based CO2 reduction catalysts: From molecular structural tuning to the application in catalysis

Electro and photochemical [Formula: see text] reduction ([Formula: see text]R) has emerged as a contemporary research field for tackling the fossil fuel problems and construction of a modern chemical industry. For efficient [Formula: see text]R, a catalyst is needed, and Earth-abundant Fe, Co, and Ni-based metalloporphyrinoids have appeared as promising molecular catalysts for [Formula: see text]R. Several metal complexes of porphyrins, phthalocyanines, corroles, and chlorins-type porphyrinoids have been designed and tested for this purpose. The unique advantages in the judicious tuning of the porphyrinoid structures and their susceptibility towards different functionalization reactions allow an impressive scope to explore and establish a direct structure-activity relationship of metalloporphyrinoids towards [Formula: see text]R. There have been rapid advances in this field in the last few years. For the homogeneous [Formula: see text]R, the electronic and steric aspects of the porphyrinoids are fine-controlled by installing favorable functional groups at the periphery of the porphyrinoids. On the other hand, in heterogenous [Formula: see text]R, the design principle is guided by integrating metalloporphyrinoids in composite material after mixing with carbon supports, semiconductors, or adopting reticular chemistry. All the advancements further result in the testing of excellent metalloporphyrinoids in industrially feasible [Formula: see text] electrolyzers or photoelectrochemical devices. This review focuses on the recent advances in designing principles of metalloporphyrnoids catalysts in homogeneous, heterogeneous, and [Formula: see text]R reactors.

The future of metal-organic frameworks and covalent organic frameworks: rational synthesis and customized applications.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are designable and tunable functional crystalline porous materials that have been explored for applications such as catalysis, chemical sensing, water harvesting, gas storage, and separation. On the basis of reticular chemistry, the rational design and synthesis of MOFs and COFs allows us to have unprecedented control over their structural features and functionalities. Given the vast number of possible MOF and COF structures and the flexibility of modifying them, it remains challenging to navigate the infinite chemical space solely through a trial-and-error process. This Opinion Article provides a brief perspective of the current state and future prospects of MOFs and COFs. We envision that emerging technologies based on machine learning and robotics, such as high-throughput computational screening and fully automatic synthesis, can potentially address some challenges facing this field, accelerating the discovery of porous framework materials and the development of rational synthetic strategies for customized applications.

Rational design of stable functional metal-organic frameworks.

Functional porous metal-organic frameworks (MOFs) have been explored for a number of potential applications in catalysis, chemical sensing, water capture, gas storage, and separation. MOFs are among the most promising candidates to address challenges facing our society related to energy and environment, but the successful implementation of functional porous MOF materials are contingent on their stability; therefore, the rational design of stable MOFs plays an important role towards the development of functional porous MOFs. In this Focus article, we summarize progress in the rational design and synthesis of stable MOFs with controllable pores and functionalities. The implementation of reticular chemistry allows for the rational top-down design of stable porous MOFs with targeted topological networks and pore structures from the pre-selected building blocks. We highlight the reticular synthesis and applications of stable MOFs: (1) MOFs based on high valent metal ions (e.g., Al3+, Cr3+, Fe3+, Ti4+ and Zr4+) and carboxylate ligands; (2) MOFs based on low valent metal ions (e.g., Ni2+, Cu2+, and Zn2+) and azolate linkers. We envision that the synthetic strategies, including modulated synthesis and post-synthetic modification, can potentially be extended to other more complex systems like metal-phosphonate framework materials.

Impact of Ligand in Bimetallic Co, Ni-Metal-Organic Framework towards Oxygen Evolution Reaction

Emerging materials based on metal-organic frameworks (MOFs) have the potential to be used in electrocatalytic energy storage applications. Nevertheless, a large-scale feasible useage of MOFs is hampered by the low conductivity and masking of the active metal centre by the organic linker. In this study, a NiCo-based benzene tricarboxylic (BTC) electrocatalyst was successfully synthesized, and the properties were fine-tuned with 4,4′-bipyridine as a second ligand which benefits the charge transfer kinetics through non-covalent π–π interaction. This approach yields an exceptional performance towards oxygen evolution reaction (OER) at three different KOH concentrations 1, 0.5, and 0.1 M. The electrocatalyst NiCo-Bpy-BTC when tested under three different concentrations of KOH, exhibited overpotentials of 292, 343, and 407 mV to reach the 10mA cm−2 current density respectively. The obtained Tafel slope values were lower than those of Ni-Bpy-BTC, Co-Bpy-BTC, and bare NiCo-BTC respectively. Moreover, we have achieved long-term durability for up to 16 h in all KOH concentrations. Our strategy interconnects reticular chemistry and materials electrochemistry and this new approach is useful in the design of new materials for energy-related applications.

Democratizing the Assessment of Thermal Robustness of Metal-Organic Frameworks.

With the pressing need of having reliable materials for carbon dioxide capture, metal-organic frameworks (MOFs) have shown promising performance due to their flexible sign and tunable functionality by applying reticular chemistry principles. One of the main characteristics of practical MOFs is to design thermally robust candidates for sustainable functionality. Here, we introduce a comprehensive methodology for examining the thermal stability of MOFs by combining theoretical calculations and affordable experimental methods to fully describe their performance under thermal variations. We chose the prototypical MOF, HKUST-1, to assess the methodology by performing density functional theory and classical molecular dynamics simulations and validating with experiments such as in situ powder X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. HKUST-1 shows thermal robustness until a temperature of 240 °C at different atmospheric gases with a reversible breathing trend with temperature. This methodology is affordable as it uses minimal experimental testing and can be applied to any MOF materials to explore its suitability for practical applications.

Reticular Chemistry with Art: A Case Study of Olympic Rings-Inspired Metal-Organic Frameworks.

Herein, we demonstrate the successful utilization of reticular chemistry as an excellent designing strategy for the deliberate construction of a zirconium-tetracarboxylate metal-organic framework (MOF) inspired by the Olympic rings. HIAM-4017, with an unprecedented (4,8)-c underlying net topology termed jcs, was developed via insightful reconstruction of the rings and judicious design of a nonsymmetric organic linker. HIAM-4017 exhibits high porosity and excellent chemical and thermal stability. Furthermore, excited-state intramolecular proton transfer (ESIPT) was achieved in an isoreticular MOF, HIAM-4018, with a large Stokes shift of 155 nm as a result of introducing the hydroxyl group to the linker skeleton to induce OH···N interactions. Such interactions were analyzed thoroughly by employing the time-dependent density functional theory (TD-DFT). Because of their good thermal and chemical stability, and strong luminescence, nanosized HIAM-4017 and HIAM-4018 were fabricated and used for Cr2O72- detection. Both MOFs demonstrate excellent sensitivity and selectivity. This work represents a neat example of building structure- and property-specific MOFs guided by reticular chemistry.