Ammonia-Assisted Chemical Vapor Deposition Growth of Two-Dimensional Conjugated Coordination Polymer Thin Films

As emerging electroactive materials, the controlled synthesis of highly ordered two-dimensional (2D) conjugated coordination polymer (c-CP) films ensuring the long-range π-electron delocalization is essential for advancing high-performance (opto-)electronics. Here, we demonstrate the growth of highly crystalline 2D c-CP thin films on inert substrates by chemical vapor deposition with the assistance of ammonia (NH3) for the first time, leveraging its deprotonation effect on ligands and competing effect as additional coordinating species. The resulting Fe-HHB (HHB = hexahydroxybenzene) films exhibit large-area uniformity and a 2 order-of-magnitude increase in crystal grain size, which translates into significant improvements in electrical conductivity (from 0.002 to 3 S/cm), charge mobility, elastic modulus, and hardness. To verify the generality of this NH3-assisted synthesis, the contrast Cu-HHB and Cu-BHT (BHT = hexathiolbenzene) 2D c-CP thin films are also prepared and deliver significantly improved electrical conductivities from 51 to 113 and from 595 to 905 S/cm, respectively. The greatly improved crystallinity, combined with the high compatibility of the developed synthetic strategy with current device integration technologies, paves the way for developing c-CP-based electronics.

Substituent Modulation of Contorted Hexa-peri-benzocoronene-Based Conjugated Metal-Organic Frameworks for High-Performance Capacitor

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) exhibiting graphite-like van der Waals stacked layers have been recognized as a new type of crystalline conductive materials and have shown rapid progress in the last decade. However, the purposive design and modulation of their conductive properties and related application performance remains a challenge. Herein, we present a new type of 2D c-MOFs with contorted conformation and substituent-modulated structures for highperformance of the capacitor. Octahydroxy-hexa-peri-benzocoronene (HBCOH) with a contorted graphene nanosheet core is designed and synthesized as the ligand. The F-substituted 2D c-MOF FHBCOH-Cu demonstrates superior crystallinity and conductive properties exhibiting a record-breaking specific capacitance of 943 F g-1 at a rate of 0.5 A g-1. The improved crystallinity, enhanced conductivity, and pore environment control enabled by halogen substitution, combined with the contorted conformation synergistically accomplish high performance of 2D c-MOFs as electrode materials in supercapacitors. This study introduces a novel molecular design strategy for the construction of 2D c-MOFs-based high-performance energy storage materials.

Conductance Reinforced Relaxation Attenuation with Strong Metal-N Coordination in Multivariate π-Conjugated MOFs for Integrated Radar-Infrared Camouflage

π-conjugated metal-organic frameworks (MOFs) have emerged as promising candidates for electromagnetic wave (EMW) absorption, owning to their high conductivity and versatile structural tunability. Nevertheless, the effective control over their dielectric properties is a challenge. Herein, the charge carrier migration in π-conjugated MOFs is harnessed to significantly amplify the electromagnetic response, where the strengthened atom coordination can activate a distinctive conductance-reinforced attenuation mechanism. This results in finely calibrated EMW absorption characteristics, including a wide effective absorption bandwidth of 6.0 GHz at mere 2 mm, a minimum reflection loss of -46.7 dB at 3.5 mm, and a substantial reduction in radar cross-section (RCS) up to -23.3 dBm2. Furthermore, the seamless integration of the π-conjugated MOF hybrids within ultraviolet (UV)-curable 3D printing technology has enabled the fabrication of a stealth-enabled drone propeller prototype, which exhibits a remarkably low infrared emissivity of 0.205. Additionally, when the propeller device is subjected to a 100 °C heating platform for 30 min, its surface temperature remains below 50 °C, demonstrating exceptional thermal management and stability under elevated temperature conditions. This work underscores the immense potential of these cutting-edge absorbers to shape the future of advanced military stealth technologies.

Catalysis-Assisted Synthesis of Two-Dimensional Conductive Metal-Organic Framework Films with Controllable Orientation

The facile preparation of two-dimensional (2D) conductive metal-organic framework (MOF) films with controllable orientation and thickness greatly facilitates the further structure-property investigation and performance optimization in their applications. Here, we report a catalysis-assisted synthesis strategy to the rapid production of oriented films of catechol-based (Cu3(HHTP)2, Zn3(HHTP)2, and Cu2TBA) and diamine-based (Ni3(HITP)2) 2D conductive MOFs with thicknesses adjustable from tens of nanometers to several micrometers. Relying on the utilization of a 0.3 nm Pt layer, which can be conveniently predecorated on a substrate surface via evaporating deposition or sputtering, as a catalyst for the aerobic oxidation of the redox-active ligands to trigger the formation of 2D conductive MOFs, this strategy is compatible with a majority of commonly used substrates and capable of producing patterned films with feature sizes ranging from micrometers to centimeters. Investigation on the growth kinetics of Cu3(HHTP)2 indicates that the preferential growth along the c-axis or in the ab-basal plane of its crystallites can be flexibly tuned by the formation reaction kinetics to guide the evolution of films with the face-on or edge-on orientation. The chemiresistive device incorporating the face-on Cu3(HHTP)2 film presents a high response (197%) and a fast respond speed (27 s) toward NH3 (30 ppm) at room temperature, which are superior not only to its edge-on counterpart (90% and 69 s, correspondingly) but also to other reported Cu3(HHTP)2-based sensors.

Two-Dimensional Conductive Metal-Organic Frameworks: Promising Materials for Advanced Energy Storage

With the rapid development of science and technology and for a sustainable future, the main energy resources in the world are transitioning from fossil fuels to renewable electricity which is conceived to play a predominant role in the future. Therefore, it is essential to develop high-performance energy-storage devices such as supercapacitors and rechargeable batteries, and even though they are commercialized, intense research efforts are still devoted to further improving the device performance, e. g. energy density, safety, durability, and charging rate. Therefore, exploring new advanced materials for better devices is a promising approach. Recently, the emerging two-dimensional conductive metal-organic frameworks (2D c-MOFs) with their inherent electrical conductivities and porosity, rich redox active sites, and tailor-made architectures and functions have attracted considerable attention among the energy-storage community. The initial research results revealed that 2D c-MOFs are promising electrode materials for advanced energy storage.

Bispidine-Based Copper(II) Coordination Polymers with Remarkable Dynamic Properties, Selective Volatile Organic Compounds Adsorption, and Exchange Capabilities

This study presents novel bispidine-based Cu(II) coordination polymers (CPs) with remarkable dynamic properties, volatile organic compounds (VOCs) exchange, and selective adsorption capabilities. The coordination requirements of Cu(II) enable, as demonstrated by SC-XRD and Powder X-ray diffraction (P-XRD), the formation of either 1D ribbon-like (1-TCMSC and 1-H2OSC) or 2D (1-MeCNSC) extended frameworks depending on the ability of the trapped solvents to interact as hydrogen bond (HB) donor with the metal's counterion. Hirshfeld Surface (HS) analysis and in situ VT SC- and P-XRD experiments reveal different interchain interactions in 1D vs 2D CPs. Solvent exchange experiments on both single crystals (SCs) and microcrystalline samples, set up to evaluate differences in the CPs' dynamic nature, confirm the drastic effect of CP dimensionality. Additionally, an amorphous desolvated phase 1-AmorphPwd was tested for VOC adsorption and demonstrated to display affinity for acetonitrile and nitromethane, with high selectivity for the latter, but also to have the ability to trap aromatic VOCs, capturing up to ca. 2 mmol/g of solvent. The adsorption experiments, conducted at r.t., 1 atm, and no prior activation, underscore the potential of these materials for environmental and industrial applications. This work emphasizes the unique dynamic and selective behavior of bispidine-based CPs and provides a foundation for their scalability and practical implementation in VOCs capture technologies.

Unveiling high-mobility hot carriers in a two-dimensional conjugated coordination polymer

Hot carriers, inheriting excess kinetic energy from high-energy photons, drive numerous optoelectronic applications reliant on non-equilibrium transport processes. Although extensively studied in inorganic materials, their potential in organic-based systems remains largely unexplored. Here we demonstrate highly mobile hot carriers in crystalline two-dimensional conjugated coordination polymer Cu3BHT (BHT, benzenehexathiol) films. Leveraging a suite of ultrafast spectroscopic and imaging techniques, we map the microscopic charge transport landscape in Cu3BHT films following non-equilibrium photoexcitation across temporal, spatial and frequency domains, revealing two distinct high-mobility transport regimes. In the non-equilibrium regime, hot carriers achieve an ultrahigh mobility of ~2,000 cm2 V-1 s-1, traversing grain boundaries up to ~300 nm within a picosecond. In the quasi-equilibrium regime, free carriers exhibit Drude-type, band-like transport with a remarkable mobility of ~400 cm2 V-1 s-1 and an intrinsic diffusion length exceeding 1 μm. These findings position two-dimensional conjugated coordination polymers as versatile platforms for advancing organic-based hot carrier applications.

Kg-Scale Synthesis of Ultrathin Single-Crystalline MOF/GO/MOF Sandwich Nanosheets with Elevated Electrochemical Performance

The scalable preparation of 2D ultrathin metal-organic framework (MOF) nanosheets remains a significant challenge due to low stripping efficiency and susceptibility to agglomeration. Herein, a facile strategy is developed for the synthesis of 2D ultrathin single-crystal MOF/graphene oxide (GO)/MOF (MGM) sandwich-like nanosheets based on the Ni/Co-BDC MOF (BDC = 1,4-terephthalic acid), with GO serving as a structure-directing agent. Impressively, 1 kg of MGM nanosheets can be obtained in a single batch with a metal-based yield of 98.73%. Furthermore, the universality of this strategy is implemented by the successful synthesis of three additional 2D ultrathin nanosheets: MGM7-ABDC, MGM7-FBDC, and MGM7-BPDC (metal = Ni, Co; ligands = 2-aminoterephthalic acid (2-ABDC), 2-fluoroterephthalic acid (2-FBDC), and 4,4'- biphenyl dicarboxylic acid (BPDC)). The as-prepared MGM7 nanosheets (Ni: Co ratio = 7:3) exhibit excellent electrochemical performance as the cathode for aqueous basic zinc battery (159.2 mA h g-1 at 1 A g-1), anode for sodium-ion battery (SIB, 593.0 mA h g-1 at 0.2 A g-1), and electrocatalyst for the oxygen evolution reaction (OER, 224 mV overpotential at 10 mA cm-2), significantly outperforming both bulk MOFs and conventional MOF nanosheets. This work enables the scalable synthesis of 2D MOF nanosheets with enhanced properties for multiple applications.

Construction of Heterometallic Coordination Nanosheets Comprising Both Inert and Labile Metal Ions Together via Metalloligand Approach

Construction of coordination nanosheets (CONASHs) containing both inert and labile metal ions together is fundamentally significant but remains synthetically unachievable until now and difficult to realize via conventional synthetic approach of CONASHs due to variable complexation conditions between heterometal ions and organic ligands. Here, we demonstrate a strategy to harness both inert and labile metal ions together into a CONASHs structure by introducing the concept of a metalloligand. Metalloligands comprising inert metal ion (Os2+/Ru2+) and free coordinating sites are designed and synthesized and can be further used as coordinating ligand to bind labile heterometal ion (Fe2+) for building of heterometallic CONASHs (HMCONASHs). Following this, two HMCONASHs containing homoleptic heterometallic complexes are constructed that show broad absorption and electrochemical window with reversible dual redox activity. Further, HMCONASH films exhibit multicolor electrochromism at different voltages, indicating their potential for various applications. This synthetic approach may open a window to create CONASHs with diverse structures and functions that are hard to achieve via a traditional synthetic approach.

A Trimming-π Strategy for Constructing Functional Conductive Metal-Organic Frameworks Using Metalloporphyrazine Units

Developing functional metal-organic frameworks (MOFs) with high electrical conductivity is crucial for their applications as advanced electronic materials. In this work, we for the first time construct a new family of functional and highly conductive MOFs using metalloporphyrazine (MPz) ligands based on a trimming-π concept via cutting the benzene ring from molecular metallopthalocynine (MPc). The deprotonation-after-coordination synthetic method affords crystalline MPz-Cu-NH MOFs with square lattices. Four-point probe conductivity measurements reveal the high room temperature electrical conductivity of MPz-based MOFs ranging from 3.5×10-2 to 1.3×10-1 S cm-1, two orders of magnitude higher than the MPc-based MOF counterparts. Temperature-dependent conductivity measurements and electronic band structure analysis demonstrate ultra-small activation energies with potential metallic conducting behavior for the MPz-Cu-NH MOFs. Encapsulation of the aromatic guest molecules with different electron-donating and -withdrawing features allows the conductivity modulation of the CuPz-Cu-NH in a wide range spanning two orders of magnitude. These conductive MPz-Cu-NH MOFs with built-in MPz functional units exhibit MPz identity-dependent sensing performance, and realize highly sensitive detection of NH3 and NO2 using a low driving voltage of 0.1 V.

2D Rhodium-Isocyanide Frameworks

2D metal-organic frameworks (2D MOFs) are emerging organic van der Waals materials with great potential in various applications owing to their structural diversity, and tunable optoelectronic properties. So far, most reported 2D MOFs rely on metal-heteroatom coordination (e.g., metal-nitrogen, metal-oxygen, and metal-sulfur); synthesis of metal-carbon coordination based 2D MOFs remains a formidable challenge. This study reports the rhodium-carbon (Rh-C) coordination-based 2D MOFs, using isocyanide as the ligand and Rh(I) as metal node. The synthesized MOFs show excellent crystallinity with quasi-square lattice networks. These MOFs show ultra-narrow bandgaps (0.1-0.28 eV) resulting from the interaction between Rh(I) and isocyano groups. Terahertz spectroscopy demonstrates exceptional short-range charge mobilities up to 560 ± 46 cm2 V-1 s-1 in the as-synthesized MOFs. Moreover, these MOFs are used as electrocatalysts for nitrogen reduction reaction and show an excellent NH3 yield rate of 56.0 ± 1.5 µg h-1 mgcat -1 and a record Faradaic efficiency of 87.1 ± 1.8%. In situ experiments reveal dual pathways involving Rh(I) during the catalytic process. This work represents a pioneering step toward 2D MOFs based on metal-carbon coordination and paves the way for novel reticular materials with ultra-high carrier mobility and for versatile optoelectronic devices.

Ligand Regulated the Coordination Environment of Cobalt-Group-MOF for Efficient Electrocatalytic Oxygen Reduction/Evolution Catalysis

In recent years, the TMN4 moieties have demonstrated significant catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in graphene, CxNy, and other carbon-based two-dimensional (2D) support materials. Modifying the coordination number and species of N atoms in the TMN4 moieties has proven to be an effective approach to regulate their catalytic activity. In this research, by incorporating different triphenylene ligands, we have successfully constructed TMA2B2 (TM = Co, Rh, Ir; A/B = N, O, S, Se) moieties with varying coordination environments within 2D metal organic frameworks (MOFs), which are linked by TM and triphenylene. These moieties serve as an effective model to elucidate the structure-property relationship of two-dimensional 2D-MOFs in OER and ORR. Our findings confirm that alterations in the coordination environment can finely tune the d-band electron distribution of the TM within the TMA2B2 unit, particularly activating the dyz and dz2 orbitals of O2, thereby influencing the interactions between TM and key intermediates. We discovered that the regulatory effect of the coordination environment is closely linked to the electronegativity of the coordinating atoms, which led us to establish reliable descriptors such as φ1 and φ2 to elucidate the impact of coordination environments on the performance of OER/ORR. This criterion can be applied to numerous other 2D-MOFs and provides an in-depth understanding of the structure-activity relationship facilitates the development of highly efficient bifunctional electrocatalysts for OER and ORR applications.

Bilayer Metal-Organic Framework Altermagnets with Electrically Tunable Spin-Split Valleys

Bilayer altermagnets featuring layer-mediated spin-valley locking hold significant promise in spintronics and valleytronics. In this study, we perform a comprehensive symmetry analysis of bilayer altermagnets and identify seven spin point group candidates with spin-valley-layer coupling, including 22, 222212, 24̅, 142222, 24̅221m, 1322, and 162222. Focusing on the platform of bilayer metal-organic frameworks, we theoretically design materials with S4 symmetry through chemical modification, achieving spin-splitting in the valence band. Furthermore, the spin valleys from different layers exhibit tunable responses to external static gate electric fields, enabling precise control of spin-splitting. Our findings presented a framework that integrates spin, valley, and layer degrees of freedom in bilayer altermagnets, paving the way for nanoscale spintronics and valleytronics applications.

Tandem Assembly and Etching Chemistry towards Mesoporous Conductive Metal-Organic Frameworks for Sodium Storage Over 50,000 Cycles

Despite two-dimensional (2D) conductive metal-organic frameworks (cMOFs) being attractive due to their intrinsic electrical conductivity and redox activity for energy applications, alleviating the constrained mass transfer within long-range micropore channels remains a significant challenge. Herein, we present a tandem assembly and etching chemistry, to incorporate perpendicularly aligned mesopores into the micropores of cMOFs, via a bi-functional modulator. Synchrotron spectral and morphological analyses demonstrate that the elaborate ammonia modulator first coordinates with Zn2+ forming defects during the initial self-assembly of cMOF oligomers, which then initiates mesoporous cMOFs via in situ etching. In situ spectroscopy and theoretical simulations further reveal that such a unique perpendicular mesoporous structure shorts the micropore channels by two orders of magnitude and relaxes the inherent ion stacking within micropores, leading to five times faster Na+ transport and a remarkable rate capability at 250 C and sodium storage lifespan over 50,000 cycles. Our protocol opens up a new avenue for introducing mesopores into microporous cMOFs for advanced energy applications and beyond.

Two dimensional Conjugated Metal-Organic Frameworks with Multiple Redox-Active Sites towards High-Performance Sodium-Ion Battery

Two dimensional (2D) conjugated metal-organic frameworks (2D c-MOFs) have emerged as promising electroactive materials for energy storage owing to their high conductivity and large charge carrier mobility. However, their broader implementation is hindered by limitations in capacity and cycling stability, primarily due to the restricted density, diversity, and stability of the redox sites. In this study, a new 2D c-MOF (Cu-TTPQ) with multiple redox-active sites that incorporated quinone and pyrazine functionalities as cathode materials for sodium-ion batteries (SIBs) is developed. Notably, 2D layered Cu-TTPQ with a rigid skeleton is directly synthesized from a flexible precursor ligand through in situ cyclodehydrogenation and coordination assembly. Two other contrastive 2D c-MOF analogs (Cu-TBPQ and Cu-DDQP) sharing similar structural motifs with Cu-TTPQ but featuring distinct conductivities and energy band characteristics are prepared for systematic investigation. By contrast, Cu-TTPQ demonstrates a higher reversible capacity of 214.8 mAh g-1 at 0.05 A g-1, along with high cycling stability, showing impressive cyclability with minimal capacity decay even after 1800 cycles at 5.0 A g-1. This work elucidates the rationality of introducing multiple redox-active sites to improve the overall performance of 2D c-MOFs as cathode materials for SIBs.

Evolving Role of Conjugated Polymers in Nanoelectronics and Photonics

Conjugated polymers (CPs) have emerged as an interesting class of materials in modern electronics and photonics, characterized by their unique delocalized π-electron systems that confer high flexibility, tunable electronic properties, and solution processability. These organic polymers present a compelling alternative to traditional inorganic semiconductors, offering the potential for a new generation of optoelectronic devices. This review explores the evolving role of CPs, exploring the molecular design strategies and innovative approaches that enhance their optoelectronic properties. We highlight notable progress toward developing faster, more efficient, and environmentally friendly devices by analyzing recent advancements in CP-based devices, including organic photovoltaics, field-effect transistors, and nonvolatile memories. The integration of CPs in flexible sustainable technologies underscores their potential to revolutionize future electronic and photonic systems. As ongoing research pushes the frontiers of molecular engineering and device architecture, CPs are poised to play an essential role in shaping next-generation technologies that prioritize performance, sustainability, and adaptability.

Homonuclear/Heteronuclear Bimetallic Conjugated Coordination Polymers with Customized Oxygen Evolution Pathway

The reasons for the generally superior performance of synergistic effects in bimetallic catalysts in the oxygen evolution reaction (OER) are not fully understood, largely due to the complexity of catalyst structures and the challenges associated with synthesizing long-range atomic ordering catalysts. In this study, we present a series of two-dimensional (2D) conjugated bimetallic coordination polymers (c-CPs) involving Co or Ni with unambiguous and nearly identical geometry structures for the electrocatalysis of OER, which are highly suitable for discussions on structure-property correlations. The heteronuclear CoNi-PI unexpectedly alters the OER catalytic mechanisms from adsorbate evolution mechanism those observed in homonuclear CoCo-PI and NiNi-PI to the kinetically faster oxide path mechanism, exhibiting high stability and an ultralow overpotential of 282 mV even at 100 mA cm-2 with a Tafel slope of approximately 42 mV dec-1. This study presents an extremely rare crystalline heteronuclear bimetallic catalyst with excellent catalytic properties, promising significant influences in catalyst development research.

The Cu─O─Co Asymmetric Bimetallic Sites Constructed by Ion-Exchange for Efficient Oxygen Evolution Reaction

Recently, constructing oxygen-bridged asymmetric bimetallic sites has proven to be an effective strategy for enhancing electrocatalytic activity. The strong electronic interaction between the metals regulates the d-band center, optimizing the adsorption and desorption of oxygen intermediates and lowering the oxygen evolution reaction (OER) energy barrier. However, examples of constructing such asymmetric sites in π-d conductive metal-organic frameworks (cMOFs) are still scarce. Here, the Co/Cu-DBC (DBC = Dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol) with high crystallinity and asymmetric Cu─O─Co bimetallic sites are prepared using an ion-exchange method. By varying the reaction temperature and time, the metal content can be precisely controlled. The Co/Cu-DBC shows excellent OER activity, with a small overpotential of 251 mV at 10 mA cm-2. Both experimental and density functional theory (DFT) calculations indicate that the construction of asymmetric Cu─O─Co sites leads to strong electronic interactions between Cu and Co through the axial oxygen atom, which regulates the d-band center energy (Ed) level and electronic structure to optimize the adsorption of intermediates and facilitate the formation of *O intermediates on the active Co sites toward fast OER kinetics. This work provides new insights for the synthesis and the design of efficient OER catalysts.

Electronic band structure engineering of π-d conjugated metal-organic framework for sodium organic batteries

Two-dimensional conjugated metal organic frameworks (2D c-MOFs) hold significant promise as electrode materials for alkali metal ion batteries while their electrochemical properties still lack reasonable and effective regulation. Here, two representative 2D c-MOFs (M-HHTQ/M-HHTP, M=Cu or Ni) as positive electrodes are used as models to explore the basic/microscopic principles of their complex storage mechanism in sodium ion batteries (SIBs). It is demonstrated that the energy storage mechanism of 2D c-MOFs is determined by the interaction between coordination covalent bonds and organic linkers. Theoretical calculations and experiment results have jointly demonstrated that the redox potential and theoretical capacity can be regulated based on the valence of M-O bond and the utilization of anions and cations, respectively. As a result, Cu-HHTQ achieves a high discharge voltage at 2.55 V (vs. Na+/Na), a higher stable specific capacity of 208 mAh g-1 at 0.05 A g-1, and long cyclability with the capacity retention rate of 100% at 1 A g-1 after 2000 cycles.

Nanoscale Resist-Free Patterning of Halogenated Zeolitic Imidazolate Frameworks by Extreme UV Lithography

Advancements in patterning techniques for metal-organic frameworks (MOFs) are crucial for their integration into microelectronics. However, achieving precise nanoscale control of MOF structures remains challenging. In this work, a resist-free method for patterning MOFs is demonstrated using extreme ultraviolet (EUV) lithography with a resolution of 40 nm. The role of halogen atoms in the linker and the effect of humidity are analyzed through in situ and near-ambient pressure synchrotron X-ray photoelectron spectroscopy. In addition to facilitating the integration of MOFs, the results offer valuable insights for developing the highly sought-after positive-tone EUV photoresists.

Two-dimensional conjugated metal-organic frameworks for electrochemical energy conversion and storage

Effective electrocatalysts and electrodes are the core components of energy conversion and storage systems for sustainable carbon and nitrogen cycles to achieve a carbon-neutral economy. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as multifunctional materials for electrochemical applications benefiting from their similarity to graphene with remarkable conductivity, abundant active sites, devisable components, and well-defined crystalline structures. In this review, the structural design strategies to establish active components with a maximum degree through redox-active ligand assembly in 2D c-MOFs are briefly summarized. Next, recent representative examples of 2D c-MOFs applied in electrocatalysis (hydrogen/oxygen evolution and oxygen/carbon dioxide/nitrogen reduction) and energy storage systems (supercapacitors and batteries) are introduced. The synergistic effect of multiple components in 2D c-MOFs is particularly emphasized for enhanced performance in electrochemical energy conversion and storage systems. Finally, an outlook and challenges are proposed for realizing more active components, elucidating the reaction mechanism involving the derived structures, and achieving low-cost economy in practical applications.

Synthesizing Conductive Metal-Organic Framework Nanosheets for High-Performing Chemiresistive Sensors

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are emerging as unique electrode materials with great potential for electronic applications. However, traditional devices based on c-MOFs often utilize them directly in the powder or nanoparticle form, leading to weak adhesion to the device substrate and resulting in low stability and high noise levels in the final device. In this study, we present a novel approach utilizing thin c-MOFs synthesized via a general MOF nanosheet sacrifice approach, enhancing their aspect ratio and flexibility for high-performance electronic applications. The resultant benzene-based Cu-BHT nanosheets feature a thin thickness (around 5 nm) and a high aspect ratio (>100), affording Cu-BHT exceptional flexibility with a 10-fold decrease in Young's modulus (0.98 GPa) and hardness (0.09 GPa) compared to bulk Cu-BHT nanoparticles (10.79 and 0.75 GPa, respectively). This heightened flexibility enables the Cu-BHT nanosheets to conform to the channels of the electrodes, ensuring robust adhesion to the electrode substrate and improving device stability. As a proof-of-concept, the chemiresistive nanosensor based on Cu-BHT nanosheets demonstrates an 8.0-fold decrease in the coefficient of variation of the response intensity and a 47.1-fold increase in the signal-to-noise ratio compared to sensors based on bulk Cu-BHT nanoparticles. Combined with the machine learning algorithms, the Cu-BHT nanosensor demonstrates outstanding performance in identifying and discriminating multiple volatile organic compounds at room temperature with an average accuracy of 97.9%, surpassing the thus-far-reported chemiresistive sensors.

Dual-MOF-Layered Films via Solution Shearing Approach: A Versatile Platform for Tunable Chemiresistive Sensors

Metal-organic frameworks (MOFs) are ideal for gas sensing due to their high porosity and chemical diversity. However, their low electrical conductivity has traditionally limited their application in chemiresistive-type sensors. The recent development of electrically conductive MOFs (cMOFs) has addressed this limitation. However, directly designing cMOFs with specific sensing properties remains challenging due to the limited understanding of their structure-property relationships. At this stage, the synergistic integration of cMOFs with conventional insulating MOFs has emerged as a viable solution, enabling diverse gas interactions and the rational design of sensing properties. Despite this potential, exploration of the diverse roles of MOFs in such composites remains underutilized. Herein, we develop a series of MOF-on-cMOF sensors and demonstrate their tunable sensing properties. A two-step solution-shearing-based film fabrication method enables facile integration of cMOFs with a wide range of conventional MOFs in layered structures. On cMOF thin film as a primary sensing layer, secondary MOF layers with different pore structures and adsorption properties were strategically selected and deposited. These layered film sensors exhibited tunable sensing properties, including enhanced sensitivity, selectivity, response speed, and recovery for analytes such as NH3, H2S, and NO2. These improvements cannot be achieved solely through the conventional role of MOFs as sieving layers. Furthermore, computational analyses elucidated the structure-property relationships underlying these improvements, offering key insights into the rational design of MOF-based gas sensors.

Selective On-Surface Metalation and Uncommon Reordering of Self-Assembled Macrocyclic Biquinazoline Ligands on Ag(111)

The macrocyclic biquinazoline ligand, H-Mabiq, presents a central and a peripheral site for the coordination of metal atoms, making the adsorption on solid surfaces promising for the creation of self-assembled bimetallic two-dimensional platforms. Here, we apply an on-surface metalation strategy under ultra-high vacuum conditions to guide the synthesis of metalated species and study sequential metalation patterns. We find that cobalt (as well as iron) metalation on the Ag(111) surface preferentially occurs at the macrocyclic centre without further metal coordination to the peripheral site. Nevertheless, starting from a densely packed, self-assembled H-Mabiq monolayer, the modification of the central cavity by Co is accompanied by an unusual, metalation-induced phase transformation, which gives evidence of modified lateral / interfacial interactions. The selective metalation of one molecular site opens up an on-surface route to create bimetallic networks incorporating select metal ions at different locations.

Conductive Metal-Organic Frameworks and Their Electrocatalysis Applications

Recently, electrically conductive metal-organic frameworks (EC-MOFs) have emerged as a wealthy library of porous frameworks with unique properties, allowing their use in diverse applications of energy conversion, including electrocatalysis. In this review, the electron conduction mechanisms in EC-MOFs are examined, while their electrical conductivities are considered. There have been various strategies to enhance the conductivities of MOFs including ligand modification, the incorporation of conducting materials, and the construction of multidimensional architectures. With sufficient conductivities being established for EC-MOFs, there have been extensive pursuits in their electrocatalysis applications, such as in the hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, N2 reduction reaction, and CO2 reduction reaction. In addition, computational modeling of EC-MOFs also exerts an important impact on revealing the synthesis-structure-performance relationships. Finally, the prospects and current challenges are discussed to provide guidelines for designing promising framework materials.

Rational Construction of Layered Two-Dimensional Conjugated Metal-Organic Frameworks with Room-Temperature Quantum Coherence

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as an intriguing class of quantum materials due to their high crystallinity, persistent spin centers, and tunable structures and topologies. However, it remains unclear how to achieve long spin relaxation time at room temperature in 2D c-MOFs via a bottom-up design strategy. Herein, we design a hexahydroxytrithiatruxene ligand (HHTH) to minimize the influence of nuclear spin on electron spin relaxation while weakening d-π conjugation to construct a "spin docking" for preserving spin centers, which enables the resulting 2D c-MOFs, Ni3HHTH2, to exhibit quantum coherence and Rabi oscillations at room temperature. Spin dynamics studies not only reveal an unusual temperature-dependent Rabi frequency in Ni3HHTH2 but also indicate that the coordination mode determines the spin-lattice relaxation behavior via spin-phonon coupling. These investigations provide a general guideline for the development of high-performance quantum qubits based on 2D spin arrays.

2D Conjugated Metal-Organic Framework-Based Composite Membranes for Nanofluidic Ionic Photoelectric Conversion

Nanofluidic photoelectric conversion system based on photo-excitable 2D materials can directly transduce light stimuli into an ion-transport-mediated electric signal, showing potential for mimicking the retina's function with a more favorable human-robot interactions. However, the current membranes suffer from low generation efficiency of charge carriers due to the mixed microstructure and limited charge transport ability caused by the large interlayer spacing and monotonous pathway. Here, a fully conjugated 2D hexaimino-substituted triphenylene-based metal-organic framework (2D-HATP-cMOF) based composite membrane with high conductivity for photoelectric conversion is presented. The extended π-d conjugation within the ab plane and the favorable transport pathway through π-π stacking of the c-MOF maximize the generation and transfer of charge carrier and greatly accelerate the ion transport. As a result, the 2D-HATP-cMOF-based composite membrane possesses ultrafast photoelectric response, superior to other reported 2D systems like graphene oxide (GO), transition metal carbides, carbonitrides and nitrides (MXene), and MoS2, which require at least 10 s. A successful ion pump phenomenon, that is active transport from low concentration to high concentration as an important way of information transmission in organisms, is realized based on the efficient photoelectric conversion capability. This work demonstrates the great promise of 2D c-MOF in ionic photoelectric conversion.

Metal-organic framework-based smart stimuli-responsive drug delivery systems for cancer therapy: advances, challenges, and future perspectives

Cancer treatment is currently one of the most critical healthcare issues globally. A well-designed drug delivery system can precisely target tumor tissues, improve efficacy, and reduce damage to normal tissues. Stimuli-responsive drug delivery systems (SRDDSs) have shown promising application prospects. Intelligent nano drug delivery systems responsive to endogenous stimuli such as weak acidity, complex redox characteristics, hypoxia, active energy metabolism, as well as exogenous stimuli like high temperature, light, pressure, and magnetic fields are increasingly being applied in chemotherapy, radiotherapy, photothermal therapy, photodynamic therapy, and various other anticancer approaches. Metal-organic frameworks (MOFs) have become promising candidate materials for constructing SRDDSs due to their large surface area, tunable porosity and structure, ease of synthesis and modification, and good biocompatibility. This paper reviews the application of MOF-based SRDDSs in various modes of cancer therapy. It summarizes the key aspects, including the classification, synthesis, modifications, drug loading modes, stimuli-responsive mechanisms, and their roles in different cancer treatment modalities. Furthermore, we address the current challenges and summarize the potential applications of artificial intelligence in MOF synthesis. Finally, we propose strategies to enhance the efficacy and safety of MOF-based SRDDSs, ultimately aiming at facilitating their clinical translation.

Tuning the Structure-Property Relationships of Metallophthalocyanine-Based Two-Dimensional Conductive Metal-Organic Frameworks with Different Metal Linkages

Metallophthalocyanine (MPc)-linked conductive two-dimensional (2D) metal-organic frameworks (MOFs) hold tremendous promise as modular 2D materials in sensing, catalysis, and energy-related applications due to their combinatory bimetallic system from the MPc core and bridging metal nodes, endowing them with high electrical conductivity and multifunctionality. Despite significant advances, there is a gap in fundamental understanding regarding the periodic effects of metal nodes on the structural properties of MPc-linked 2D MOFs. Herein, we report a series of highly crystalline MOFs wherein copper phthalocyanine (CuPc) is linked with Ni, Cu, and Zn nodes (CuPc-O-M, M: Ni, Cu, Zn). The prepared CuPc-O-M MOFs exhibit p-type semiconducting properties with an exceptionally high range of electrical conductivity. Notably, the differences in the 3d orbital configurations of the Ni, Cu, and Zn nodes in CuPc-O-M MOFs lead to perturbations of the interlayer stacking patterns of the 2D framework materials, which ultimately affect material properties, such as semiconducting band gaps and charge transport within the framework. The Cu2+ (3d9) metal node within the eclipsed interlayer stacking of CuPc-O-Cu MOF demonstrates excellent charge transport, which results in the smallest band gap of 1.14 eV and the highest electrical conductivity of 9.3 S m-1, while the Zn2+ (3d10) metal node within CuPc-O-Zn results in a slightly inclined interlayer stacking, leading to the largest band gap of 1.27 eV and the lowest electrical conductivity of 2.9 S m-1. These findings form an important foundation in the strategic molecular design of this class of materials for multifaceted functionality that builds upon the electronic properties of these materials.

Mechanistic Insights into Solvent-Mediated Halide-Specific Irreversible Transformation of Cu-MOF with Iodide Detection Capability

The fascinating feature of metal-organic frameworks is that they can respond to external stimuli, unlike other inorganic materials. This feature corresponds to the framework's flexibility, which originates with the long-range crystalline order of the framework accompanied by cooperative structural transformability. We have synthesized a novel metal-organic framework comprised of Cu(I) nodes with pyrazine linkers and benzene-1,3,5-tricarboxylate acting as template anions, named CUCAM-1 [Cu(Py)2(BTC)]n. In the presence of polar solvent systems, CUCAM-1 undergoes an irreversible structural transformation to yield a mixed phase that consists of HKUST-1 [Cu3(BTC)2(H2O)3]n and another CUCAM-2 [Cu(Py)(BTC)]n MOFs, whose novel structure is successfully revealed by continuous rotation electron diffraction from the mixture. In this structural transformation, a new ligand exchange occurs where template anions become ligands, confirmed by single crystal X-ray analysis. Further, structural transformation and the mechanism are explained by ab initio molecular dynamics (AIMD) simulations. Interestingly, different halides (F-, Cl-, and Br-) can be accompanied to affect/control the composition of the second phase by favoring the formation of the HKUST-1 phase over CUCAM-2, which was evident by the powder X-ray diffraction studies. Furthermore, the structural transformation induced by I- resulted in a colorimetric response due to the formation of a new MOF CUCAM-3, paving the way for use as an iodide detector.

Coexistence of Redox-Active Metal and Ligand Sites in Copper-Based Two-Dimensional Conjugated Metal-Organic Frameworks as Active Materials for Battery-Supercapacitor Hybrid Systems

Two-dimensional (2D) conjugated metal-organic frameworks (c-MOFs) are promising materials for supercapacitor (SC) electrodes due to their high electrochemically accessible surface area coupled with superior electrical conductivity compared to traditional MOFs. In this work, porous and non-porous HHB-Cu (HHB=hexahydroxybenzene), derived through surfactant-assisted synthesis are studied as representative 2D c-MOF models with different characteristics, showing diverse reversible redox reactions with Na+ and Li+ in aqueous (10 M NaNO3) and organic (1.0 M LiPF6 in ethylene carbonate and dimethyl carbonate) electrolytes, respectively. These redox activities were here deployed to design negative electrodes for hybrid SCs (HSCs), combining the battery-like property of HHB-Cu at the negative electrode and the high capacitance and robust cyclic stability of activated carbon (AC) at the positive electrodes. In the organic electrolyte, porous HHB-Cu-based HSC achieves a maximum cell specific capacity (Cs) of 22.1 mAh g-1 at 0.1 A g-1, specific energy (Es) of 15.55 Wh kg-1 at specific power (Ps) of 70.49 W kg-1, and 77 % cyclic stability after 3000 gravimetric charge-discharge (GCD) cycles at 1 A g-1 (specific metrics calculated on the mass of both electrode materials). In the aqueous electrolyte, porous HHB-Cu-based HSC displays a Cs of 13.9 mAh g-1 at 0.1 A g-1, Es of 6.13 Wh kg-1 at 44.05 W kg-1, and 72.3 % Cs retention after 3000 GCD cycles. The non-porous sample, interesting for its superior electrical conductivity despite its limited surface area compared to its porous counterpart, shows lower Es performance but better rate capability compared to the porous one. This study indicates the potential of assembling a battery-SC hybrid system by rationally exploiting the battery-like behavior of 2D c-MOFs and the electrochemical double-layer capacitance of AC.

From 0D to 2D: microwave-assisted synthesis of electrically conductive metal-organic frameworks with controlled morphologies

Morphology control of electrically conductive metal-organic frameworks (EC-MOFs) can be a powerful means to tune their surface area and carrier transport pathways, particularly beneficial for energy conversion and storage. However, controlling EC-MOFs' morphology is underexplored due to the uncontrollable crystal nucleation and rapid growth kinetics. This work introduces a microwave-assisted strategy to readily synthesize Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with controlled morphologies. We controlled solvent compositions to facilitate particles' directional growth to 1D and 2D crystals. Meanwhile, we found that ultrasonication can manipulate crystal seeding, yielding 0D spherical Cu-HHTP crystals. Electronic conductivity measurements suggest that the isotropic nature of the 0D crystals allows a conductivity of 7.34 × 10-1 S cm-1, much higher than 1D and 2D counterparts. Additionally, the controlled 0D morphology enhanced the material's capacitance and effective surface area and significantly improved its photocurrent response. These findings underscore the pivotal impact of controlled morphology in optimizing EC-MOFs' physicochemical properties.

A 3D four-fold interpenetrated conductive metal-organic framework for fast and robust sodium-ion storage

Two-dimensional conductive metal-organic frameworks (2D c-MOFs) with high electrical conductivity and tunable structures hold significant promise for applications in metal-ion batteries. However, the construction of 3D interpenetrated c-MOFs for applications in metal-ion batteries is rarely reported. Herein, a 3D four-fold interpenetrated c-MOF (Cu-DBC) constructed by conjugated and contorted dibenzo[g,p]chrysene-2,3,6,7,10,11,14,15-octaol (DBC) ligands is explored as an advanced cathode material for sodium-ion batteries (SIBs) for the first time. Notably, the expanded conjugated and four-fold interpenetrating structure endows Cu-DBC with transmission channels for electrons and sufficient spacing for sodium ion diffusion. As expected, the Cu-DBC cathode showcases higher specific capacity (120.6 mA h g-1, 0.05 A g-1) and robust cycling stability (18.1% capacity fade after 4000 cycles, 2 A g-1). Impressively, the Cu-DBC cathode also exhibits good electrochemical properties at extreme temperatures (-20 °C and 50 °C). A series of in/ex situ characterizations and systematic theoretical calculations further reveal the sodium-ion storage mechanism of Cu-DBC, highlighting a three-electron redox process on the redox-active [CuO4] units. This work provides valuable insights for exploring and enriching the applications of 3D interpenetrated c-MOFs in metal-ion batteries.

Two-Dimensional Conjugated Metal-Organic Frameworks for Photochemical Transformations

Photochemical transformation represents an attractive pathway for the conversion of earth-abundant resources, such as H2O, CO2, O2, and N2, into valuable chemicals by utilizing sunlight as an energy source. Recently, two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as the focal points in the field of photo-to-chemical conversion due to their advantages in light harvesting, electrical conductivity, mass transport, tunable electronic and porous structures, as well as abundant active sites. In this review, we highlight various physical and chemical features of 2D c-MOFs that can contribute to enhanced photo-induced exciton generation, charge transport, proton migration and redox catalysis. Then, the existing strategies to integrate suitable light absorbers and/or co-catalysts onto 2D c-MOFs for photochemical transformations (with a particular focus on H2 evolution, CO2 reduction and O2 reduction) have been discussed. Finally, the challenges and opportunities of using 2D c-MOFs in other photochemical applications (e.g., N2 fixation, organic synthesis, and environmental remediation) are assessed.

Metal-Phthalocyanine-Based Two-Dimensional Conjugated Metal-Organic Frameworks for Electrochemical Glycerol Oxidation Reaction

Electrochemical glycerol oxidation reaction (GOR) is a promising candidate to couple with cathodic reaction, like hydrogen evolution reaction, to produce high-value product with less energy consumption. Two dimensional conjugated metal-organic frameworks (2D c-MOFs), comprising square-planar metal-coordination motifs (e.g., MO4, M(NH)4, MS4), are notable for their programable active sites, intrinsic charge transport, and excellent stability, making them promising catalyst candidates for GOR. In this study, we introduce a novel class of 2D c-MOFs electrocatalysts, M2[NiPcS8] (M=Co/Ni/Cu), which are synthesized via coordination of octathiolphthalocyaninato nickel (NiPc(SH)8) with various metal centers. Due to a fast kinetic and high activity of CoS4 sites for GOR, the electrocatalytic tests demonstrate that Co2[NiPcS8] supported on carbon paper displays a low GOR potential of 1.35 V vs. RHE at 10 mA cm-2, significantly reducing the overall water-electrolysis-voltage reduction by 0.27 V from oxygen evolution reaction to GOR, thereby outperforming Ni2[NiPcS8] and Cu2[NiPcS8]. Additionally, we have determined that the GOR activity of CoX4 linkage sites varies with different heteroatoms, following an experimentally and theoretically confirmed activity order of CoS4>CoO4>Co(NH)4. The GOR performance of Co2[NiPcS8] not only demonstrate superior performance among non-noble metal complex, but also provides critical insights on designing high-performance MOF electrocatalysts upon optimizing the electronic environment of active sites.

Mechanistic Insight into the Formation and Deposition of Conductive, Layered Metal-Organic Framework Nanocrystals

This paper describes the use of the layered conductive metal-organic framework (MOF) (nickel)3-(hexahydroxytriphenylene)2 [Ni3(HHTP)2] as a model system for understanding the process of self-assembly within this class of materials. We confirm and quantify experimentally the role of the oxidant in the synthetic process. Monitoring the deposition of Ni3(HHTP)2 with in situ infrared spectroscopy revealed that MOF formation is characterized by an initial induction period, followed by linear growth with respect to time. The presence and identity of oxidizing agents is critical for the coordination-driven self-assembly of these materials and impacts both the length of the induction period and the observed rate of MOF growth. A large excess of hydrogen peroxide results in a 2× increase in the observed deposition rate (9.6 ± 6.8 × 10-4 vs 5.0 ± 2.8 × 10-4 min-1) over standard reaction conditions, but leads to the formation of large, irregularly shaped particles. Slower deposition rates in the presence of oxygen favor the formation of uniformly sized nanorods (98 ± 38 × 25 ± 6 nm). These quantitative insights into the mechanism of HHTP-based MOF formation provide valuable information about the fundamental aspects of coordination and polymerization that are critical for nanoscale crystal engineering of structure-property relationships in this class of materials.

Two-Dimensional Organic-Inorganic van der Waals Hybrids

Two-dimensional organic-inorganic (2DOI) van der Waals hybrids (vdWhs) have emerged as a groundbreaking subclass of layer-stacked (opto-)electronic materials. The development of 2DOI-vdWhs via systematically integrating inorganic 2D layers with organic 2D crystals at the molecular/atomic scale extends the capabilities of traditional 2D inorganic vdWhs, thanks to their high synthetic flexibility and structural tunability. Constructing an organic-inorganic hybrid interface with atomic precision will unlock new opportunities for generating unique interfacial (opto-)electronic transport properties by combining the strengths of organic and inorganic layers, thus allowing us to satisfy the growing demand for multifunctional applications. Here, this review provides a comprehensive overview of the latest advancements in the chemical synthesis, structural characterization, and numerous applications of 2DOI-vdWhs. Firstly, we introduce the chemistry and the physical properties of the recently rising organic 2D crystals (O2DCs), which feature crystalline 2D nanostructures comprising carbon-rich repeated units linked by covalent/noncovalent bonds and exhibit strong in-plane extended π-conjugation and weak interlayer vdWs interaction. Simultaneously, representative inorganic 2D crystals (I2DCs) are briefly summarized. After that, the synthetic strategies will be systematically summarized, including synthesizing single-component O2DCs with dimensional control and their vdWhs with I2DCs. With these synthetic approaches, the control in the dimension, the stacking modes, and the composition of the 2DOI-vdWhs will be highlighted. Subsequently, a special focus will be given on the discussion of the optical and electronic properties of the single-component 2D materials and their vdWhs, which will be closely relevant to their structures, so that we can establish a general structure-property relationship of 2DOI-vdWhs. In addition to these physical properties, the (opto-)electronic devices such as transistors, photodetectors, sensors, spintronics, and neuromorphic devices as well as energy devices will be discussed. Finally, we provide an outlook to discuss the key challenges for the 2DOI-vdWhs and their future development. This review aims to provide a foundational understanding and inspire further innovation in the development of next-generation 2DOI-vdWhs with transformative technological potential.

Ligand-Insertion Strategy for Constructing 2D Conjugated Metal-Organic Framework with Large Pore Size for Electrochemical Analytics

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have shown great promise in various electrochemical applications due to their intrinsic electrical conductivity. A large pore aperture is a favorable feature of this type of material because it facilitates the mass transport of chemical species and electrolytes. In this work, we propose a ligand insertion strategy in which a linear ligand is inserted into the linkage between multitopic ligands, extending the metal ion into a linear unit of -M-ligand-M-, for the construction of 2D c-MOFs with large pore apertures, utilizing only small ligands. As a proof-of-concept trial of this strategy, a 2D c-MOF with mesopores of 3.2 nm was synthesized using commercially available ligands hexahydrotriphenylene and 2,5-dihydroxybenzoquinone. The facilitation of the diffusion of redox species by the large pore size of this MOF was demonstrated through a series of probes. With this feature, it showed superior performance in the electrochemical analysis of a variety of biological species.

Modification of metals and ligands in two-dimensional conjugated metal-organic frameworks for CO2 electroreduction: A combined density functional theory and machine learning study

Electrochemical carbon dioxide reduction reaction (CO2RR) is a promising technology to establish an artificial carbon cycle. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) with high electrical conductivity have great potential as catalysts. Herein, we designed a range of 2D c-MOFs with different transition metal atoms and organic ligands, TMNxO4-x-HDQ (TM = Cr∼Cu, Mo, Ru∼Ag, W∼Au; x  = 0, 2, 4; HDQ = hexadipyrazinoquinoxaline), and systematically studied their catalytic performance using density functional theory (DFT). Calculation results indicated that all of TMNxO4-x-HDQ structures possess good thermodynamic and electrochemical stability. Notably, among the examined 37 MOFs, 6 catalysts outperformed the Cu(211) surface in terms of catalytic activity and product selectivity. Specifically, NiN4-HDQ emerged as an exceptional electrocatalyst for CO production in CO2RR, yielding a remarkable low limiting potential (UL) of -0.04 V. CuN4-HDQ, NiN2O2-HDQ, and PtN2O2-HDQ also exhibited high activity for HCOOH production, with UL values of -0.27, -0.29, and -0.27 V, respectively, while MnN4-HDQ, and NiO4-HDQ mainly produced CH4 with UL values of -0.58 and -0.24 V, respectively. Furthermore, these 6 catalysts efficiently suppressed the competitive hydrogen evolution reaction. Machine learning (ML) analysis revealed that the key intrinsic factors influencing CO2RR performance of these 2D c-MOFs include electron affinity (EA), electronegativity (χ), the first ionization energy (Ie), p-band center of the coordinated N/O atom (εp), the radius of metal atom (r), and d-band center (εd). Our findings may provide valuable insights for the exploration of highly active and selective CO2RR electrocatalysts.

Two-Periodic MoS2-Type Metal-Organic Frameworks with Intrinsic Intralayer Porosity for High-Capacity Water Sorption

2D metal-organic frameworks (2D-MOFs) are an important class of functional porous materials. However, the low porosity and surface area of 2D-MOFs have greatly limited their functionalities and applications. Herein, the rational synthesis of a class of mos-MOFs with molybdenum disulfide (mos) net based on the assembly of trinuclear metal clusters and 3-connected tripodal organic ligands is reported. The non-crystallographic (3,6)-connected mos net, different from the 3-connected hcb net of graphene, offers abundant intralayer voids courtesy of the split of one node into two. Indeed, mos-MOFs exhibit high apparent Brunauer-Emmett-Teller surface areas, significantly superior to those of other 2D-MOF analogs. Markedly, hydrolytically stable Cr-mos-MOF-1 displays an impressive water vapor uptake of 0.75 g g-1 at 298 K and P/P0 = 0.9, among the highest in 2D-MOFs. The combined water adsorption and X-ray diffraction study reveal the water adsorption mechanisms, suggesting the importance of intralayer porosities of mos-MOFs for high-performance water capture. This study paves the way for a reliable approach to synthesizing 2D-MOFs with high porosity and surface areas for diverse applications.

Precision-Engineered Construction of Proton-Conducting Metal-Organic Frameworks

Proton-conducting materials have attracted considerable interest because of their extensive application in energy storage and conversion devices. Among them, metal-organic frameworks (MOFs) present tremendous development potential and possibilities for constructing novel advanced proton conductors due to their special advantages in crystallinity, designability, and porosity. In particular, several special design strategies for the structure of MOFs have opened new doors for the advancement of MOF proton conductors, such as charged network construction, ligand functionalization, metal-center manipulation, defective engineering, guest molecule incorporation, and pore-space manipulation. With the implementation of these strategies, proton-conducting MOFs have developed significantly and profoundly within the last decade. Therefore, in this review, we critically discuss and analyze the fundamental principles, design strategies, and implementation methods targeted at improving the proton conductivity of MOFs through representative examples. Besides, the structural features, the proton conduction mechanism and the behavior of MOFs are discussed thoroughly and meticulously. Future endeavors are also proposed to address the challenges of proton-conducting MOFs in practical research. We sincerely expect that this review will bring guidance and inspiration for the design of proton-conducting MOFs and further motivate the research enthusiasm for novel proton-conducting materials.

Solution-Processable MOF-on-MOF System Constructed via Template-Assisted Growth for Ultratrace H2S Detection

Conductive metal-organic frameworks (c-MOFs) hold promise for highly sensitive sensing systems due to their conductivity and porosity. However, the fabrication of c-MOF thin films with controllable morphology, thickness, and preferential orientation remains a formidable yet ubiquitous challenge. Herein, we propose an innovative template-assisted strategy for constructing MOF-on-MOF (Ni3(HITP)2/NUS-8 (HITP: 2,3,6,7,10,11-hexamino-tri (p-phenylene))) systems with good electrical conductivity, porosity, and solution processability. Leveraging the 2D nature and solution processability of NUS-8, we achieve the controllable self-assembly of Ni3(HITP)2 on NUS-8 nanosheets, producing solution-processable Ni3(HITP)2/NUS-8 nanosheets with a film conductivity of 1.55×10-3 S ⋅ cm-1 at room temperature. Notably, the excellent solution processability facilitates the fabrication of large-area thin films and printing of intricate patterns with good uniformity, and the Ni3(HITP)2/NUS-8-based system can monitor finger bending. Gas sensors based on Ni3(HITP)2/NUS-8 exhibit high sensitivity (LOD~6 ppb) and selectivity towards ultratrace H2S at room temperature, attributed to the coupling between Ni3(HITP)2 and NUS-8 and the redox reaction with H2S. This approach not only unlocks the potential of stacking different MOF layers in a sequence to generate functionalities that cannot be achieved by a single MOF, but also provides novel avenues for the scalable integration of MOFs in miniaturized devices with salient sensing performance.

A highly conducting tetrathiafulvalene-tetracarboxylate based dysprosium(iii) 2D metal-organic framework with single molecule magnet behaviour

The synthesis and whole characterization by a multitechnique approach of an unprecedented dysprosium(iii) 2D metal organic framework (MOF), involving the redox-active tetrathiafulvalene (TTF)-based linker TTF-tetracarboxylate (TTF-TC), are herein reported. The single-crystal X-ray structure, formulated as [Dy6(TTF-TC)5(H2O)22]·21H2O (1), reveals a complex 2D topology, with hexanuclear Dy6 clusters as secondary building units (SBUs) interconnected by five linkers, stacked almost parallel in each layer and eclipsed along the [111] direction, leading to the formation of 1D channels filled by water molecules. The mixed valence of the TTF units is confirmed by both bond distance analysis, Raman microscopy and diffuse reflectance spectroscopy, and further supported by band structure calculations, which also predict activated conductivity for this material. Thanks to efficient TTF stacking and partial oxidation, 1 shows semiconducting behavior, with, however, a record conductivity value of 1 mS cm-1 at room temperature, when compared to the previously reported TTF-based MOFs. Furthermore, temperature and magnetic field dependent ac (alternative current) magnetic susceptibility measurements demonstrate field induced slow relaxation of magnetization, accounting for two independent relaxation processes, with an energy barrier (U eff/K) of around 12 K, typical for dysprosium carboxylate complexes. The herein reported 2D Dy-MOF provides a valuable master plan for coexistence of conducting π-TTF stacks and highly anisotropic DyIII SMM properties.

Construction of 2D zinc(II) MOFs with tricarboxylate and N-donor mixed ligands for multiresponsive luminescence sensors and CO2 adsorption

The solvothermal reactions of ZnCl2·6H2O, benzene-1,3,5-tribenzoic acid (H3btb), and N-heterocyclic ancillary imidazole (Im) or aminopyrimidine (a mp) ligands led to the creation of two-dimensional (2D) zinc(II) based metal-organic frameworks (MOFs), (Me2NH2)2[Zn2(btb)2(Im)2]·2DMF·3MeOH (1) and (Me2NH2)2[Zn2(btb)2(amp)]·H2O·2DMF·MeOH (2). The btb3- ligands in 1 and 2 form an anionic 2D layered structure with a (63) honeycomb (hcb) topology by linking to Zn(II) centres through their carboxylate groups. The incorporation of N-heterocyclic auxiliary ligands Im and amp into the hcb nets resulted in the formation of a 2D hydrogen-bonded and covalently pillared bilayer structure featuring two-fold interpenetrating networks. Each of these networks consists of small channels that are occupied by Me2NH2 cations and solvent molecules. Both 1 and 2 emit blue luminescence emissions in the solid state at room temperature and exhibit a great selectivity and sensitivity for the detection of acetone and multiple heavy metal ions including Hg2+, Cu2+, Fe2+, Pb2+, Cr3+, and Fe3+ ions. At 1 bar, activated 1 and 2 demonstrate moderate capacities for adsorbing CO2 at room temperature, with a preference for CO2 over N2. Notably, at higher pressures (up to 20 bar), their activated samples 1 and 2 show a temperature-dependent enhancement of CO2 uptake while retaining good stability.

Solid-State Electrochemical Carbon Dioxide Capture by Conductive Metal-Organic Framework Incorporating Nickel Bis(diimine) Units

This paper presents the first implementation of electrically conductive metal-organic framework (MOF) Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) integrated with nickel bis(diimine) (Ni-BDI) units for efficient solid-state electrochemical carbon dioxide (CO2) capture. The electrochemical cell assembled using Ni3(HITP)2 as working electrodes can reversibly capture and release CO2 through potential control. A high-capacity utilization of 96% and a Faraday efficiency of 98% have been achieved. The material also exhibits excellent electrochemical stability with its capacity maintained during 50 capture-release cycles and resistance to general interferences, including O2, H2O, NO2, and SO2. Capacity utilization of up to 35% is obtained at CO2 concentrations as low as 1%. The capture of CO2 at concentrations ranging from 1% to 100% requires exceptionally low energy consumption of only 30.5-72.4 kJ mol-1. Studies combining spectroscopic experiments and computational approaches reveal that the CO2 capture and release mechanism involves reversible carbamate formation on the N atom of the Ni-BDI unit in the MOF upon its one-electron redox reaction.

Topological Band Engineering of One-Dimensional π-d Conjugated Metal-Organic Frameworks

One-dimensional (1D) π-d conjugated metal-organic frameworks (c-MOFs) have garnered widespread research interest in chemical energy storage and conversion. In this work, we introduce a universal principle to engineer the topological bands of 1D c-MOFs. Connected by d orbitals of transition metals, two equivalent hidden molecular π orbitals in 1D c-MOFs can generate a staggered hopping within and between the organic ligands, forming Su-Schrieffer-Heeger-shaped 1D topological bands. Guided by this discovery, we investigate the electronic structures of the typical 1D c-MOF assembled from Ni atoms and 2HQDI (QDI = 2,5-diamino-1,4-benzoquinonediimine) precursors (NiQDI) by first-principles calculations, revealing 1D topological bands around the Fermi level. Due to local bonding variations at the QDI terminations, these two hidden molecular π orbitals become atomically bonded but electronically separated at the edge QDI, creating spatially localized in-gap topological edge states at the end of the NiQDI chain. This definitive signature for 1D topological bands is identified through differential conductance spectra in scanning tunneling microscopy measurements. Our results provide conclusive experimental evidence for topological bands in 1D c-MOFs, paving the way for exploring the topological physics in organic materials through frontier molecular orbitals.

Electrodeposition of Ni/Cu Bimetallic Conductive Metal-Organic Frameworks Electrocatalysts with Boosted Oxygen Reduction Activity for Zinc-Air Batteries

Zinc-air batteries employing non-Pt cathodes hold significant promise for advancing cathodic oxygen reduction reaction (ORR). However, poor intrinsic electrical conductivity and aggregation tendency hinder the application of metal-organic frameworks (MOFs) as active ORR cathodes. Conductive MOFs possess various atomically dispersed metal centers and well-aligned inherent topologies, eliminating the additional carbonization processes for achieving high conductivity. Here, a novel room-temperature electrochemical cathodic electrodeposition method is introduced for fabricating uniform and continuous layered 2D bimetallic conductive MOF films cathodes without polymeric binders, employing the organic ligand 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and varying the Ni/Cu ratio. The influence of metal centers on modulating the ORR performance is investigated by density functional theory (DFT), demonstrating the performance of bimetallic conductive MOFs can be effectively tuned by the unpaired 3d electrons and the Jahn-Teller effect in the doped Cu. The resulting bimetallic Ni2.1Cu0.9(HITP)2 exhibits superior ORR performance, boasting a high onset potential of 0.93 V. Moreover, the assembled aqueous zinc-air battery demonstrates high specific capacity of 706.2 mA h g-1, and exceptional long-term charge/discharge stability exceeding 1250 cycles.

Synthesis and structure of a non-van-der-Waals two-dimensional coordination polymer with superconductivity

Two-dimensional conjugated coordination polymers exhibit remarkable charge transport properties, with copper-based benzenehexathiol (Cu-BHT) being a rare superconductor. However, the atomic structure of Cu-BHT has remained unresolved, hindering a deeper understanding of the superconductivity in such materials. Here, we show the synthesis of single crystals of Cu3BHT with high crystallinity, revealing a quasi-two-dimensional kagome structure with non-van der Waals interlayer Cu-S covalent bonds. These crystals exhibit intrinsic metallic behavior, with conductivity reaching 103 S/cm at 300 K and 104 S/cm at 2 K. Notably, superconductivity in Cu3BHT crystals is observed at 0.25 K, attributed to enhanced electron-electron interactions and electron-phonon coupling in the non-van der Waals structure. The discovery of this clear correlation between atomic-level crystal structure and electrical properties provides a crucial foundation for advancing superconductor coordination polymers, with potential to revolutionize future quantum devices.

Designed functions of oxide/hydroxide nanosheets via elemental replacement/doping

Partial replacement of one structural element in a solid with another of a similar size was conducted to impart functionality to the solids and modify their properties. This phenomenon is found in nature in coloured gemstones and clay minerals and is used in materials chemistry and physics, endowing materials with useful properties that can be controlled by incorporated heteroelements and their amounts. Depending on the area of research (or expected functions), the replacement is referred to as "isomorphous substitution", "doping", etc. Herein, elemental replacement in two-dimensional (2D) oxides and hydroxides (nanosheets or layered materials) is summarised with emphasis on the uniqueness of their preparation, characterisation and application compared with those of the corresponding bulk materials. Among the 2D materials (graphene, metallenes, transition metal chalcogenides, metal phosphate/phosphonates, MXenes, etc.), 2D oxides and hydroxides are characterised by their presence in nature, facile synthesis and storage under ambient conditions, and possible structural variation from atomic-level nanosheets to thicker nanosheets composed of multilayered structures. The heteroelements to be doped were selected depending on the target application objectively; however, there are structural and synthetic limitations in the doping of heteroelements. In the case of layered double hydroxides (single layer) and layered alkali silicates (from single layer to multiple layers), including layered clay minerals (2 : 1 layer), the replacement (commonly called isomorphous substitution) is discussed to understand/design characteristics such as catalytic, adsorptive (including ion exchange), and swelling properties. Due to the variation in their main components, the design of layered transition metal oxide/hydroxide materials via isomorphous substitution is more versatile; in this case, tuning their band structure, doping both holes and electrons, and creating impurity levels are examined by the elemental replacement of the main components. As typical examples, material design for the photocatalytic function of an ion-exchangeable layered titanate (lepidocrocite-type titanate) and a perovskite niobate (KCa2Nb3O10) is discussed, where elemental replacement is effective in designing their multiple functions.

Electronic, optical and charge transport properties of Zn-porphyrin-C60 MOFs: a combined periodic and cluster modeling

Density functional theory (DFT) calculations were performed on the 5,15 meso-positions of nine porphyrin-containing MOFs; Zn2(TCPB)-(NMe2-ZnP); (H4TCPB = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene), (NMe2-ZnP = [5,15-bis[(4-pyridyl)-ethynyl]-10,20-bis-(dimethylamine) porphinato]zinc(II)) functionalized with nitrogen-, oxygen-, and sulfur-containing groups to study their effects on the electronic, optical and transport properties of the materials. The properties of these materials have also been investigated by encapsulating fullerene (C60) in their pores (C60@MOFs). The results indicate that the guest C60 in the MOF generates high photoconductivity through efficient porphyrin/fullerene donor-acceptor (D-A) interactions, which are facilitated by oxygen and sulfur functionalities. DFT calculations show that C60 interacts favorably in MOFs due to negative Eint values. Encapsulated C60 molecules modify the electronic band structure, affecting the conduction band and unoccupied states of MOFs corresponding to C60 p orbitals. TD-DFT calculations show that incorporating C60 promotes D-A interactions in MOFs, leading to charge transfer in the near-infrared and visible photoinduced electron transfer (PET) from porphyrins to C60. Nonequilibrium Green's function-based calculations for MOFs with sulfur group, with and without C60, performed using molecular junctions with Au(111)-based electrodes show increased charge transport for the doped MOF. These insights into tuning electronic/optical properties and controlling charge transfer can aid in the design of new visible/near-infrared MOF-based optoelectronic devices.