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Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. As a representative system, water-filled carbon nanotubes (CNTs) are generally studied, but direct observation of the crystal structure and proton transport is difficult for CNTs due to their poor crystallinity and high electron conduction. Here, we report the direct observation of a unique water-cluster structure and high proton conduction realized in a metal-organic nanotube, [Pt(dach)(bpy)Br] 4 (SO 4 ) 4 ·32H 2 O (dach: (1R, 2R)-(–)-1,2-diaminocyclohexane; bpy: 4,4’-bipyridine). In the crystalline state, a hydrogen-bonded ice nanotube composed of water tetramers and octamers is found within the hydrophobic nanochannel. Single-crystal impedance measurements along the channel direction reveal a high proton conduction of 10 −2 Scm −1 . Moreover, fast proton diffusion and continuous liquid-to-solid transition are confirmed using solid-state 1 H-NMR measurements. Our study provides valuable insight into the structural and dynamical properties of confined water within 1D hydrophobic nanochannels. Water confined in natural or synthetic hydrophobic nano-spaces behaves differently than in the bulk. Here the authors investigate water in hydrophobic synthetic 1D nanochannels revealing water clustering in tetramers and octamers and high proton conductivity, along with a continuous liquid to solid transition.

The safe storage of flammable gases, such as acetylene, is essential for current industrial purposes. However, the narrow pressure ( P ) and temperature range required for the industrial use of pure acetylene (100 <  P  < 200 kPa at 298 K) and its explosive behaviour at higher pressures make its storage and release challenging. Flexible metal–organic frameworks that exhibit a gated adsorption/desorption behaviour—in which guest uptake and release occur above threshold pressures, usually accompanied by framework deformations—have shown promise as storage adsorbents. Herein, the pressures for gas uptake and release of a series of zinc-based mixed-ligand catenated metal–organic frameworks were controlled by decorating its ligands with two different functional groups and changing their ratio. This affects the deformation energy of the framework, which in turn controls the gated behaviour. The materials offer good performances for acetylene storage with a usable capacity of ~90 v/v (77% of the overall amount) at 298 K and under a practical pressure range (100–150 kPa). Flexible metal–organic frameworks (MOFs) in which guest uptake and release occur above certain threshold pressures are attractive adsorbents. Now, the gated sorption behaviour of such a zinc-based mixed-ligand MOF has been tuned to match the narrow temperature and pressure range required for safe, efficient acetylene storage by adjusting the ratio of two different functional groups on its benzenedicarboxylate ligands.

Functional nanomaterials with enzyme-mimicking activities, termed as nanozymes, have found wide applications in various fields. However, the deviation between the working and optimal pHs of nanozymes has been limiting their practical applications. Here we develop a strategy to modulate the microenvironmental pHs of metal–organic framework (MOF) nanozymes by confining polyacids or polybases (serving as Brønsted acids or bases). The confinement of poly(acrylic acid) (PAA) into the channels of peroxidase-mimicking PCN-222-Fe (PCN = porous coordination network) nanozyme lowers its microenvironmental pH, enabling it to perform its best activity at pH 7.4 and to solve pH mismatch in cascade systems coupled with acid-denatured oxidases. Experimental investigations and molecular dynamics simulations reveal that PAA not only donates protons but also holds protons through the salt bridges between hydroniums and deprotonated carboxyl groups in neutral pH condition. Therefore, the confinement of poly(ethylene imine) increases the microenvironmental pH, leading to the enhanced hydrolase-mimicking activity of MOF nanozymes. This strategy is expected to pave a promising way for designing high-performance nanozymes and nanocatalysts for practical applications. NCOMMS-24-44031B Nanozymes have found wide applications in various fields, but the deviation between the working and optimal pHs of nanozymes limits their practical applications. Here, the authors report a strategy to modulate the microenvironmental pHs of metal–organic framework nanozymes, enabling them to exhibit optimal activity under neutral pH conditions.

Over the long history of evolution, nature has developed a variety of biological systems with switchable recognition functions, such as the ion transmissibility of biological membranes, which can switch their ion selectivities in response to diverse stimuli. However, developing a method in an artificial host-guest system for switchable recognition of specific guests upon the change of external stimuli is a fundamental challenge in chemistry because the order in the host-guest affinity of a given system hardly varies along with environmental conditions. Herein, we report temperature-responsive recognition of two similar gaseous guests, CO 2 and C 2 H 2 , with selectivities switched by temperature change by a diffusion-regulatory mechanism, which is realized by a dynamic porous crystal featuring ultrasmall pore apertures with flip-flop locally-motive organic moiety. The dynamic local motion regulates the diffusion process of CO 2 and C 2 H 2 and amplifies their rate differences, allowing the crystal to selectively adsorb CO 2 at low temperatures and C 2 H 2 at high temperatures with separation factors of 498 (CO 2 /C 2 H 2 ) and 181 (C 2 H 2 /CO 2 ), respectively. The design of host-guest systems for switchable recognition of guests upon the change of external stimuli is challenging due to the invariable host-guest affinity. Here, the authors encode a dynamic motion into a porous crystal to regulate the diffusion of CO2 and C2H2 allowing the crystal to switch the gas recognition selectivity by temperature.

Selective molecular recognition is an important alternative to the energy-intensive industrial separation process. Porous coordination polymers (PCPs) offer designing platforms for gas separation because they possess precise controllability over structures at the molecular level. However, PCPs-based gas separations are dominantly achieved using strong adsorptive sites for thermodynamic recognition or pore-aperture control for size sieving, which suffer from insufficient selectivity or sluggish kinetics. Developing PCPs that work at high temperatures and feature both high uptake capacity and selectivity is urgently required but remains challenging. Herein, we report diffusion-rate sieving of propylene/propane (C 3 H 6 /C 3 H 8 ) at 300 K by constructing a PCP material whose global and local dynamics cooperatively govern the adsorption process via the mechanisms of the gate opening for C 3 H 6 and the diffusion regulation for C 3 H 8 , respectively, yielding substantial differences in both uptake capacity and adsorption kinetics. Dynamic separation of an equimolar C 3 H 6 /C 3 H 8 mixture reveals outstanding sieving performance with a C 3 H 6 purity of 99.7% and a separation factor of 318. Porous coordination polymers (PCPs) are commonly used in gas separation processes but developing PCPs that work at high temperatures and feature both high uptake capacity and selectivity remains challenging. Here, the authors report diffusion-rate sieving of propylene/propane at 300 K by constructing a PCP whose global and local dynamics cooperatively govern the adsorption process via gate opening for propylene and diffusion regulation for propane.

Direct structural information of confined CO 2 in a micropore is important for elucidating its specific binding or activation mechanism. However, weak gas-binding ability and/or poor sample crystallinity after guest exchange hindered the development of efficient materials for CO 2 incorporation, activation and conversion. Here, we present a dynamic porous coordination polymer (PCP) material with local flexibility, in which the propeller-like ligands rotate to permit CO 2 trapping. This process can be characterized by X-ray structural analysis. Owing to its high affinity towards CO 2 and the confinement effect, the PCP exhibits high catalytic activity, rapid transformation dynamics, even high size selectivity to different substrates. Together with an excellent stability with turnover numbers (TON) of up to 39,000 per Zn 1.5 cluster of catalyst after 10 cycles for CO 2 cycloaddition to form value-added cyclic carbonates, these results demonstrate that such distinctive structure is responsible for visual CO 2 capture and size-selective conversion. Porous coordination polymers that possess structural flexibility show great promise for gas adsorption and catalysis. Here the authors synthesize a dynamic porous coordination polymer with rotating ligands that permit effective CO 2 trapping, and demonstrate subsequent CO 2 cycloaddition to epoxides.

Developing artificial porous systems with high molecular recognition performance is critical but very challenging to achieve selective uptake of a particular component from a mixture of many similar species, regardless of the size and affinity of these competing species. A porous platform that integrates multiple recognition mechanisms working cooperatively for highly efficient guest identification is desired. Here, we designed a flexible porous coordination polymer (PCP) and realised a corrugated channel system that cooperatively responds to only target gas molecules by taking advantage of its stereochemical shape, location of binding sites, and structural softness. The binding sites and structural deformation act synergistically, exhibiting exclusive discrimination gating (EDG) effect for selective gate-opening adsorption of CO 2 over nine similar gas molecules, including N 2 , CH 4 , CO, O 2 , H 2 , Ar, C 2 H 6 , and even higher-affinity gases such as C 2 H 2 and C 2 H 4 . Combining in-situ crystallographic experiments with theoretical studies, it is clear that this unparalleled ability to decipher the CO 2 molecule is achieved through the coordination of framework dynamics, guest diffusion, and interaction energetics. Furthermore, the gas co-adsorption and breakthrough separation performance render the obtained PCP an efficient adsorbent for CO 2 capture from various gas mixtures. Developing porous systems with high molecular recognition performance can be challenging. Here the authors present a corrugated channel system that cooperatively responds to only CO 2 molecules over nine other similar gas molecules.

The discovery of a method to separate isotopologues, molecular entities that differ in only isotopic composition 1 , is fundamentally and technologically essential but remains challenging 2 , 3 . Water isotopologues, which are very important in biological processes, industry, medical care, etc. are among the most difficult isotopologue pairs to separate because of their very similar physicochemical properties and chemical exchange equilibrium. Herein, we report efficient separation of water isotopologues at room temperature by constructing two porous coordination polymers (PCPs, or metal–organic frameworks) in which flip-flop molecular motions within the frameworks provide diffusion-regulatory functionality. Guest traffic is regulated by the local motions of dynamic gates on contracted pore apertures, thereby amplifying the slight differences in the diffusion rates of water isotopologues. Significant temperature-responsive adsorption occurs on both PCPs: H 2 O vapour is preferentially adsorbed into the PCPs, with substantially increased uptake compared to that of D 2 O vapour, facilitating kinetics-based vapour separation of H 2 O/HDO/D 2 O ternary mixtures with high H 2 O separation factors of around 210 at room temperature. The authors demonstrate efficient separation of water isotopologues at room temperature using two porous coordination polymers that amplify their diffusion-rate difference.

Sustainable ammonia synthesis, a key focus in electrochemistry, has seen significant advancements with the emergence of Metal‐Organic Frameworks (MOFs). This review provides a comprehensive analysis of the recent strides in MOF‐based materials for green ammonia production, reflecting the urgency to develop eco‐friendly and energy‐efficient chemical commodities. It explores the reaction mechanisms, emphasizing the importance of structure‐performance relationships in MOF optimization and the design of MOF‐based electrocatalysts, including metal node engineering and hybrid materials. The review also highlights in‐situ characterization techniques that are crucial for understanding MOF catalytic activity. It establishes a correlation between MOF features, synthesis methods, and material performance, showcasing their potential in catalysis. Finally, it identifies challenges and future directions for MOFs in green ammonia production, aiming to inspire innovation towards sustainable and economically viable processes. Sustainable ammonia synthesis, crucial in electrochemistry, advances with metal‐organic frameworks (MOFs). The review examines MOF materials for eco‐friendly ammonia, stressing structure‐performance ties in MOF optimization and electrocatalyst design. It underscores in‐situ techniques for catalytic activity, linking MOF attributes to synthesis and performance, and pinpoints challenges for sustainable, cost‐effective ammonia production. Note: MOFs, Metal‐Organic Frameworks.

Reactions of the ternary components of Co2+ ion, 4,4′-bipyridine, and NO3− give several coordination polymers, which are often obtained in mixed phases. Herein, we explore the condition for the selective formation of Co-1D chain and Co-tongue-and-groove coordination polymers and find reversible interconversion pathways between them. The crystal structures of Co-tongue-and-groove in desolvated and two different CO2-adsorbed states show a one-dimensional corrugated channel with small windows through which CO2 is unlikely to pass. Nevertheless, a sufficient amount of CO2 is adsorbed at 195 K. The CO2 molecules are accommodated in the swollen cavity, forcing their way through the seemingly impermeable window of the channel, which we have named squeezing adsorption. The local motion of the ligand of the window frame plays an essential role in the guest permeation, which proves that the tongue-and-groove coordination polymers are essentially locally flexible porous frameworks.Mixed-phase coordination polymers are often formed when using ternary components. Here, conditions for the selective formation of [Co2(4,4′-bpy)3(NO3)4] are deduced, which shows unique gas adsorption squeezing through seemingly impassable narrow windows due to local structural flexibility.