Open research questions in Metal-Organic Frameworks: Synthesis and Applications
52 unresolved questions extracted from the limitations and future-work sections of 436 Metal-Organic Frameworks: Synthesis and Applications papers in our library. Each links back to the study that raised it.
What the literature leaves open
5.1. Conclusion Chen et al. fundamental laboratory research in the green oxidation of sulfur-containing advances compounds and successfully addressed many inherent shortcomings of homogeneous POM catalysts, the transition from large-scale industrial application still faces multiple challenges, such as insufficient synthetic controllability, ambiguous structure- property relationships, limited mechanistic understanding, and poor engineering compatibility. Future studies may focus on the following five key dimensions to conduct systematic and forward-looking exploration and breakthroughs. to (i) Atomic-level precision innovation and green scalable in- upgrades in synthetic methodologies. Current mainstream situ methods, such as impregnation, ion exchange, and simple encapsulation strategies, commonly suffer from uneven POM loading, random distribution of active sites, weak host- guest interactions, and potential structural damage to POMs. via One of the core future research directions lies in developing atomic-level precise construction techniques, for instance, coordination-directed self-assembly, site-specific covalent bonding, or post-synthetic modification strategies, to precisely anchor POM units with specific composition and structure at predetermined nodes or within the channels of porous frameworks. This enables monodisperse, high-density, and oriented arrangement of active centers. Meanwhile, there is an urgent need to explore green, low-cost, and scalable synthesis processes, including mechanochemical ball milling, microwave-assisted continuous-flow synthesis, and scaled-up improvements of hydro-/solvo- thermal methods. These advancements will lay a practical foundation for industrial applications such as deep fuel desulfurization and industrial wastewater treatment. This article systematically reviews and comprehensively summarizes the latest research advances and development trends in composite catalysts constructed by encapsulating POMs within emerging porous framework materials, namely MOFs and COFs, for the green oxidative transformation of sulfur-containing compounds. Addressing long-standing scientific challenges in practical applications of homogeneous POM catalysts, including tendencies toward agglomeration and leaching, insufficient exposure of active sites, and lack of substrate selectivity regulation, POM@MOFs and POM@COFs composites offer effective solutions through precise design and synergistic modulation of host-guest architectures. This review focuses on three representative application scenarios: selective oxidation of active sulfides in biomedicine, deep oxidative desulfurization of fuels in environmental and energy fields, and degradation of chemical warfare agent simulants in public safety. Synthesizing existing research findings, the superior catalytic performance of POM@MOFs and POM@COFs systems compared to individual components can be attributed to three key mechanisms.
Synergistic catalysis in POM@MOF and POM@COF composites: Emerging platforms for catalytic oxidation of sulfur-containing compounds · 2026 · DOIWhile these frameworks exhibit excellent performance in controlled, mono-pollutant laboratory settings, their competitive adsorption efficiency in complex matrixes—such as agricultural runoff containing co-existing ions, dissolved organic matter (DOM), and mixed pesticides—remains to be fully elucidated.
Synthesis of nano-Cu–Zn–MOF based on metallic waste with different carboxylic content for carbofuran residues uptake from wastewater · 2026 · DOIABSTRACT Despite the promising microenvrionments of deep eutectic solvents (DESs), including their charge‐rich nature, tunable polarity, and microviscosity, the role of neat DESs as photonic media has remained largely underexplored, often relying on the addition of ex situ‐synthesized luminophores to produce photoluminescence (PL).
In Situ Confinement of 0D Halometallates Within Deep Eutectic Solvents: From Systematic Screening to Metal‐Tunable Luminescence for Anti‐Counterfeiting Eutectogels · 2026 · DOIHowever, further work is needed to assess long- term durability, thermal integration options (e. The integration of degradation models into the optimisation framework could be explored in future work, as it may help capture efficiency decay more explicitly and provide a more comprehensive evaluation of its impact on system performance and costs.
Multi-Objective Optimization of a Power-to-Power System with Hydrogen Storage in Solid Materials at Room Temperature · 2026 · DOIThis study developed a Python based high-throughput extraction method that systematically acquired MOF void information (void count, volume, electron count), SAV, and adsorbate molecule information. It provides a more refined and reliable technical method for MOF research oriented toward adsorption-separation applications. Building on our work, future efforts will focus on establishing standard- ized data formats tailored for large language models, with explicit distinctions between chemical entities (e.g., “oxy- gen atoms” versus “oxygen molecules”), to enable high- quality machine learning training datasets. Subsequently, the extracted void characteristics will be integrated with molecular simulation techniques to construct predictive models for adsorption-separation performance. We feel that the author’s level of crystal solution and refinement or accu- racy of editing and supplementing the CIF are very impor- tant for us to extract guest molecules or information related to void. In addition, the accuracy of the descriptions in the CIF keyword indices such as _platon_squeeze_details and _ refine_special_details is very important. We hope research- ers can establish a standardized format for the descriptions in the CIF keyword indices such as _platon_squeeze_details and _refine_special_details. These insights will further guide the development of specialized tools for designing MOFs optimized for separation applications.
Python-based high-throughput extraction of void information, solvent accessible volume and adsorbate molecules from MOF for adsorption-separation applications · 2026 · DOIThe capillary column pretreatment strategy was shown to significantly enhance MOF loading, but the optimization of amino group functionalization parameters for different MOF types remains unexplored.
Solvent Polarity Matching for the Fabrication of Evenly Distributed Metal-Organic Framework Stationary Phases · 2026 · DOIThe study focuses on a single MOF material (MIL-125-NH2); generalization of the polarity matching approach to other MOF structures requires investigation.
Solvent Polarity Matching for the Fabrication of Evenly Distributed Metal-Organic Framework Stationary Phases · 2026 · DOIIn this perspective, we have summarized and analyzed the very common and interesting phenomenon of exibility in HOFs. We believe that exibility refers to the ability or range of deformability of the overall or local structure, i.e., the ability to undergo structural changes or deformations under certain stimuli without losing (or restoring) its crystallinity or function. This exibility allows HOFs to be adapted to different environments and applications. We should note that the exibility of HOFs differs notably from that of MOFs and COFs. First, the exibility of HOFs mainly comes from the exibility and reversibility of H-bonding. H-bonding is important for HOFs' exible behavior, and they can be distorted, broken, and reformed in response to external stimuli, which is a unique property of HOFs. MOFs, on the other hand, are typically exible due to their metal–organic coordination bonds between metal ions and organic ligands, which can undergo stretching or rotation to some extent, making MOFs exible to a limited degree. COFs are composed of organic molecules connected by covalent bonds that can be bent or twisted under external stresses, allowing them some deformability. The distinctive features of exible HOFs endow them with some special 9886 | Chem. Sci., 2024, 15, 9874–9892 © 2024 The Author(s). Published by the Royal Society of Chemistry Open Access Article. Published on 21 May 2024. Downloaded on 6/14/2026 7:44:20 AM.
111 X. L. Wang, L. F. Liang, S. Dou and X. M. Zhang, Two-in-one tecton strategy to construct single crystalline hydrogenbonded organic framework with high proton conductivity above 100 °C, Sci. China: Chem., 2023, 66, 2563–2568. 112 S. Chen, Y. Ju, H. Zhang, Y. Zou, S. Lin, Y. Li, S. Wang, E. Ma, W. Deng, S. Xiang, B. Chen and Z. Zhang, Photo Responsive Electron and Proton Conductivity within a Hydrogen-Bonded Organic Framework, Angew. Chem., Int. Ed., 2023, 62, e202308418. 113 Y. Wang, M. Zhang, Q. Yang, J. Yin, D. Liu, Y. Shang, Z. Kang, R. Wang, D. Sun and J. Jiang, Single-crystal-tosingle-crystal transformation and proton conductivity of three hydrogen-bonded organic frameworks, Chem. Commun., 2020, 56, 15529–15532. 114 A. Karmakar, R. Illathvalappil, B. Anothumakkool, A. Sen, P. Samanta, A. V. Desai, S. Kurungot and S. K. Ghosh, Hydrogen-Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton-Conducting Materials, Angew. Chem., Int. Ed., 2016, 55, 10667–10671. 115 M. Yoon, K. Suh, H. Kim, Y. Kim, N. Selvapalam and K. Kim, High and highly anisotropic proton conductivity in organic molecular porous materials, Angew. Chem., Int. Ed., 2011, 50, 7870–7873. 116 S. C. Pal, D. Mukherjee, R. Sahoo, S. Mondal and M. C.
detection of nitrobenzene in water, J. Mater. Chem. A, 2023, 11, 4672–4678. 64 X. Song, Y. Wang, C. Wang, X. Gao, Y. Zhou, B. Chen and P. Li, Self-Healing Hydrogen-Bonded Organic Frameworks for Low-Concentration Ammonia Capture, J. Am. Chem. Soc., 2024, 146, 627–634. 65 X. Y. Gao, Y. L. Li, T. F. Liu, X. S. Huang and R. Cao, Singleof organic crystal-to-single-crystal tetrathiafulvalene-based frameworks, CrystEngComm, 2021, 23, 4743–4747.
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Fig. 19 (left) Schematic representation of the structure and topology of PFC-71, PFC72-Co, and PFC-73-Ni/Cu/Zn; (right) the interlayer porphyrin center-to-center distance of PFC-71, PFC72-Co, and PFC-73-Cu.61 coupled electron-proton transfer. This work demonstrated that by rationally designing exible HOFs, the coupling of proton- electron transfer can be realized, resulting in controllable pho- toresponsive electronic and proton conductivity. 3.6 Other applications Further research on exible HOFs remains ongoing, and their applications involve many areas that will not be detailed here, such as catalysis,61,117–122 chiral separation,123,124 etc. CO2 In 2022, Liu et al. reported the synthesis and characterization of porphyrin-based HOFs (PFC-71, PFC-72, and PFC-73) for reduction.61 photocatalytic [5,10,15,20-tetrakis(4- carboxyphenyl)porphyrin] (TCPP) is applied to synthesize these HOFs with different metalized porphyrin centers. In the case of PFC-71, the porphyrin center is not metalized, whereas, in PFC- 72, PFC-73-Ni, PFC-73-Cu, and PFC-73-Zn, the porphyrin center is metalized with different metal ions (Co, Ni, Cu, and Zn, respectively). This metallization of the porphyrin center leads to a larger electronegativity difference on the macrocycle backbone, causing increased polarizability and electron cloud distortion, resulting in the formation of stronger offset p–p interactions between adjacent interlamellar porphyrins. PFC-72 and PFC-73 exhibit higher stability compared to PFC-71. The undulated geometry of the metalized layers, along with the deeper interlayer penetrations and orientation of benzene rings orthogonal to the layer, increases the geometrical barrier for sliding and contrib- utes to the higher stability of PFC-72 and PFC-73 (Fig. 19). The authors investigate the metallization process of the HOFs and its effect on the photocatalytic activity, demonstrating the potential of these HOFs as photocatalysts for CO2 reduction. 3.7 Future directions for exible HOFs' applications Over the last decade, research on exible HOFs has demon- In-depth strated great potential for diverse applications. research into the structure–function relationship has greatly improved the response of exible HOFs to a broader range of stimuli, particularly in biomedical applications. In recent years, there has been a lot of interest in the development of HOF membranes, and exible HOFs have the potential to expand the range of applications in this eld even further.125 In addition, researchers are improving the synthesis and processing tech- nologies of exible HOFs in order to enable further application in industry. Overall, research in the future should concentrate on utilizing the unique features of exible HOFs to provide inventive solutions for a variety of practical applications.
Fig. 15 (a) Assembling of PTTCN molecules (left) to a 2D H-bonded framework with pores (middle), and intermolecular stacking in a 2 × 2 × 2 cell (right); (b) PXRD patterns; (c) schematic representation of the separation for benzene/cyclohexane.93 free crystal under heating. This nonporous crystal could selectively reabsorb benzene from the benzene/cyclohexane mixture, allowing for the recovery of the original framework. The purity of the reabsorbed benzene reached approximately 96.5%. This work addressed the challenge of separating benzene and cyclohexane by designing a exible luminescent HOF with selective adsorption and release properties. 3.3 Sensing HOFs have demonstrated signicant promise in the elds of multiple stimulus-response and intelligent optics because of their modular building units and exible frameworks. As a multifunctional luminescent framework material with both luminescent and porosity properties, it has a broad application prospect in the eld of sensing.63,68,72,94–102 A novel triaryl formamidine salt containing two isomers (BA- C and BA-N) was reported by Lin et al.68 These two isomers can be recrystallized in different solvents to form two different HOFs, and it was found that the removal of acetone from the lattice of BA-C by grinding or heating could lead to the conversion of BA-C to BA-N, and in turn, exposing to acetone vapor or cooling at 77 K could lead to the conversion of BA-N to BA-C, thus realizing the reversibility of the conversion of BA-N and BA-C, and showing the exibility of these HOFs (Fig. 16). The exible behavior of this anionic HOF enables dynamic switching of multiple luminescence behaviors, including prompt uorescence, TADF, and phosphorescence. As a result, this HOF can be used for highly sensitive and specic sensing of acetone with an ultra-low detection limit of 66.74 ppm. There are many similar examples of utilizing the exible behavior of HOFs to achieve ne-tuning of optical properties, such as the previously mentioned 8PZ, where so ethyl-ester chains bring adaptability to different guest molecules, and endow it with programmable temperature-dependent luminescence behaviors.72 In another case, Cong et al. reported a novel polycatenated HOF MEP-HOF, which is composed of uorenylidene-aza[16]cyclophane (FLAC).63 This HOF exhibits dynamic reversible transformation in crystallinity during guest removal/adsorption and also exhibits sensitive detection of nitrobenzene. In 2021, Xue et al. investigated the inuence of guest molecules on the photoluminescence and force-stimuli Fig.
shows that neither C2H4 nor C2H6 molecules can diffuse into HOF-FJU-1 without considering the exibility of the framework, but the distribution of C2H4 in the pore is clearly observed by single crystal X-ray diffraction, which fully demonstrates the key role of exibility in this adsorption process. However, in another study, instead of showing the same exibility towards smaller gas molecules (C2H2 and CO2), HOF-FJU-1 achieves the high sieving effect of C2H2/CO2.54 Therefore, such an interesting robust-exible HOF exhibited completely different adsorption behaviors with different adsorption guests, showing the remarkable versatility of exible HOFs. Very recently, Li et al. reported a carboxyl-based HOF, ZJU- HOF-8, with exible-robust porosity for natural gas purication.55 ZJU-HOF-8 is constructed from 2,3,5,6-tetrakis(4- carboxyphenyl)-pyrazine (H4TCPZ) organic units via intermolecular C–H/N, C–H/O and C–H/p interactions (Fig. 13a). ZJU-HOF-8 exhibits a unique four-fold interpenetrated subnetwork. Gas sorption and X-ray diffraction studies conrm that the activated ZJU-HOF-8a exhibits a signicant structural contraction, showing selective pore-pocket opening by certain gas molecules. This selective opening leads to higher uptakes and enhanced selectivities for C3H8 and n-C4H10 over C2H6 and CH4, highlighting the potential for designing exible-robust HOFs for improved gas separation (Fig. 13b–d). The potential application of exible HOFs in gas adsorption/ separation is actually more widespread. The renewability of Fig. 12 Schematic illustration of the dihedral angles of the pillar ring changes from 90° to 157° in Cage-6-COOH based structures.73 low.52 In addition, with the increase in temperature, the adsorption capacity for C2H6 will further decrease. Breakthrough experiments conrmed the high selectivity of HOF-FJU- 1 for C2H4 with a purity of 99.1% at 333 K. It is worth mentioning that HOF-FJU-1 exhibits stability under various harsh conditions and can be easily processed into different forms for gas separation. Interestingly, theoretical simulation Fig. 13 (a) Single-crystal structure of ZJU-HOF-8 and the structural transformation with framework contraction upon activation; (b) N2 adsorption of ZJU-HOF-8a at 77 K; (c) different gas adsorption at 296 K; (d) IAST selectivities of ZJU-HOF-8a at 296 K.55 9882 | Chem. Sci., 2024, 15, 9874–9892 © 2024 The Author(s). Published by the Royal Society of Chemistry Open Access Article. Published on 21 May 2024. Downloaded on 6/14/2026 7:44:20 AM.
stronger intermolecular interactions still maintain the stability of HOF-FJU-2, allowing this exible HOF to exhibit related properties while maintaining crystallinity. 2.4 Local dynamic behavior The concept of local dynamics highlights the local motions throughout the entire framework in contrast to the behavior of global dynamics. It has been well established that modifying dangling groups on organic ligands in MOFs can lead to exible behavior, even though the framework may not exhibit signi- cant exibility. The dangling groups can be small groups or complex interlocking supramolecular structures. Similarly, in HOFs, local exibility in the organic units can bring about signicant dynamic behavior, and this effect can either affect the properties or bring about a structural change. In addition, the rotation of the covalent bonds in the organic unit also brings about exibility and results in structural diversity.71–73 In 2023, Chi et al. reported a exible HOF, 8PZ, with local dynamics for adaptive guest accommodation through incorporating so ethyl-ester chains.72 8PZ was developed from a exible building block tetraethyl 40,4000,400000,40000000(ethene- 1,1,2,2-tetrayl)tetrakis([1,10-biphenyl]-4-carboxylate) (TPE- 4PZ), which includes four identical so ethyl-ester chains. 8PZ has been conrmed to have signicant local dynamics in response to solvents and temperature changes, especially the in-plane and out-of-plane motions of terminal carbon atoms, leading to an effective approach to regulating the pore sizes. In 2023, Little et al. reported a exible oxygen-bridged prismatic organic cage molecule, Cage-6-COOH, which has three pillars that exhibit rotational motion like a hinge in the solid state (Fig. 12).73 This organic building unit can form a series of exible HOFs by crystallizing in different solvents. CageHOF- 2a was crystallized from the THF/CH3CN solution, and each Cage-6-COOH molecule was connected to six neighboring Cage-6-COOH molecules via H-bonds between directional carboxylic acid dimers with distances of 2.58–2.59 Å. Although CageHOF-2a shows an acs topology, it is nonporous. Another CageHOF-2b was crystallized from ethanol with similar Hthe H-bond bonding patterns. However, building units are not all planar, and the aromatic pillars have profoundly different orientations. CageHOF-2b exhibited −1. good thermal stability and a BET surface area of 458 m2 g Furthermore, another ve HOFs are found with different dihedral angles between the pillars varying from 90° to 157°. The exibility of Cage-6-COOH allows this molecule to rapidly transform from a low-crystallinity solid into CageHOF-2a and CageHOF-2b under mild conditions simply by using acetonitrile or ethanol vapor, respectively. This work highlights the potential of exible organic cage hinges in the design and synthesis of exible HOFs with tunable properties. in CageHOF-2b, 3. Diverse applications for flexible HOFs Flexible HOFs stand out because of their inherent exibility, offering a wide range of potential applications. Although still Fig. 8 (a) Crystal structures of FDU-HOF-3; (b) schematic illustration of the self-healing effect of FDU-HOF-3 before and after NH3 capture.64 Fig. 9 (a) The structure of H6NBDA; (b and c) representation of the reorganization of H-bond dimers upon heating; (d) scheme of H6NBDA and the six-connected node; (e and f) the transformation of layered frameworks before and after heating.67 activation of HOF-FJU-2 will result in a single-crystal-to-singlecrystal (SCSC) transformation to a closed framework HOF-FJU- 2a. However, when soaked in acetone or exposed to acetone vapor, the yellow HOF-FJU-2a crystals can be facilely transformed back into the white porous HOF-FJU-2, exhibiting exibility in structure. Unlike HOF-FJU-1, the H-bonds formed between the CTBA molecules are not in pairs like in HOF-FJU-1, thus further increasing the local exibility and leading to structural transformation during the activation process. However, the overall 9880 | Chem. Sci., 2024, 15, 9874–9892 © 2024 The Author(s). Published by the Royal Society of Chemistry Open Access Article. Published on 21 May 2024. Downloaded on 6/14/2026 7:44:20 AM.
Layer network sliding. The exible behavior of 2D HOFs has also been observed in single-crystal structures. In 2022, our group reported an adaptive HOF, HOF-29, based on 4,40,400,4000-(porphyrin-5,10,15,20-tetrayl)tetrabenzonitrile (PTTBN).57 Each PTTBN unit is connected with four adjacent units via four pairs of intermolecular C–H/NC H-bonds, resulting in a 2D sql net. Different layers were packed in an AA stacking pattern through multiple H-bonding and p–p stacking interactions (Fig. 7a and b). HOF-29 exhibited a singlecrystal-to-single-crystal transformation from the as-synthesized AA stacking phase to another AB stacking phase aer adsorbing pX molecules by sliding the 2D layers and the local distortion of the ligand (Fig. 7c and d) realized the exclusive recognition of pX over mX, oX and EB. In some other studies, the exibility of 2D HOFs has already been applied in the eld of gas separation.56,58 In 2023, Zhang et al. reported a CO2-selective HOF-FJU-88 from 2,4,6- tri(1Hpyrazol-4-yl)pyridine (PYTPZ) building units.58 HOF-FJU- 88 consists of a 2D H-bonded layer formed from PYTPZ molecules. Each layer is further connected by p–p interactions between pyridine and pyrazole groups. During the activation process, PXRD indicates a partial loss of crystallinity due to the sliding of the 2D layers. The CO2 adsorption isotherm also exhibits a signicant gate-opening effect, demonstrating the dynamic framework nature of HOF-FJU-88. 2.3 H-bond breaking/reconstruction The reversibility of the H-bonds offers HOFs a unique type of exibility; that is, HOFs are able to return to their initial states if the structures collapse following a stimulus response, which includes physical stimuli (pressure, temperature, guest molecules, etc.) and chemical stimuli (acid, base, corrosive gases, etc.).59–69 Or, sometimes, the H-bonding patterns will just be reorganized without losing the framework crystallinity, thus the leading to a structural ethanol-bridged carboxyl dimers in HOF-30 reported by Wang et al. have exhibited reversible structural transformations with the removal of ethanol during the activation process or soaking in the solvent again.69 transformation. For example, In 2024, Li et al. reported a microporous HOF, FDU-HOF-3, for ammonia (NH3) capture. This HOF is developed from 3,30,3000,30000–(pyrene-1,3,6,8-tetrayl)tetrabenzoic acid (H4PTTB) organic units.64 In the structure, each H4PTTB building block was connected to four adjacent units via intermolecular Hbonds, along with intermolecular p–p stacking interactions, forming a three-dimensional (3D) network with sql topology (Fig. 8a). Interestingly, FDU-HOF-3 will lose its crystallinity aer NH3 adsorption. However, aer regeneration by heating and degassing, the regenerated HOFs return to the crystalline phase again.
Flexible HOFs have some obvious advantages: (1) more accessible exible behaviors. Generally, the bonding energy of −1, much lower than the coordination H-bonds is 10–40 kJ mol −1) and the covalent bonds in bonds in MOFs (90–350 kJ mol −1), making it easier for HOFs to exhibit COFs (300–600 kJ mol a certain degree of structural exibility and diversity;13 (2) better reproducibility. The reversibility of H-bonds allows us to reconnect broken H-bonding units under certain conditions, enabling the original HOFs to recover and regenerate; (3) compared to MOFs, HOFs lack metal ions (or have a lower proportion of metal ions), resulting in lower density; however they exhibit higher structural diversity than COFs, combining the different advantages of both. In this perspective, we aim to provide a unique viewpoint on discussing exible HOFs. Rather than offering a comprehensive overview of all exible HOFs, we will focus on discussing the exible behaviors of some representative exible HOFs (Table 1) and their unique applications. Additionally, we will highlight the differences between exible HOFs and other porous materials such as MOFs and COFs. 2. Different types of flexible behaviors The exibility of HOFs derives from the organic motifs as well as the weak bond strength and reversibility of the H-bond. We have so far obtained a lot of exible HOFs, although in many cases, the fragility of the crystals makes it challenging to identify the structural changes where the exible behavior occurs. Generally speaking, during the synthesis or in response to external stimuli, HOFs display four primary exible features: pore size/shape changes, interpenetration/stacking manner, H-bond breaking/ reconstruction, and local dynamic behavior (Fig. 3).
Cite this: Chem. Sci., 2024, 15, 9874 All publication charges for this article have been paid for by the Royal Society of Chemistry Received 20th April 2024 Accepted 20th May 2024 DOI: 10.1039/d4sc02628d Flexible hydrogen-bonded organic frameworks (HOFs): opportunities…
Author contributions N.S.P.V., J.L.O. and J.A.R. writing and conceptualization. R.A.P. writing, conceptualization, and organization. M.T.H. writing, conceptualization, and organization I.A.I. validated the discussion, and revised the paper. All authors contributed to reviewing and enhancing the manuscript.
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extraordinary dynamic properties from which biological function is derived144,145. Insight garnered from this transformative technology far exceeds traditional crystallographic or NMR based techniques, confirming that even within well-established fields opportunity remains to avail deeper understanding from emerging technologies. We posit that while the underlying dynamic processes in MOFs are challenging experimental subjects today, their effects should not evade our imagination. Based on the evidence available already, the role of dynamic metal-linker interactions cannot be overestimated in any attempt to conceptualise or engineer defectivity. Much has been reaped from the fertile chemical landscape that MOFs present. Increasingly, advancement has stemmed from embracing - and exploiting - the imperfections and dynamic properties of the crystalline lattice. The ascendency of glass MOFs is the ultimate manifestation of this transformation74,75,100. While the popular description of MOFs emphasises crystalline order and reticular synthesis; it is increasingly evident that imperfections grant access to new layers of chemical complexity and extraordinary opportunity.
Fig. 4 | Defect-free MOFs. a Defect-free UiO membranes are synthesised from fumaric acid, BDC or BDC-OH linkers to form a family of supported membranes with precisely regulated pore sizes. b The H2/CO2 selectivity UiO membranes is dependent on the pore size determined by linker choice and strongly degraded by increased defectivity. c HRTEM image of UiO-fumarate membrane provides evi- dence for a near ideal lattice. Figure elements adapted with permission from ref. 58. Copyright 2023 Springer Nature. d The structure of HKUST-1 is composed of CuII paddlewheel nodes bridged by BTC linkers. A known defect involves reduction of one CuII centre and loss of a single carboxylate linker. Defective HKUST-1 SURMOF samples exhibit a blue colour while high quality thin films are colourless. Figure elements adapted with permission from ref. 15. Copyright 2017 American Chemical Society. specific experiments, specialist instrumentation and data analysis required. Our understanding of defectivity (among many other aspects of MOF chemistry) will remain incomplete until the underlying local dynamics are resolved. The application of experimental and computational expertise to this end must therefore be prioritised. Our intention in raising these points is not to dissuade efforts to minimise defectivity or indeed, engineer it. Rather, we argue that these efforts are central to maximising the utility of MOFs in wide-ranging applications. Yet the transformative potential and ubiquity of dynamic bonding demands that more scrutiny be placed on the long-term stability of defect landscapes. Perhaps what is needed most is an interlaboratory study that assesses both defect reproducibility and stability in MOFs, focusing on the effects of routine processing on defect extent, type and distribution.
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