Ultrabroadband plasmon driving selective photoreforming of methanol under ambient conditions.

Liquid methanol has the potential to be the hydrogen energy carrier and storage medium for the future green economy. However, there are still many challenges before zero-emission, affordable molecular H2 can be extracted from methanol with high performance. Here, we present noble-metal-free Cu-WC/W plasmonic nanohybrids which exhibit unsurpassed solar H2 extraction efficiency from pure methanol of 2,176.7 µmol g-1 h-1 at room temperature and normal pressure. Macro-to-micro experiments and simulations unveil that local reaction microenvironments are generated by the coperturbation of WC/W's lattice strain and infrared-plasmonic electric field. It enables spontaneous but selective zero-emission reaction pathways. Such microenvironments are found to be highly cooperative with solar-broadband-plasmon-excited charge carriers flowing from Cu to WC surfaces for efficient stable CH3OH plasmonic reforming with C3-dominated liquid products and 100% selective gaseous H2. Such high efficiency, without any COx emission, can be sustained for over a thousand-hour operation without obvious degradation.

Self-Sorting of Interfacial Compatibility in MOF-Based Mixed Matrix Membranes.

Metal-organic framework (MOF)-based mixed matrix membranes (MMMs) have shown great promises to overcome the performance upper limit of polymeric membranes for various gas separation processes. However, the gas separation properties of the MMMs largely depend on the MOF-polymer interfacial compatibility which is a metric difficult to quantify. In most cases, whether a MOF filler and a polymer matrix make a good pair is not revealed until the gas transport experiments are performed. This is because there is a lack of characterization techniques to directly probe the MOF-polymer interfacial compatibility. In this work, we demonstrate a self-sorting method to rank the interface compatibility among several MOF-polymer pairs. By mixing one MOF with two polymers in an MMM, the demixing of two polymers will form two polymer domains. The MOF particles will preferably partition into the "preferred" polymer domain due to their higher interfacial affinity. By scanning different polymer pairs, a rank of MOF-polymer interfacial compatibility from high to low can be obtained. Moreover, based on this ranking, it was also found that a highly compatible MOF-polymer pair suggested by this method also corresponds to a more predictable MMM gas separation performance.

Atomic-Scale Elucidation of Unusually Distorted Dimeric Complexes Confined in a Zr-Based Metal-Organic Framework.

Nanoconfinement in metal-organic framework (MOF) pores can lead to the isolation of unusual or reactive metal complexes. However, MOFs that support the stabilization and precise structural elucidation of metal complexes and small metal clusters are rare. Here, we report a thermally and chemically stable zirconium-based MOF (University of Adelaide Material-1001, UAM-1001) with a high density of free bis-pyrazolyl units that can confine mono- and dinuclear metal complexes. The precursor MOF, UAM-1000, has a high degree of structural flexibility, but post synthetic modification with a bracing linker, biphenyl-4,4'-dicarboxylic acid, partially rigidifies the MOF (UAM-1001). This allows "matrix isolation" and detailed structural elucidation of postsynthetically added dimeric complexes bound within a tetradentate binding site formed by two linkers. Dimeric species [Co2Cl4], [Cu2Cl4], [Ni2Cl3(H2O)2]Cl, and [Rh2(CO)3Cl2] were successfully isolated in UAM-1001 and characterized by single-crystal X-ray diffraction. Comparison of the UAM-1001 isolated species with similar complexes in the solid state reveals that UAM-1001 can significantly distort the structures and enforce notably shorter metal-metal distances. For example, MOF tethering allows isolation of a [Cu2Cl4] complex that rapidly reacts with water in the solid state. The stability, porosity, and modulated flexibility of UAM-1001 provide an ideal platform material for the isolation and study of new dimeric complexes and their reactivity.

A Lantern-Shaped Pd(II) Cage Constructed from Four Different Low-Symmetry Ligands with Positional and Orientational Control: An Ancillary Pairings Approach.

One of the key challenges of metallo-supramolecular chemistry is to maintain the ease of self-assembly but, at the same time, create structures of increasingly high levels of complexity. In palladium(II) quadruply stranded lantern-shaped cages, this has been achieved through either 1) the formation of heteroleptic (multi-ligand) assemblies, or 2) homoleptic assemblies from low-symmetry ligands. Heteroleptic cages formed from low-symmetry ligands, a hybid of these two approaches, would add an additional rich level of complexity but no examples of these have been reported. Here we use a system of ancillary complementary ligand pairings at the termini of cage ligands to target heteroleptic assemblies: these complementary pairs can only interact (through coordination to a single Pd(II) metal ion) between ligands in a cis position on the cage. Complementarity between each pair (and orthogonality to other pairs) is controlled by denticity (tridentate to monodentate or bidentate to bidentate) and/or hydrogen-bonding capability (AA to DD or AD to DA). This allows positional and orientational control over ligands with different ancillary sites. By using this approach, we have successfully used low-symmetry ligands to synthesise complex heteroleptic cages, including an example with four different low-symmetry ligands.

Temperature Driven Transformation of the Flexible Metal-Organic Framework DUT-8(Ni).

DUT-8(Ni) metal-organic framework (MOF) belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT-8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to a new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X-ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition.

A Switchable Palladium(II) Trefoil Entangled Tetrahedron with Temperature Dependence and Concentration Independence.

Self-assembly makes metallo-interlocked architectures attractive targets, but being in equilibrium with smaller species means that they can suffer from dilution effects. We show that a junctioned system gives rise to a [Pd4 (L)2 ]8+ trefoil entangled tetrahedron irrespective of concentration. Heating the sample reversibly shifts the equilibrium from the knot to an isomeric non-interlocked dual metallo-cycle, demonstrating that thermodynamic equilibria can still be exploited for switching even in the absence of concentration effects.

Charting the Complete Thermodynamic Landscape of Gas Adsorption for a Responsive Metal-Organic Framework.

New nanoporous materials have the ability to revolutionize adsorption and separation processes. In particular, materials with adaptive cavities have high selectivity and may display previously undiscovered phenomena, such as negative gas adsorption (NGA), in which gas is released from the framework upon an increase in pressure. Although the thermodynamic driving force behind this and many other counterintuitive adsorption phenomena have been thoroughly investigated in recent years, several experimental observations remain difficult to explain. This necessitates a comprehensive analysis of gas adsorption akin to the conformational free energy landscapes used to understand the function of proteins. We have constructed the complete thermodynamic landscape of methane adsorption on DUT-49. Traversing this complex landscape reproduces the experimentally observed structural transitions, temperature dependence, and the hysteresis between adsorption and desorption. The complete thermodynamic description presented here provides unparalleled insight into adsorption and provides a framework to understand other adsorbents that challenge our preconceptions.

Unraveling the Guest-Induced Switchability in the Metal-Organic Framework DUT-13(Zn)*.

The switching mechanism of the flexible framework Zn4 O(benztb)1.5 (benztb=N,N,N',N'-benzidine tetrabenzoate), also known as DUT-13, was studied by advanced powder X-ray diffraction (PXRD) and gas physisorption techniques. In situ synchrotron PXRD experiments upon physisorption of nitrogen (77 K) and n-butane (273 K) shed light on the hitherto unnoticed guest-induced breathing in the MOF. The mechanism of contraction is based on the conformationally labile benztb ligand and accompanied by a reduction in specific pore volume from 2.03 cm3 g-1 in the open-pore phase to 0.91 cm3 g-1 in the contracted-pore phase. The high temperature limit for adsorption-induced contraction of 170 K, determined by systematic temperature variation of methane adsorption isotherms, indicates that the DUT-13 framework is softer than other mesoporous MOFs like DUT-49 and does not support the formation of overloaded metastable states required for negative gas-adsorption transitions.

A Universal Standard Archive File for Adsorption Data.

New advanced adsorbents are a crucial driver for the development of energy and environmental applications. Tremendous potential is provided by machine learning and data mining techniques, as these approaches can identify the most appropriate adsorbent for a particular application. However, the current scientific reporting of adsorption isotherms in graphs and figures is not adequate to reproduce original experimentally measured data. This report proposes the specification of a new standard adsorption information file (AIF) inspired by the ubiquitous crystallographic information file (CIF) and based on the self-defining text archive and retrieval (STAR) procedure, also used to represent biological nuclear magnetic resonance experiments (NMR-STAR). The AIF is a flexible and easily extended free-format archive file that is readily human and machine readable and is simple to edit using a basic text editor or parse for database curation. This format represents the first steps toward an open adsorption data format as a basis for a decentralized adsorption data library. An open format facilitates the electronic transmission of adsorption data between laboratories, journals, and larger databases, which is key in the effort to increase open science in the field of porous materials in the future.

Cooperative and synchronized rotation in motorized porous frameworks: impact on local and global transport properties of confined fluids.

Molecules in gas and liquid states, as well as in solution, exhibit significant and random Brownian motion. Molecules in the solid-state, although strongly immobilized, can still exhibit significant intramolecular dynamics. However, in most framework materials, these intramolecular dynamics are driven by temperature, and therefore are neither controlled nor spatially or temporarily aligned. In recent years, several examples of molecular machines that allow for a stimuli-responsive control of dynamical motion, such as rotation, have been reported. In this contribution, we investigate the local and global properties of a Lennard-Jones (LJ) fluid surrounding a molecular motor and consider the influence of cooperative and non-directional rotation for a molecular motor-containing pore system. This study uses classical molecular dynamics simulations to describe a minimal model, which was developed to resemble known molecular motors. The properties of an LJ liquid surrounding an isolated molecular motor remain mostly unaffected by the introduced rotation. We then considered an arrangement of motors within a one-dimensional pore. Changes in diffusivity for pore sizes approaching the length of the rotor were observed, resulting from rotation of the motors. We also considered the influence of cooperative motor directionality on the directional transport properties of this confined fluid. Importantly, we discovered that specific unidirectional rotation of altitudinal motors can produce directed diffusion. This study provides an essential insight into molecular machine-containing frameworks, highlighting the specific structural arrangements that can produce directional mass transport.

The role of temperature and adsorbate on negative gas adsorption transitions of the mesoporous metal-organic framework DUT-49.

Unusual adsorption phenomena, such as breathing and negative gas adsorption (NGA), are rare and challenge our thermodynamic understanding of adsorption in deformable porous solids. In particular, NGA appears to break the rules of thermodynamics in these materials by exhibiting a spontaneous release of gas accompanying an increase in pressure. This anomaly relies on long-lived metastable states. A fundamental understanding of this process is desperately required for the discovery of new materials with this exotic property. Interestingly, NGA was initially observed upon adsorption of methane at relatively low temperature, close to the respective standard boiling point of the adsorptive, and no NGA was observed at elevated temperatures. In this contribution, we present an extensive investigation of adsorption of an array of gases at various temperatures on DUT-49, a material which features an NGA transition. Experiments, featuring a wide range of gases and vapors at temperatures ranging from 21-308 K, were used to identify for each guest a critical temperature range in which NGA can be detected. The experimental results were complemented by molecular simulations that help to rationalize the absence of NGA at elevated temperatures, and the non-monotonic behavior present upon temperature decrease. Furthermore, this in-depth analysis highlights the crucial thermodynamic and kinetic conditions for NGA, which are unique to each guest and potentially other solids with similar effects. We expect this exploration to provide detailed guidelines for experimentally discovering NGA and related "rule breaking" phenomena in novel and already known materials, and provide the conditions required for the application of this effect, for example as pressure amplifying materials.

MOF matrix isolation: cooperative conformational mobility enables reliable single crystal transformations.

Obtaining structural information for highly reactive metal-based species can provide valuable insight into important chemical transformations or catalytic processes. Trapping these metal-based species within the cavities of porous crystalline hosts, such as metal-organic frameworks (MOFs), can stabilise them, allowing detailed structural elucidation by single crystal X-ray diffraction. Previously, we have used a bespoke flexible MOF, [Mn3L2L'] (MnMOF-1, where L = bis-(4-carboxyphenyl-3,5-dimethylpyrazolyl)methane and L = L', but L' has a vacant N,N'-chelation site), which has a chelating site capable of post-synthetically binding metal ions, to study organometallic transformations and fundamental isomerisation processes. This manuscript will report the underlying conformational flexibility of the framework, demonstrate the solvent dependency of post-synthetic metalation, and show that the structural flexibility of the linker site and framework are critical to controlling and achieving high levels of metal loading (and therefore site occupancy) during chemical transformations. From these results, a set of design principles for linker-based "matrix isolation" and structure determination in MOFs are derived.

Highly Active Gas Phase Organometallic Catalysis Supported Within Metal-Organic Framework Pores.

Metal-organic frameworks (MOFs) can act as a platform for the heterogenization of molecular catalysts, providing improved stability, allowing easy catalyst recovery and a route toward structural elucidation of the active catalyst. We have developed a MOF, 1, possessing vacant N,N-chelating sites which are accessible via the porous channels that penetrate the structure. In the present work, cationic rhodium(I) norbornadiene (NBD) and bis(ethylene) (ETH) complexes paired with both noncoordinating and coordinating anions have been incorporated into the N,N-chelation sites of 1 via postsynthetic metalation and facile anion exchange. Exploiting the crystallinity of the host framework, the immobilized Rh(I) complexes were structurally characterized using X-ray crystallography. Ethylene hydrogenation catalysis by 1·[Rh(NBD)]X and 1·[Rh(ETH)2]X (X = Cl and BF4) was studied in the gas phase (2 bar, 46 °C) to reveal that 1·[Rh(ETH)2](BF4) was the most active catalyst (TOF = 64 h-1); the NBD materials and the chloride salt were notably less active. On the basis of these observations, the activity of the Rh(I) bis(ethylene) complexes, 1·[Rh(ETH)2]BF4 and 1·[Rh(ETH)2]Cl, in butene isomerization was also studied using gas-phase NMR spectroscopy. Under one bar of butene at 46 °C, 1·[Rh(ETH)2]BF4 rapidly catalyzes the conversion of 1-butene to 2-butene with a TOF averaging 2000 h-1 over five cycles. Notably, the chloride derivative, 1 [Rh(ETH)2]Cl displays negligible activity in comparison. XPS analysis of the postcatalysis sample, supported by DFT calculations, suggest that the catalytic activity is inhibited by the strong interactions between a Rh(III) allyl hydride intermediate and the chloride anion.

Direct Mechanocatalysis: Palladium as Milling Media and Catalyst in the Mechanochemical Suzuki Polymerization.

The milling ball is the catalyst. We introduce a palladium-catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium-catalyzed C-C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4-bromo or 4-iodophenylboronic acid giving poly(para-phenylene). Surprisingly, we observe one of the highest degrees of polymerization (199) reported so far.

Application of computational methods to the design and characterisation of porous molecular materials.

Composed from discrete units, porous molecular materials (PMMs) possess unique properties not observed for conventional, extended, solids, such as solution processibility and permanent porosity in the liquid phase. However, identifying the origin of porosity is not a trivial process, especially for amorphous or liquid phases. Furthermore, the assembly of molecular components is typically governed by a subtle balance of weak intermolecular forces that makes structure prediction challenging. Accordingly, in this review we canvass the crucial role of molecular simulations in the characterisation and design of PMMs. We will outline strategies for modelling porosity in crystalline, amorphous and liquid phases and also describe the state-of-the-art methods used for high-throughput screening of large datasets to identify materials that exhibit novel performance characteristics.

Balancing Mechanical Stability and Ultrahigh Porosity in Crystalline Framework Materials.

A new mesoporous metal-organic framework (MOF; DUT-60) was conceptually designed in silico using Zn4 O6+ nodes, ditopic and tritopic linkers to explore the stability limits of framework architectures with ultrahigh porosity. The robust ith-d topology of DUT-60 provides an average bulk and shear modulus (4.97 GPa and 0.50 GPa, respectively) for this ultra-porous framework, a key prerequisite to suppress pore collapse during desolvation. Subsequently, a cluster precursor approach, resulting in minimal side product formation in the solvothermal synthesis, was used to produce DUT-60, a new crystalline framework with the highest recorded accessible pore volume (5.02 cm3 g-1 ) surpassing all known crystalline framework materials.

Microscopic Mechanism of Chiral Induction in a Metal-Organic Framework.

The recently reported process of chiral induction in a metal-organic framework (MOF) by nonchiral guest adsorption, demonstrated on the prototypical MOF-5, may revolutionize the production of MOFs for enantioselective separation and catalysis. Herein, we describe an investigation employing multiscale molecular simulation to discover the microscopic mechanism of chiral induction and investigate the stability of the resulting framework. Our results explain how the molecular size and chemical nature of N-methyl-2-pyrrolidone (NMP) give rise to the chiral transformation in MOF-5, whereas it cannot occur for other guest molecules, such as N,N-dimethylformamide (DMF). Moreover, we show that the guest-free CMOF-5 structure is energetically unstable, with either the achiral conventional structure or a closed pore structure preferred, demonstrating that chirality will not be retained upon activation of CMOF-5. While this limits the usability of chiral induction in MOFs, our study opens new avenues for the use of other guest molecules and provides microscopic insight into this unexpected outcome of guest-framework interactions in a soft porous crystal.

Post-synthetic metalation of metal-organic frameworks.

Post-synthetic metalation (PSMet) offers expansive scope for a targeted approach to tailoring the properties of MOFs. Numerous methods for carrying-out PSMet chemistry have been reported, however, these can be categorized into three general strategies: (a) addition to coordinating groups; (b) counter-ion exchange in charged frameworks; or, (c) host-guest encapsulation of metal-containing entities within the pores of the framework. PSMet has been applied to enhance the performance characteristics of parent MOFs for gas storage and separation, and catalysis. Notably, PSMet is a prominent strategy in the field of MOF catalysis as it offers a route to design size-selective catalysts, based on the premise of reticular chemistry in MOFs and the ability to incorporate a range of catalytically-active metal centres. Other applications for materials produced via or utilising PSMet strategies include enhancing gas storage or molecular separations, the triggered release of drugs, sensing and tunable light emission for luminescent materials. This review surveys seminal examples of PSMet to highlight the broad scope of this technique for enhancing the performance characteristics of MOFs and to demonstrate how the PSMet concept can be developed for future applications.

The use of collective variables and enhanced sampling in the simulations of existing and emerging microporous materials.

Microporous materials, including zeolites, metal-organic frameworks, and cage compounds, offer diverse functionalities due to their unique dynamics and guest confinement properties. These materials play a significant role in separation, catalysis, and sensing, but their complexity hinders exploration using traditional atomistic simulations. This review explores collective variables (CVs) paired with enhanced sampling as a powerful approach to enable efficient investigation of key features in microporous materials. We highlight successful applications of CVs in studying adsorption, diffusion, phase transitions, and mechanical properties, demonstrating their crucial role in guiding material design and optimisation. The future of CVs lies in integration with techniques like machine learning, allowing for enhanced efficiency and accuracy. By tailoring CVs to specific materials and developing multi-scale approaches we can further unlock the intricacies of these fascinating materials. Simulations are a cornerstone in unravelling the complexities of microporous materials and are crucial for our future understanding.