Parent Metal-organic Frameworks Research Articles

Guest Editorial: Solar Energy Utilization

Guest Editorial: Solar Energy Utilization

A mini review on metal-organic framework-based electrode materials for capacitive deionization.

Capacitive deionization (CDI) is an electrochemical method of extracting ions from solution at potentials below electrolysis. It has various applications ranging from water remediation and desalination to heavy metal removal and selective resource recovery. A CDI device applies an electrical charge across two porous electrodes to attract and remove ions without producing waste products. It is generally considered environmentally friendly and promising for sustainability, yet ion removal efficiency still falls short of more established filtration methods. Commercially available activated carbon is typically used for CDI, and its ion adsorption capacity is low at approximately 20-30 mg g-1. Recently, much interest has been in the highly porous and well-structured family of materials known as metal-organic frameworks (MOFs). Most MOFs are poor conductors of electricity and cannot be directly used to make electrodes. A common workaround is to pyrolyze the MOF to convert its organic components to carbon while maintaining its underlying microstructure. However, most MOF-derived materials only retain partial microstructure after pyrolysis and cannot inherit the robust porosity of the parent MOFs. This review provides a systematic breakdown of structure-performance relationships between a MOF-derived material and its CDI performance based on recent works. This review also serves as a starting point for researchers interested in developing MOF-derived materials for CDI applications.

Evaluation on the performances of adsorption desalination employing functionalized metal-organic frameworks (MOFs)

• Isotherms and kinetics data for water adsorption on functionalized MOFs. • Equations of entropy flow and generation for evaluating AD performances. • Measurement of structural and thermal stabilities of functionalized MOFs. • Calculation of SDWP and PR by temperature-entropy analysis for the first time. • 5%Li-Al-Fum shows minimum entropy generation with higher SDWP. This study focuses on a comprehensive study of MOFs (metal-organic frameworks) plus water systems for adsorption desalination applications. The paper first deals with the modification of parent MOFs such as aluminium fumarate, MOF-801 (Zr) and UiO-66 (Zr) employing MOFs functionalization, alkali ion doping and impregnation of zeolites, and secondly, we focus on their characterizations for understanding both structural and thermal stabilities. Later, water adsorption on these parents and modified MOFs are investigated for a wide range of pressure (0 < P/P s < 1.0) and temperature (30 to 80 °C). Based on experimentally confirmed isotherms, kinetics and MOFs characteristics data, the performance factors such as SDWP (specific daily water production) and PR (performance ratio) are evaluated for various regeneration temperature (55 to 80 °C) and cycle time (100 to 1000 s). Furthermore, the water adsorption characteristics are applied to calculate the entropy flow and generation for each component of AD system. The SDWP is also calculated from the concepts of temperature – entropy diagram. It is found that both OH-UiO-66 (Zr) and 5%Li-Al-FumMOFs provide promising SDWP (> 34 m 3 /tonne of MOFs/day) and 5%Li-Al-Fum shows minimum entropy generation.

Design of Flexible Metal–Organic Framework-Based Superprotonic Conductors and Their Fabrication with a Polymer into Proton Exchange Membranes

In recent times, the deployment of metal–organic frameworks (MOFs) to develop efficient proton conductors has gained immense popularity in the arena of sustainable energy research due to the ease of structural and functional tunability in MOFs. In this work, we have focused on developing “flexible MOF”-based proton conductors with Fe-MIL-53-NH2 and Fe-MIL-88B-NH2 MOFs using postsynthetic modification (PSM) as the tool. Taking advantage of the porous nature of these frameworks, we have carried out PSM on the primary amine groups present on the MOFs and converted them to −NH(CH2CH2CH2SO3H) groups. The PSM increased the number of labile protons in the channels of the modified MOFs as well as the extent of H-bonded networks inside the framework. The modified Fe-MIL-53-NH2 and Fe-MIL-88B-NH2 MOFs, named hereafter as 53-S and 88B-S, respectively, showed proton conductivity of 1.298 × 10–2 and 1.687 × 10–2 S cm–1 at ∼80 °C and 98% relative humidity (RH), respectively. This reflects ∼10-fold and ∼5-fold increases in their proton conductivity than their respective parent MOFs. Since MOFs as such are difficult to make directly into flexible membranes, and these are essential for practical applications as proton conductors, we have incorporated 53-S and 88B-S as fillers into a robust imidazole-based polymer matrix, namely, OPBI [poly(4,4′-diphenylether-5,5′-bibenzimidazole)]. The resulting polymer–MOF mixed matrix membranes (MMMs) after doping with phosphoric acid (PA) performed as flexible proton exchange membranes (PEMs) above 100 °C under anhydrous conditions and were found to be much more efficient and stable than the pristine OPBI membrane (devoid of any filler loading). By optimizing the amount of filler loading in the membrane, we obtained the highest proton conductivity of 0.304 S cm–1 at 160 °C under anhydrous conditions.

Water-stable composite of HKUST-1 with its pyrolysis products for enhanced CO2 capture capacity

The composite adsorbent of HKUST-1 with its pyrolysis products has excellent water stability and CO 2 capture capacity. • Synthesis of HKUST-1 and its pyrolysis products to prepare a novel CO 2 adsorbent. • The BET and V total of HKUST-1/x increased significantly compared with pure HKUST-1. • HKUST-1/800 had the highest CO 2 capacity of 9.02 mmol·g -1 at 273 K and 1 bar. • The CO 2 /N 2 (15:85) selectivity of HKUST-1/800 was 106. • HKUST-1/800 still maintained excellent CO 2 adsorption amounts after soaking in water. Parent metal-organic framework (MOF), especially HKUST-1, is difficult to achieve both high CO 2 adsorption capacity and excellent water stability. We proposed an innovative strategy to prepare novel composites of HKUST-1/x (x, pyrolysis temperature=400, 600, 800 ℃) by the combination of parent HKUST-1 and its pyrolysis products. SEM, FT-IR and XRD characterization results verified the successful modification of the samples. The adsorption isotherm curves of N 2 and CO 2 showed that HKUST-1/800 had the highest specific surface area (1817 m 2 ·g -1 ), pore volume (0.802 cm 3 ·g -1 ) and CO 2 adsorption capacity (9.02 mmol·g -1 , at 273 K and 1 bar), which exhibited a significant enhancement effect. As well as, the CO 2 /N 2 (15:85) selectivity of HKUST-1/800 was 2.4 times higher than that of pure HKUST-1. In addition, the hydrophobicity and water stability of HKUST-1/800 were improved significantly. The water contact angle (WCA) of HKUST-1/800 reached 82.5°, 3.5 times higher than that of pure HKUST-1, and HKUST-1/800 retained most of the CO 2 adsorption capacity (5.46 and 4.31 mmol·g -1 ) after soaking in water for 1 and 5 days, respectively. However, HKUST-1 lost the majority of its adsorption capacity (retained only 0.91 and 0.74 mmol·g -1 ). The increase in the number of Cu sites and the formation of hydrophobic microenvironment on the surface were the reasons for its excellent adsorption capacity and water stability. Above of all, these hold a great potential for carbon capture applications in humid environments.

Controlling the Adsorption and Release of Ocular Drugs in Metal-Organic Frameworks: Effect of Polar Functional Groups.

A series of UiO-66 materials with different functional groups (-H, -NH2, and -NO2) have been evaluated for the adsorption and release of a common ocular drug such as brimonidine tartrate. UiO-66 samples were synthesized under solvothermal conditions and activated by solvent exchange with ethanol. Experimental results suggest that the incorporation of surface functionalities gives rise to the development of structural defects (missing linker defects) but without altering the basic topology of the UiO-66 framework. These defects improve the adsorption performance of the parent metal-organic framework (MOF), while the bulkier functionalities infer slower release kinetics, with the associated benefits for prolonged delivery of brimonidine. Among the evaluated MOFs, defective UiO-66-NO2 can be proposed as the most promising candidate due to the combination of a larger brimonidine volumetric uptake (680 mg/cm3), a prolonged delivery (period of up to 25 days), a small particle size, and a larger instability. Contrariwise, at high concentrations UiO-66-NO2 has higher toxicity toward human retinal pigment epithelium cells (ARPE-19) compared to the pure and NH2-functionalized UiO-66.

Sulfated Zirconium Metal-Organic Frameworks as Well-Defined Supports for Enhancing Organometallic Catalysis.

Understanding heterogeneous catalysts is a challenging pursuit due to surface site nonuniformity and aperiodicity in traditionally used materials. One example is sulfated metal oxides, which function as highly active catalysts and as supports for organometallic complexes. These applications are due to traits such as acidity, ability to act as a weakly coordinating ligand, and aptitude for promoting transformations via radical cation intermediates. Research is ongoing about the structural features of sulfated metal oxides that imbue the aforementioned properties, such as sulfate geometry and coordination. To better understand these materials, metal-organic frameworks (MOFs) have been targeted as structurally defined analogues. Composed of inorganic nodes and organic linkers, MOFs possess features such as high porosity and crystallinity, which make them attractive for mechanistic studies of heterogeneous catalysts. In this work, Zr6-based MOF NU-1000 is sulfated and characterized using techniques such as single crystal X-ray diffraction in addition to diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The dynamic nature of the sulfate binding motif is found to transition from monodentate, to bidentate, to tridentate depending on the degree of hydration, as supported by density functional theory (DFT) calculations. Heightened Brønsted acidity compared to the parent MOF was observed upon sulfation and probed through trimethylphosphine oxide physisorption, ammonia sorption, in situ ammonia DRIFTS, and DFT studies. With the support structure benchmarked, an organoiridium complex was chemisorbed onto the sulfated MOF node, and the efficacy of this supported catalyst was demonstrated for stoichiometric and catalytic activation of benzene-d6 and toluene with structure-activity relationships derived.

Functionalized UiO-66-NH2 by trimellitic acid for highly selective adsorption of basic blue 3 from aqueous solutions.

A novel metal-organic framework (MOF) UiO-66-TLA (UiO-66-Trimellitic Acid) was synthesized by one-pot method with trimellitic acid as modifier, which can effectively remove the basic dye Basic Blue 3 (BB3) in wastewater. Modification with carboxyl groups facilitates the adsorption of the cationic dye Basic Blue 3. The adsorption of BB3 by the modified UiO-66-TLA was significantly greater than that of its parent MOF. The adsorption capacity of the modified UiO-66-TLA for BB3 (234.23 mg g−1) was 93.2% higher than that of the original UiO-66-NH2 (121.24 mg g−1), this is closely related to the electrostatic interaction of -COOH in trimellitic acid. UiO-66-TLA was successfully synthesized as indicated by various characterization results. The adsorption kinetics conformed to the pseudo-second-order model, and the adsorption isotherm conformed to the Redlich-Peterson isotherm. This indicates that BB3 is a multi-parameter model of monolayer/multilayer arrangement on the adsorbent surface, and its rate-controlling step is chemisorption. The adsorption process was non-spontaneous and belonged to an endothermic reaction, in addition, it has great adsorption stability and regeneration The interaction of the modified UiO-66-TLA with BB3 was mainly affected by mechanisms, such as electrostatic interaction, π–π stacking as well as the abundant functional groups on UiO-66-TLA surface. These results demonstrate that UiO-66-TLA is an efficient, regenerable, water-stable material for the removal of BB3 in solution, with practical implications, suggesting its potential as a dye adsorbent.

Insights into Solid-To-Solid Transformation of MOF Amorphous Phases.

Metal-organic frameworks (MOFs) have been recently explored as crystalline solids for conversion into amorphous phases demonstrating non-specific mechanical, catalytic, and optical properties. The real-time control of such structural transformations and their outcomes still remain a challenge. Here, we use in situ high-resolution transmission electron microscopy with 0.01 s time resolution to explore non-thermal (electron induced) amorphization of a MOF single crystal, followed by transformation into an amorphous nanomaterial. By comparing a series of M-BTC (M: Fe3+, Co3+, Co2+, Ni2+, and Cu2+; BTC: 1,3,5-benzentricarboxylic acid), we demonstrate that the topology of a metal cluster of the parent MOFs determines the rate of formation and the chemistry of the resulting phases containing an intact ligand and metal or metal oxide nanoparticles. Confocal Raman and photoluminescence spectroscopies further confirm the integrity of the BTC ligand and coordination bond breaking, while high-resolution imaging with chemical and structural analysis over time allows for tracking the dynamics of solid-to-solid transformations. The revealed relationship between the initial and resulting structures and the stability of the obtained phase and its photoluminescence over time contribute to the design of new amorphous MOF-based optical nanomaterials.

Multicomponent, Functionalized HKUST-1 Analogues Assembled via Reticulation of Prefabricated Metal-Organic Polyhedral Cavities.

Metal–organic frameworks (MOFs) assembled from multiple building blocks exhibit greater chemical complexity and superior functionality in practical applications. Herein, we report a new approach based on using prefabricated cavities to design isoreticular multicomponent MOFs from a known parent MOF. We demonstrate this concept with the formation of multicomponent HKUST-1 analogues, using a prefabricated cavity that comprises a cuboctahedral Rh(II) metal–organic polyhedron functionalized with 24 carboxylic acid groups. The cavities are reticulated in three dimensions via Cu(II)-paddlewheel clusters and (functionalized) 1,3,5-benzenetricarboxylate linkers to form three- and four-component HKUST-1 analogues.

An Integrated Computational–Experimental Hierarchical Approach for the Rational Design of an IL/UiO‐66 Composite Offering Infinite CO2 Selectivity

AbstractOwing to the possibility of generating theoretically unlimited numbers of ionic liquid (IL)–metal‐organic framework (MOF) combinations, experimental studies on IL/MOF composites for gas separation applications are mostly conducted on a trial‐and‐error basis. To address this problem, an integrated computational–experimental hierarchical approach is presented for selecting the best IL‐MOF combination for a target gas separation application. For this purpose, UiO‐66 and pyrrolidinium‐based ILs are chosen as the parent MOF and IL family, respectively, and three powerful computational tools, Conductor‐like Screening Model for Realistic Solvents calculations, density functional theory calculations, and grand canonical Monte Carlo simulations, are integrated to identify the most promising IL‐UiO‐66 combination as 1‐n‐butyl‐1‐methylpyrrolidinium dicyanamide/UiO‐66, [BMPyrr][DCA]/UiO‐66. Then, this composite is synthesized, characterized in deep detail, and tested for CO2/N2, CO2/CH4, and CH4/N2 separations. Results demonstrate that [BMPyrr][DCA]/UiO‐66 offers an extraordinary gas separation performance, with practically infinite CO2 and CH4 selectivities over N2 at 15 °C and at low pressures. The integrated hierarchical approach proposed in this work paves the way for the rational design and development of novel IL/MOF composites offering exceptional performance for any desired gas separation application.

The Growth of Metal-Organic Frameworks in the Presence of Graphene Oxide: A Mini Review.

Integrated metal–organic frameworks (MOFs) with graphene oxide (GO) have aroused huge interest in recent years due to their unique properties and excellent performance compared to MOFs or GO alone. While a lot of attention has been focused on the synthesis methodologies and the performance analysis of the composite materials in recent years, the fundamental formation/crystallization mechanism(s) is (are) still not fully understood. Ascribed to the distinctive structural and functional properties of GO, the nucleation and crystallization process of MOFs could be altered/promoted, forming MOF/GO composite materials with different nanostructures. Furthermore, the MOF’s parental structure could also influence how the GO and MOF bond together. Thus, this short review attempted to provide critical and indepth discussions of recent research results with a particular focus on the factors that influence the directional growth of parent MOFs in the presence of graphene oxide. Due to the unique structure and enhanced properties, the derived MOF/GO composites have a wide range of applications including gas separation, electrochemistry, and photocatalysis. We hope this review will be of interest to researchers working on MOF design, crystal structure control (e.g., orientation), and composite materials development.

Seed-aided green synthesis of metal-organic frameworks in water

Green synthesis of metal-organic frameworks (MOFs) in water with alleviated environmental influence and reduced cost is an essential step to transfer laboratory MOFs research to industrial application. Switching from the commonly used organic solvents to pure water encounters challenges of the poor solubility of organic linkers, slow reaction kinetics, and the formation of polymorphic products. So far, a universal MOFs synthetic strategy in water system has yet to be developed. This study reports the seed-aided synthesis of eleven MOFs with diverse compositions and structures while pure water serving as solvent. The corresponding reaction temperature and time of using this new strategy were reduced compared with original synthetic approaches, while the products maintain porous structure and high crystallinity. The success of this strategy relies on the addition of parent MOFs as seeds which could promote crystallization process by skipping the time-consuming induction period and avoiding the formation of polymorphic impurities.

Histidine-engineered metal-organic frameworks with enhanced peroxidase-like activity for sensitive detection of metallothioneins

The elaborate design and fabrication of nanomaterials to mimic natural enzyme-catalyzed active sites is a promising approach to significantly improve catalytic performances, which is beneficial to the signal amplification for biosensing applications. Metal–organic frameworks (MOFs) with tailorable components, structures and well-distributed metal sites are supposed to tackle the challenges in traditional nanomaterials of vague structure and imprecise coordination. Herein, defect-engineered MOFs with histidine-functionalized active sites (His-MIL-101) has been constructed by the missing linker strategy. Bearing a histidine unit in the iron active site, the resultant His-MIL-101 can vividly mimic the natural enzyme catalytic pocket and exhibits double the peroxidase-like activity of parent MOFs. Notably, the introduction of histidine can not only increase the specific surface area for boosting the metal active site exposure but also provide an optimized electronic structure of active sites to promote the generation of active intermediate (hydroxyl radical). By virtue of the synergistic effects of metallothioneins on metal active site-blocking impact and free radicals scavenging, His-MIL-101-based colorimetric biosensing platform was constructed to accurately detect metallothioneins with a wide detection range from 20 nM to 50 μM, as well as a low detection limit of 10.49 nM. This approach paves the way for the design of advanced biomimetic nanomaterials to efficiently mimic the active center of natural enzymes and further extend the application in biosensing.

Multinuclear solid-state NMR: Unveiling the local structure of defective MOF MIL-120

Metal-organic frameworks (MOFs) are emerging materials with many current and potential applications due to their unique properties. One critical feature is that the physical and chemical properties of MOFs are tunable. One of the methods for tuning MOF properties is to introduce defects by design for desired applications. Characterization of MOF defects is important, but very challenging due to the local nature and short-range ordering. In this work, we have introduced the ordered vacancies (the defects) in the form of the coordinatively unsaturated sites (CUSs) into the framework of MOF MIL-120(Al). The creation of ordered vacancies is achieved by replacing one quarter of the BTEC (1,2,4,5-benzenetetracarboxylate) with BDC (benzene-1,4-dicarboxylate) linkers. Both parent and defective MOFs were characterized by multinuclear solid-state NMR spectroscopy. 1H MAS NMR is used to characterize the hydrogen bonding in these MOFs, whereas 13C CP MAS NMR confirms unambiguously that the BDC is incorporated into the framework. One-dimensional 27Al MAS NMR provides direct evidence of the coordinatively unsaturated Al sites (the defects). Furthermore, 27Al 3QMAS experiments at 21.1 ​T allow direct identification of one penta-coordinated and three chemically inequivalent octahedral Al sites in the defective MIL-120(Al). Two of the above-mentioned octahedral Al sites are in the domain which appears defect-free. The third octahedral Al site is near the defective site. This work clearly demonstrates the power of solid-state NMR spectroscopy for characterization of defective MOFs.

Engineering Hierarchical Architecture of Metal-Organic Frameworks for Highly Efficient Overall CO2 Photoreduction.

Previous studies on syntheses of metal-organic frameworks (MOFs) for photocatalytic CO2 reduction are mainly focused on the exquisite control over the net topology and the functionality of metal clusters/organic building blocks. This contribution demonstrates that the rational design of MOF-based photocatalyst can be further extended to the hierarchical structure at micrometer scales well beyond the conventional MOF design at the molecular level. By taking advantage of the disparity of two selective MOFs in nucleation kinetics, a hierarchical core-shell MOF@MOF structure is successfully constructed through a simple one-pot synthesis. Besides inheriting the high porosity, crystallinity, and robustness of parent MOFs, the obtained heterojunction exhibits extended photoresponse, optimized band alignment with large overpotential, and greatly enhanced photogenerated charge separation, which would be hardly realized by the merely molecular-level assembly. As a result, the challenging overall CO2 photoreduction is achieved, which generates a record high HCOOH production (146.0µmol/g/h) without using any sacrificial reagents. Moreover, the core-shell structure exhibits a more effective use of photogenerated electrons than the individual MOFs. This work shows that harnessing the hierarchical architecture of MOFs present a new and effective alternative to tuning the photocatalytic performance at a mesoscopic level.

Collaborative pore partition and pore surface fluorination within a metal–organic framework for high-performance C2H2/CO2 separation

• The C 2 H 2 /CO 2 separation for fluorinated and nonfluorinated MOFs is presented. • JXNU-12(F) exhibits significantly enhanced C 2 H 2 /CO 2 separation than that of JXNU-12. • JXNU-12(F) dispalys aprominent C 2 H 2 -captured amount in the breakthrough experiments. • Fluorination exerts a pronounced impact on C 2 H 2 uptake and C 2 H 2 /CO 2 selectivity. • The pores induced by pore partition and fluorination are optimized for trapping C 2 H 2 . Inspired by the unique properties of fluorous compounds, the deliberate replacement of H atoms with F atoms in organic linkers of metal–organic frameworks (MOFs) could be of highly interesting. Herein we rationally developed a fluorinated MOF of JXNU-12(F) derived from the parent MOF of JXNU-12 in the presence of the pore partition agent. Remarkably, H/F substitution maintains the crystal structures of MOFs but dramatically enhances the C 2 H 2 /CO 2 separation properties. The C 2 H 2 uptake of JXNU-12(F) (298 K and 1 bar) is 1.48 times higher than that of JXNU-12 even though the pore volume of JXNU-12(F) is 84% of JXNU-12. Whereas both MOFs exhibit the same CO 2 uptakes under the same conditions. The C 2 H 2 /CO 2 adsorption selectivity of JXNU-12(F) at 1 bar and 298 K is 2 times that of JXNU-12, emphasizing the importance of fluorine substitution. An excellent C 2 H 2 /CO 2 separation with a large C 2 H 2 captured amount of 4.7 mmol g −1 was achieved with JXNU-12(F), ranking among the best-performing MOFs. The significant performance enhancement in JXNU-12(F) is rationalized by the large electronegativity and polarizability of fluorine groups exposed on the pore surfaces and the well-matched pore spaces generated by pore partition for trapping C 2 H 2 , which collaboratively enhance framework-C 2 H 2 interactions as revealed by computional simulations.

Synthesis, Structure and Topology of Copper(I) Tetrazolate Framework: Facile Approach to Design Multiple Dye Adsorbent with Carbon Composites

AbstractThe development of porous tetrazolate metal‐organic frameworks (MOFs) and their carbon composites for the efficient adsorption of organic dyes is a highly exciting field for material developments as well as waste water treatment. Herein, we have introduced a copper tetrazole‐based metal organic framework, {(Cu(C2N4H3); CUT1}, synthesized via in‐situ ligand synthesis followed by [2+3] cycloaddition strategy. A set of activated carbon (AC) composites namely as CUT1@1 %AC‐Black and CUT1@5 %AC‐Black have also been prepared by loading of different proportions of activated carbon (AC) in CUT1 via sonication process. Single‐crystal X‐ray data and topological analysis results have been shown that the parent MOF (CUT1) exhibits a three‐dimensional extended structure and formed 43.62.8 ptr net topology. The phase purity and surface area of as‐synthesized MOF and AC composite have been examined through various techniques. The dye adsorption properties have been investigated for present materials by using three anionic dyes and three cationic dyes at room temperature. The results of adsorption studies demonstrated that 5 wt.% AC carbon composite is adequate for promising adsorption activity against all selected organic dyes compared to parent MOF (CUT1). A minor enhancement of surface area in the composite material exhibits the adsorption of both the cationic and anionic dyes rendering the structure and morphology remains unchanged.

PoreMatMod.jl: Julia Package for in Silico Postsynthetic Modification of Crystal Structure Models.

PoreMatMod.jl is a free, open-source, user-friendly, and documented Julia package for modifying crystal structure models of porous materials such as metal-organic frameworks (MOFs). PoreMatMod.jl functions as a find-and-replace algorithm on crystal structures by leveraging (i) Ullmann's algorithm to search for subgraphs of the crystal structure graph that are isomorphic to the graph of a query fragment and (ii) the orthogonal Procrustes algorithm to align a replacement fragment with a targeted substructure of the crystal structure for installation. The prominent application of PoreMatMod.jl is to generate libraries of hypothetical structures for virtual screenings. For example, one can install functional groups on the linkers of a parent MOF, mimicking postsynthetic modification. Other applications of PoreMatMod.jl to modify crystal structure models include introducing defects with precision and correcting artifacts of X-ray structure determination (adding missing hydrogen atoms, resolving disorder, and removing guest molecules). The find-and-replace operations implemented by PoreMatMod.jl can be applied broadly to diverse atomistic systems for various in silico structural modification tasks.

Sequence control of metals in MOF by coordination number precoding for electrocatalytic oxygen evolution

Inorganic porous materials are prevailing in energy storage, environment remediation, and catalysis; however, it is attractive to control the spatial arrangement of heterometals in these materials with atomic accuracy. Here, we report the precise positioning of metals with identical valence, coordination number, and similar size, such as Zn (II) and Co (II), to generate an alternating sequence in a multivariate (MTV) metal-organic framework (MOF), ZnCo-MTV-MOF-699, with a rare sheet secondary building unit. This is achieved by precoding their coordination number in a parent MOF, ZnCo-MOF-69C, followed by single-crystal-to-single-crystal transformation, where the entire process is monitored in situ by time-resolved small-angle X-ray scattering. Coordination number precoding of other metal pairs, Zn-Ni and Zn-Cu, in MTV-MOFs is also obtained. The sequence-coded MTV-MOF exhibits a much lower overpotential than that of the non-coded counterpart in oxygen evolution reaction, unveiling the power of metal sequence control. • Single crystals of heterometallic MOF composed of 2D sheet SBUs have been synthesized • Heterometals with similar size and valence are arranged in an alternating sequence • In situ SAXS unveils the change of metal coordination number in crystal conversion • Sequence-coded MOF exhibits a much lower overpotential than that of the non-coded one The sequence of heterometals in multivariate (MTV) metal-organic frameworks (MOFs) is like the “gene” of these porous materials, dictating their macroscopic physical properties. Currently, there are not many effective means to control such sequences. The sequence precoding method demonstrated here allows for the precise control of the spatial arrangement of heterometals in 2D sheet secondary building units (SBUs), as confirmed by both single-crystal diffraction and in situ small-angle powder X-ray scattering. The metals are arranged in a rare alternating sequence, despite their similarity in coordination environments, valence, and ionic radius. The sequence-coded ZnCo-MTV-MOF-699 exhibits an overpotential of 231 mV versus reversible hydrogen electrode (RHE) at a standard current density of 10 mA cm −2 , better than the benchmark IrO 2 , 314 mV, and rivaling most MOF-based oxygen evolution reaction (OER) catalysts. This method stands as a new way to design multivariate functional materials for electrocatalysis. Precise positioning of metals with an alternating sequence is achieved in MTV-MOF with sheet secondary building units by coordination numbers precoding and single-crystal-to-single-crystal conversion.