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The synthesis of three-dimensional (3D) covalent organic frameworks (COFs) requires high-connectivity polyhedral building blocks or the controlled alignment of building blocks. Here, we use the latter strategy to assemble square-planar cobalt(II) phthalocyanine (PcCo) units into the nbo topology by using tetrahedral spiroborate (SPB) linkages that were chosen to provide the necessary 90° dihedral angles between neighboring PcCo units. This yields a porous 3D COF, SPB-COF-DBA, with a noninterpenetrated nbo topology. SPB-COF-DBA shows high crystallinity and long-range order, with 11 resolved diffraction peaks in the experimental powder X-ray diffraction (PXRD) pattern. This well-ordered crystal lattice can also be imaged by using high-resolution transmission electron microscopy (HR-TEM). SPB-COF-DBA has cubic pores and exhibits permanent porosity with a Brunauer-Emmett-Teller (BET) surface area of 1726 m2 g-1.

Ethyl acetate is an important chemical raw material and solvent. It is also a key volatile organic compound in the brewing industry and a marker for lung cancer. Materials that are highly selective toward ethyl acetate are needed for its separation and detection. Here, we report a trianglimine macrocycle (TAMC) that selectively adsorbs ethyl acetate by forming a solvate. Crystal structure prediction showed this to be the lowest energy solvate structure available. This solvate leaves a metastable, “templated” cavity after solvent removal. Adsorption and breakthrough experiments confirmed that TAMC has adequate adsorption kinetics to separate ethyl acetate from azeotropic mixtures with ethanol, which is a challenging and energy‐intensive industrial separation., The separation of ethyl acetate from its azeotropic mixtures with ethanol is of great importance in the industrial production of ethyl acetate. Current purification techniques include extractive distillation and azeotropic distillation are energy‐intensive. Guided by crystal structure prediction, a “templating” strategy was used to construct selective binding sites in a trianglimine macrocycle crystal for the solvent molecule. These crystals exhibit inherently high selectivity towards ethyl acetate, reasonable kinetics, and show promise for real‐life, practical dynamic separations.

Mercury pollution is a significant threat to the environment and health worldwide. Therefore, effective and low-cost absorbents that are easily scalable are needed for real-world applications. Enlarging the surface area of the materials and doping with heteroatoms are two of the most common strategies to cope with this problem. Sulfur-doped activated carbon synthesized from the carbonization of inverse vulcanized thiopolymers makes it possible to combine both large specific surface area and doping of heteroatoms, resulting in outperformance in mercury uptake against commercial activated carbons. Convenient recovery of mercury absorbents after treatment should be beneficial in mercury collecting and recycling. Therefore, magnetic sulfur-doped carbons (MSCs) were prepared by functionalizing sulfur doped carbons through chemical precipitation with magnetic iron oxides. Besides the characterisations of materials, mercury uptake experiments, such as stactic test, capacity test, impact of solution pH, and mixed ions interferences were performed. These MSCs exhibit high specific surface area (1,329 m2/g), high sulfur content (up to 14.8 wt%), porous structure, low cost, and are convenient for retrieval. MSCs are demonstrated high uptake capacity (187 mg g-1) and efficiency in mercury solution and multifunctional absorption in mixed ions solution, showing their potential to be applied in water purification and environmental remediation.

Covalent organic framework nanosheets (CONs), fabricated from twodimensional covalent organic frameworks (COFs), present a promising strategy for incorporating atomically distributed catalytic metal centers into well-defined pore structures with desirable chemical environments. Here, a series of CONs was synthesized by embedding single cobalt sites that were then evaluated for photocatalytic carbon dioxide reduction. A partially fluorinated, cobalt-loaded CON produced 10.1 μmol carbon monoxide with a selectivity of 76%, over 6 hours irradiation under visible light (TON = 28.1), and a high external quantum efficiency (EQE) of 6.6% under 420 nm irradiation in the presence of an iridium dye. The CONs appear to act as a semiconducting support, facilitating charge carrier transfer between the dye and the cobalt centers, and this results in a performance comparable with that of the state-of-the-art heterogeneous catalysts in the literature under similar conditions. The ultrathin CONs outperformed their bulk counterparts in all cases, suggesting a general strategy to enhance the photocatalytic activities of COF materials.

The development of robust synthetic routes to stable covalent organic frameworks (COFs) is important to broaden the range of applications for these materials. We report here a simple and efficient three-component assembly reaction between readily available aldehydes, amines, and elemental sulfur via a C-H functionalization and oxidative annulation under transition-metal-free conditions. Five thiazole-linked COFs (TZ-COFs) were synthesized using this method. These materials showed high levels of crystallinity, high specific surface areas, and excellent physicochemical stability. The photocatalytic applications of TZ-COFs were investigated, and TZ-COF-4 gave high sacrificial hydrogen evolution rates from water (up to 4296 μmol h-1 g-1 under visible light irradiation) coupled with high stability and recyclability, with sustained hydrogen evolution for 50 h.

Photocatalytic conversion of CO2 into fuels is an important challenge for clean energy research and has attracted considerable interest. Here we show that tethering molecular catalysts - a rhenium complex, [Re(bpy)(CO)3Cl] - together in the form of a crystalline covalent organic framework (COF) affords a heterogeneous photocatalyst with a strong visible light absorption, a high CO2 binding affinity, and ultimately an improved catalytic performance over its homogeneous Re counterpart. The COF incorporates bipyridine sites, allowing for ligation of the Re complex, into a fully π-conjugated backbone that is chemically robust and promotes light-harvesting. A maximum rate of 1040 μmol g-1 h-1 for CO production with 81% selectivity was measured. CO production rates were further increased up to 1400 μmol g-1 h-1, with an improved selectivity of 86%, when a photosensitizer was added. Addition of platinum resulted in production of syngas, hence, the co-formation of H2 and CO, the chemical composition of which could be adjusted by varying the ratio of COF to platinum. An amorphous analog of the COF showed significantly lower CO production rates, suggesting that crystallinity of the COF is beneficial to its photocatalytic performance in CO2 reduction.

Membranes with fast and selective ion transport are widely used for water purification and devices for energy conversion and storage including fuel cells, redox flow batteries and electrochemical reactors. However, it remains challenging to design cost-effective, easily processed ion-conductive membranes with well-defined pore architectures. Here, we report a new approach to designing membranes with narrow molecular-sized channels and hydrophilic functionality that enable fast transport of salt ions and high size-exclusion selectivity towards small organic molecules. These membranes, based on polymers of intrinsic microporosity containing Troger’s base or amidoxime groups, demonstrate that exquisite control over subnanometre pore structure, the introduction of hydrophilic functional groups and thickness control all play important roles in achieving fast ion transport combined with high molecular selectivity. These membranes enable aqueous organic flow batteries with high energy efficiency and high capacity retention, suggesting their utility for a variety of energy-related devices and water purification processes. Ion-selective membranes are widely used for water purification and electrochemical energy devices but designing their pore architectures is challenging. Membranes with narrow channels and hydrophilic functionality are shown to exhibit salt ions transport and selectivity towards small organic molecules.

Nature uses organic molecules for light harvesting and photosynthesis, but most man-made water splitting catalysts are inorganic semiconductors. Organic photocatalysts, while attractive because of their synthetic tunability, tend to have low quantum efficiencies for water splitting. Here we present a crystalline covalent organic framework (COF) based on a benzo-bis(benzothiophene sulfone) moiety that shows a much higher activity for photochemical hydrogen evolution than its amorphous or semicrystalline counterparts. The COF is stable under long-term visible irradiation and shows steady photochemical hydrogen evolution with a sacrificial electron donor for at least 50 hours. We attribute the high quantum efficiency of fused-sulfone-COF to its crystallinity, its strong visible light absorption, and its wettable, hydrophilic 3.2 nm mesopores. These pores allow the framework to be dye-sensitized, leading to a further 61% enhancement in the hydrogen evolution rate up to 16.3 mmol g −1 h −1 . The COF also retained its photocatalytic activity when cast as a thin film onto a support.

The physical properties of 3-D porous solids are defined by their molecular geometry. Hence, precise control of pore size, pore shape, and pore connectivity are needed to tailor them for specific applications. However, for porous molecular crystals, the modification of pore size by adding pore-blocking groups can also affect crystal packing in an unpredictable way. This precludes strategies adopted for isoreticular metal–organic frameworks, where addition of a small group, such as a methyl group, does not affect the basic framework topology. Here, we narrow the pore size of a cage molecule, CC3, in a systematic way by introducing methyl groups into the cage windows. Computational crystal structure prediction was used to anticipate the packing preferences of two homochiral methylated cages, CC14-R and CC15-R, and to assess the structure–energy landscape of a CC15-R/CC3-S cocrystal, designed such that both component cages could be directed to pack with a 3-D, interconnected pore structure. The experimental gas sorption properties of these three cage systems agree well with physical properties predicted by computational energy–structure–function maps., The pore size in a molecular crystal, CC3α, is narrowed by introducing methyl groups without disrupting the crystal packing, in line with energy−structure−function maps for these porous crystals.

[Image: see text] Porous organic cages have emerged over the last 10 years as a subclass of functional microporous materials. However, among all of the organic cages reported, large multicomponent organic cages with 20 components or more are still rare. Here, we present an [8 + 12] porous organic imine cage, CC20, which has an apparent surface area up to 1752 m(2) g(–1), depending on the crystallization and activation conditions. The cage is solvatomorphic and displays distinct geometrical cage structures, caused by crystal-packing effects, in its crystal structures. This indicates that larger cages can display a certain range of shape flexibility in the solid state, while remaining shape persistent and porous.

Quantum sieves for hydrogen isotopes One method for improving the efficiency of separation of hydrogen from deuterium (D) is to exploit kinetic quantum sieving with nanoporous solids. This method requires ultrafine pore apertures (around 3 angstroms), which usually leads to low pore volumes and low D 2 adsorption capacities. Liu et al. used organic synthesis to tune the pore size of the internal cavities of organic cage molecules. A hybrid cocrystal contained both a small-pore cage that imparted high selectivity and a larger-pore cage that enabled high D 2 uptake. Science , this issue p. 613

By synthesizing derivatives of a trans-1,2-diaminocyclohexane precursor, three new functionalized porous organic cages were prepared with different chemical functionalities on the cage periphery. The introduction of twelve methyl groups (CC16) resulted in frustration of the cage packing mode, which more than doubled the surface area compared to the parent cage, CC3. The analogous installation of twelve hydroxyl groups provided an imine cage (CC17) that combines permanent porosity with the potential for post-synthetic modification of the cage exterior. Finally, the incorporation of bulky dihydroethanoanthracene groups was found to direct self-assembly towards the formation of a larger [8+12] cage, rather than the expected [4+6], cage molecule (CC18). However, CC18 was found to be non-porous, most likely due to cage collapse upon desolvation.

Soluble additives are widely used to control crystallization, leading to a definition of properties including size, morphology, polymorph, and composition. However, because of the number of potential variables in these experiments, it is typically extremely difficult to identify reaction conditions—as defined by solution compositions, temperatures, and combinations of additives—that give the desired product. This article introduces a high-throughput methodology which addresses this challenge and enables the streamlined preparation and characterization of crystalline materials. Using calcium carbonate precipitated in the presence of selected amino acids as a model system, we use well plates as microvolume crystallizers, and an accurate liquid-handling pipetting workstation for sample preparation. Following changes in the solution turbidity using a plate reader delivers information about the reaction kinetics, while semiautomated scanning electron microscopy, powder X-ray diffraction, and Raman microscopy provide structural information about the library of crystalline products. Of particular interest for the CaCO3 system is the development of fluorescence-based protocols which rapidly evaluate the amounts of the additives occluded within the crystals. Together, these methods provide a strategy for efficiently screening a broad reaction space, where this can both accelerate the ability to generate crystalline materials with target properties and develop our understanding of additive-directed crystallization.

The energy-efficient separation of alkylaromatic compounds is a major industrial sustainability challenge. The use of selectively porous extended frameworks, such as zeolites or metal–organic frameworks, is one solution to this problem. Here, we studied a flexible molecular material, perethylated pillar[n]arene crystals (n = 5, 6), which can be used to separate C8 alkylaromatic compounds. Pillar[6]arene is shown to separate para-xylene from its structural isomers, meta-xylene and ortho-xylene, with 90% specificity in the solid state. Selectivity is an intrinsic property of the pillar[6]arene host, with the flexible pillar[6]arene cavities adapting during adsorption thus enabling preferential adsorption of para-xylene in the solid state. The flexibility of pillar[6]arene as a solid sorbent is rationalized using molecular conformer searches and crystal structure prediction (CSP) combined with comprehensive characterization by X-ray diffraction and 13C solid state NMR spectroscopy. The CSP study, which takes into account the structural variability of pillar[6]arene, breaks new ground in its own right and showcases the feasibility of applying CSP methods to understand and ultimately to predict the behaviour of soft, adaptive molecular crystals.

Stable guest-free porous molecular crystals are uncommon. By contrast, organic molecular crystals with guest-occupied cavities are frequently observed, but these cavities tend to be unstable and collapse on removal of the guests-this feature has been referred to as 'virtual porosity'. Here, we show how we have trapped the virtual porosity in an unstable low-density organic molecular crystal by introducing a second molecule that matches the size and shape of the unstable voids. We call this strategy 'retro-engineering' because it parallels organic retrosynthetic analysis, and it allows the metastable two-dimensional hexagonal pore structure in an organic solvate to be trapped in a binary cocrystal. Unlike the crystal with virtual porosity, the cocrystal material remains single crystalline and porous after removal of guests by heating.

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks. The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less predictable than framework crystallization, and there are fewer examples of ‘reticular synthesis’, where multiple building blocks can be assembled according to a common assembly motif. Here, we apply a chiral recognition strategy to a new family of tubular covalent cages, TCC1–TCC3, to create both 1-D porous nanotubes and 3-D, diamondoid pillared porous networks in a targeted way. The diamondoid networks are analogous to metal-organic frameworks prepared from tetrahedral metal nodes and linear, difunctional organic linkers. The crystal structures can be rationalized by computational lattice energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the ‘node and strut’ principles of reticular synthesis to molecular crystals.

Small structural changes in organic molecules can have a large influence on solid-state crystal packing, and this often thwarts attempts to produce isostructural series of crystalline solids. For metal–organic frameworks and covalent organic frameworks, this has been addressed by using strong, directional intermolecular bonding to create families of isoreticular solids. Here, we show that an organic directing solvent, 1,4-dioxane, has a dominant effect on the lattice energy for a series of organic cage molecules. Inclusion of dioxane directs the crystal packing for these cages away from their lowest-energy polymorphs to form isostructural, 3-dimensional diamondoid pore channels. This is a unique function of the size, chemical function, and geometry of 1,4-dioxane, and hence, a noncovalent auxiliary interaction assumes the role of directional coordination bonding or covalent bonding in extended crystalline frameworks. For a new cage, CC13, a dual, interpenetrating pore structure is formed that doubles the gas uptake and the surface area in the resulting dioxane-directed crystals.

Dynamic nuclear polarization (DNP) solid-state NMR was used to obtain natural abundance (13)C and (15)N CP MAS NMR spectra of microporous organic polymers with excellent signal-to-noise ratio, allowing for unprecedented details in the molecular structure to be determined for these complex polymer networks. Sensitivity enhancements larger than 10 were obtained with bis-nitroxide radical at 14.1 T and low temperature (∼105 K). This DNP MAS NMR approach allows efficient, high-throughput characterization of libraries of porous polymers prepared by combinatorial chemistry methods.

Two [4 + 4] imine cages were synthesized with a unique macrocyclic tetrapod shape. The 3-dimensional structures of both molecules were predicted a priori by using conformer searching routines, illustrating a computational strategy with the potential to target new organic molecules with shape-persistent, intrinsic pores. These methods, in combination with crystal structure prediction, form part of a broader strategy for the computationally led synthesis of functional organic solids.

Molecular crystals cannot be designed in the same manner as macroscopic objects, because they do not assemble according to simple, intuitive rules. Their structures result from the balance of many weak interactions, rather than from the strong and predictable bonding patterns found in metal–organic frameworks and covalent organic frameworks. Hence, design strategies that assume a topology or other structural blueprint will often fail. Here we combine computational crystal structure prediction and property prediction to build energy–structure–function maps that describe the possible structures and properties that are available to a candidate molecule. Using these maps, we identify a highly porous solid, which has the lowest density reported for a molecular crystal so far. Both the structure of the crystal and its physical properties, such as methane storage capacity and guest-molecule selectivity, are predicted using the molecular structure as the only input. More generally, energy–structure–function maps could be used to guide the experimental discovery of materials with any target function that can be calculated from predicted crystal structures, such as electronic structure or mechanical properties.

© 2016 The Royal Society of Chemistry.The practical adsorption properties of molecular porous solids can be dominated by dynamic flexibility but these effects are still poorly understood. Here, we combine molecular simulations and experiments to rationalize the adsorption behavior of a flexible porous organic cage.

Another brick in the wall: Porous ternary cocrystals were prepared by chiral recognition between organic cage modules. One module, CC1, is ordered on 50 % of the lattice positions with respect to two other modules, CC3 and CC4, that are disordered across the other 50 % of sites (see picture). There is a linear relationship between relative module composition and the cocrystal lattice parameters.

The carboxylate ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy)-based on the strongly fluorescent long-lifetime pyrene core-affords a permanently microporous fluorescent metal-organic framework, [In(2)(OH)(2)(TBAPy)].(guests) (1), displaying 54% total accessible volume and excellent thermal stability. Fluorescence studies reveal that both 1 and TBAPy display strong emission bands at 471 and 529 nm, respectively, upon excitation at 390 nm, with framework coordination of the TBAPy ligands significantly increasing the emission lifetime from 0.089 to 0.110 ms. Upon desolvation, the emission band for the framework is shifted to lower energy: however, upon re-exposure to DMF the as-made material is regenerated with reversible fluorescence behavior. Together with the lifetime, the emission intensity is strongly enhanced by spatial separation of the optically active ligand molecules within the MOF structure and is found to be dependent on the amount and chemical nature of the guest species in the pores. The quantum yield of the material is found to be 6.7% and, coupled with the fluorescence lifetime on the millisecond time scale, begins to approach the values observed for Eu(III)-cryptate-derived commercial sensors.

Solid oxide fuel cells (SOFCs) are a major candidate technology for clean energy conversion because of their high efficiency and fuel flexibility.1 The development of intermediate-temperature (500–750 °C) SOFCs requires electrolytes with high oxide ion conductivity (exceeding 10−2 S cm−1 assuming an electrolyte thickness of 15 μm1). This conductivity, in turn, necessitates enhanced understanding of the mechanisms of oxide ion charge carrier creation and mobility at an atomic level. The charge carriers are most commonly oxygen vacancies in fluorites2, 3 and perovskites.3, 4 There are fewer examples of interstitial-oxygen-based conductors such as the apatites5, 6 and La2Mo2O9-based materials,7–9 so information on how these excess anion defects are accommodated and the factors controlling their mobility is important.

Porous materials are important in a wide range of applications including molecular separations and catalysis. We demonstrate that covalently bonded organic cages can assemble into crystalline microporous materials. The porosity is prefabricated and intrinsic to the molecular cage structure, as opposed to being formed by non-covalent self-assembly of non-porous sub-units. The three-dimensional connectivity between the cage windows is controlled by varying the chemical functionality such that either non-porous or permanently porous assemblies can be produced. Surface areas and gas uptakes for the latter exceed comparable molecular solids. One of the cages can be converted by recrystallization to produce either porous or non-porous polymorphs with apparent Brunauer-Emmett-Teller surface areas of 550 and 23 m2 g(-1), respectively. These results suggest design principles for responsive porous organic solids and for the modular construction of extended materials from prefabricated molecular pores.

The development of environmentally benign and scalable synthetic routes to chemically stable covalent organic frameworks (COFs) is key to their real world application in areas such as gas storage and proton conduction. Banerjee et al. [IUCrJ (2016), 3, 402–407] have exploited the high chemical stability of the keto-enamine linkage to develop a ‘green’ water-mediated procedure, presenting a scalable route to chemically robust COFs.

To impact carbon emissions, new materials for carbon capture must be inexpensive, robust, and able to adsorb CO2 specifically from a mixture of other gases. In particular, materials must be tolerant to the water vapor and to the acidic impurities that are present in gas streams produced by using fossil fuels to generate electricity. We show that a porous organic polymer has excellent CO2 capacity and high CO2 selectivity under conditions relevant to precombustion CO2 capture. Unlike polar adsorbents, such as zeolite 13x and the metal-organic framework, HKUST-1, the CO2 adsorption capacity for the hydrophobic polymer is hardly affected by the adsorption of water vapor. The polymer is even stable to boiling in concentrated acid for extended periods, a property that is matched by few microporous adsorbents. The polymer adsorbs CO2 in a different way from rigid materials by physical swelling, much as a sponge adsorbs water. This gives rise to a higher CO2 capacities and much better CO2 selectivity than for other water-tolerant, nonswellable frameworks, such as activated carbon and ZIF-8. The polymer has superior function as a selective gas adsorbent, even though its constituent monomers are very simple organic feedstocks, as would be required for materials preparation on the large industrial scales required for carbon capture.

Imine cage molecules can be reduced to amines to improve their chemical stability, but this introduces molecular flexibility. Hence, amine cages tend not to exhibit permanent solid-state porosity. We report a synthetic strategy to achieve shape persistence in amine cages by tying the cage vertices with carbonyls such as formaldehyde. Shape persistence is predicted by conformer stability calculations, providing a design basis for the strategy. The tied cages show enhanced porosity and unprecedented chemical stability toward acidic and basic conditions (pH 1.7–12.3), where many other porous crystalline solids would fail.

Graphitic carbon nitride has been predicted to be structurally analogous to carbon-only graphite, yet with an inherent bandgap. We have grown, for the first time, macroscopically large crystalline thin films of triazine-based, graphitic carbon nitride (TGCN) using an ionothermal, interfacial reaction starting with the abundant monomer dicyandiamide. The films consist of stacked, two-dimensional (2D) crystals between a few and several hundreds of atomic layers in thickness. Scanning force and transmission electron microscopy show long-range, in-plane order, while optical spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations corroborate a direct bandgap between 1.6 and 2.0 eV. Thus TGCN is of interest for electronic devices, such as field-effect transistors and light-emitting diodes.

The separation of molecules with similar size and shape is an important technological challenge. For example, rare gases can pose either an economic opportunity or an environmental hazard and there is a need to separate these spherical molecules selectively at low concentrations in air. Likewise, chiral molecules are important building blocks for pharmaceuticals, but chiral enantiomers, by definition, have identical size and shape, and their separation can be challenging. Here we show that a porous organic cage molecule has unprecedented performance in the solid state for the separation of rare gases, such as ​krypton and ​xenon. The selectivity arises from a precise size match between the rare gas and the organic cage cavity, as predicted by molecular simulations. Breakthrough experiments demonstrate real practical potential for the separation of ​krypton, ​xenon and ​radon from air at concentrations of only a few parts per million. We also demonstrate selective binding of chiral organic molecules such as ​1-phenylethanol, suggesting applications in enantioselective separation.

Some organic cage molecules have structures with protected, internal pore volume that cannot be in-filled, irrespective of the solid-state packing mode: that is, they are intrinsically porous. Amorphous packings can give higher pore volumes than crystalline packings for these materials, but the precise nature of this additional porosity is hard to understand for disordered solids that cannot be characterized by X-ray diffraction. We describe here a computational methodology for generating structural models of amorphous porous organic cages that are consistent with experimental data. Molecular dynamics simulations rationalize the observed gas selectivity in these amorphous solids and lead to insights regarding self-diffusivities, gas diffusion trajectories, and gas hopping mechanisms. These methods might be suitable for the de novo design of new amorphous porous solids for specific applications, where "rigid host" approximations are not applicable.

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich. This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively. Poly(triazine imide)—a 2D layered network—can be obtained as an intercalation compound with halides from the ionothermal condensation of dicyandiamide in a eutectic salt melt. The gallery height of the intercalated material can be tuned via the composition of the eutectic melt and by post-synthetic modification. Here, we report the synthesis of poly(triazine imide) with intercalated bromide ions (PTI/Br) from a lithium bromide and potassium bromide salt melt. PTI/Br has a hexagonal unit-cell (P63cm (no. 185); a = 8.500390(68) Å, c = 7.04483(17) Å) that contains two layers of imide-bridged triazine (C3N3) units stacked in an AB-fashion as corroborated by solid-state NMR, FTIR spectroscopy and high-resolution TEM. By comparison with a recently reported material PTI/Li+Cl−, prepared from a LiCl/KCl eutectic, the layer-stacking distance in the analogous bromide material was expanded from 3.38 Å to 3.52 Å – an exceptionally large spacing for an aromatic, discotic system (cf. graphite 3.35 Å). Subsequent treatment of PTI/Br with concentrated ammonium fluoride yields poly(triazine imide) with intercalated fluoride ions (PTI/F) (P63/m (no. 176); a = 8.4212(4) Å, c = 6.6381(5) Å) as a statistical phase mix with PTI/Br. Fluoride intercalation leads to a contraction of the gallery height to 3.32 Å, demonstrating that the gallery height is synthetically tuneable in these materials.

The energy-efficient separation of chemical feedstocks is a major sustainability challenge. Porous extended frameworks such as zeolites or metal-organic frameworks are one potential solution to this problem. Here, we show that organic molecules, rather than frameworks, can separate other organic molecules by size and shape. A molecular organic cage is shown to separate a common aromatic feedstock (mesitylene) from its structural isomer (4-ethyltoluene) with an unprecedented perfect specificity for the latter. This specificity stems from the structure of the intrinsically porous cage molecule, which is itself synthesized from a derivative of mesitylene. In other words, crystalline organic molecules are used to separate other organic molecules. The specificity is defined by the cage structure alone, so this solid-state 'shape sorting' is, uniquely, mirrored for cage molecules in solution. The behaviour can be understood from a combination of atomistic simulations for individual cage molecules and solid-state molecular dynamics simulations.

Perovskite oxides with Bi(3+) on the A site are of interest as candidate replacements for lead-based piezoelectric ceramics. Current understanding of the chemical factors permitting the synthesis of ambient-pressure-stable perovskite oxides with Bi(3+) on the A site is limited to information derived from average structures. The local structure of the lead-free ferroelectric perovskite Bi(Ti(3/8)Fe(2/8)Mg(3/8))O(3) is studied by reverse Monte Carlo (RMC) modeling of neutron scattering data. The resultant model is consistent with the structure derived from diffraction but reveals key extra structural features due to correlated local displacements that are inaccessible from the average unit cell. The resulting structural picture emphasizes the need to combine symmetry-averaged long-range and local analysis of the structures of compositionally complex, substitutionally disordered functional materials. Local correlation of the off-axis displacements of the A site cation produces monoclinic domains consistent with the existence of displacement directions other than R (111(p)) or T (100(p)). The Bi displacements are correlated ferroelectrically both in the polar direction and orthogonal to it, providing evidence of the presence of monoclinic domains. The octahedral cation environments reveal distinct differences in the coordination geometry of the different B site metal ions. The local nature of these deviations and correlations makes them inaccessible to long-range averaged techniques. The resulting local structure information provides a new understanding of the stability of pure Bi(3+) A site perovskite oxides.

We present here a simple method for the bottom-up fabrication of microporous organic particles with surface areas in the range 500-1000 m(2) g(-1). The method involves chiral recognition between prefabricated, intrinsically porous organic cage molecules that precipitate spontaneously upon mixing in solution. Fine control over particle size from 50 nm to 1 μm can be achieved by varying the mixing temperature or the rate of mixing. No surfactants or templates are required, and the resulting organic dispersions are stable for months. In this method, the covalent synthesis of the cage modules can be separated from their solution processing into particles because the modules can be dissolved in common solvents. This allows a "mix and match" approach to porous organic particles. The marked solubility change that occurs upon mixing cages with opposite chirality is rationalized by density functional theory calculations that suggest favorable intermolecular interactions for heterochiral cage pairings. The important contribution of molecular disorder to porosity and surface area is highlighted. In one case, a purposefully amorphized sample has more than twice the surface area of its crystalline analogue.

Control over pore size, shape, and connectivity in synthetic porous materials is important in applications such as separation, storage, and catalysis. Crystalline organic cage molecules can exhibit permanent porosity, but there are few synthetic methods to control the crystal packing and hence the pore connectivity. Typically, porosity is either 'intrinsic' (within the molecules) or 'extrinsic' (between the molecules)--but not both. We report a supramolecular approach to the assembly of porous organic cages which involves bulky directing groups that frustrate the crystal packing. This generates, in a synthetically designed fashion, additional 'extrinsic' porosity between the intrinsically porous cage units. One of the molecular crystals exhibits an apparent Brunauer-Emmett-Teller surface area of 854 m(2) g(-1), which is higher than that of unfunctionalized cages of the same dimensions. Moreover, connectivity between pores, and hence guest uptakes, can be modulated by the introduction of halogen bonding motifs in the cage modules. This suggests a broader approach to the supramolecular engineering of porosity in molecular organic crystals.

The coordination of adenine to Ni(2+) forms a dimer unit which can be linked by 3,5-pyrazoledicarboxylic acid into chains which assemble under hydrothermal conditions via hydrogen bonding into a robust porous network. The material displays selectivity for CO(2) over CH(4) and an isosteric heat which increases with guest loading.

Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for 'one-pot' chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules.

Swelling Pores Porosity is a key parameter when selecting materials for catalysts, chemical separations, gas storage, host-guest interactions, and related chemical processes. In most cases the porosity of a material is fixed. Rabone et al. (p. 1053 ; see the Perspective by Wright ) have described a molecular material in which the size of the pores changed during the sorption process. The porosity increased because a dipeptide linker between metal centers reoriented during uptake of some gases, thus improving the capacity of the material to adsorb.

The principles of social and biological evolution have been combined in a Cultural Differential Evolution hybrid global optimization technique and applied to crystal structure solution.

The crystal structures of triethyl-1,3,5-triazine-2,4,6-tricarboxylate (I), triethyl-1,3,5-benzenetricarboxylate (II) and tris-2-hydroxyethyl isocyanurate (III) have been determined from conventional laboratory X-ray powder diffraction data using the differential evolution structure solution technique. The determination of these structures presented an unexpectedly wide variation in levels of difficulty, with only the determination of (III) being without complication. In the case of (I) structure solution resulted in a Rietveld refinement profile that was not ideal, but was subsequently rationalized by single-crystal diffraction as resulting from disorder. Refinement of structure (II) showed significant variation in side-chain conformation from the initial powder structure solution. Further investigation showed that the structure solution optimization had indeed been successful, and that preferred orientation had a dramatic effect on the structure-solution R-factor search surface. Despite the presence of identical side chains in (I) and (II), only the triazine-based system retains threefold molecular symmetry in the crystal structure. The lack of use of the heterocyclic N atom as a hydrogen-bond acceptor in this structure results in the formation of a similar non-centrosymmetric network to the benzene-based structure, but with overall three-dimensional centrosymmetry. The hydrogen-bonded layer structure of (III) is similar to that of other isocyanurate-based structures of this type.

Intensive research into microporous materials has been driven by potential applications in areas such as catalysis, gas separation, storage, and sensing. Recently, a new class of purely organic molecular cage materials has emerged, which can exhibit significant porosity arising from the internal molecular cavity as well as extrinsic porosity from packing in the crystal structure [1]. Unlike extended frameworks, porous molecular materials lack strongly directional interactions to drive their assembly, complicating the crystal engineering possible for isoreticular metal-organic frameworks [2], for example. Our work has focused on covalent imine-linked cages, which exhibit diverse crystal chemistry. The connectivity of the pore network is derived from the cage packing: Therefore, the crystal structure directly affects the observed porosity. The imine cages synthesised so far lack strongly hydrogen bonding groups. Thus, the solid state supramolecular assembly of cage molecules is governed by the aggregate of weak interactions, such as van der Waals forces. By identifying robust `tectons', that is, regularly occurring supramolecular motifs, progress toward designing the crystal structure and therefore controlling the physical properties of organic cage materials becomes possible. Here, we report exploiting robust supramolecular motifs, comprising either cage modules or host and guest molecules to gain control over the porosity of the bulk material. We demonstrate how formation of a desired void network topology can be driven by hosting a specific guest in preferred sites which maximise weak host-guest interactions [3]. Subsequent guest removal can produce stable polymorphs, one of which exhibited double the Brunauer-Emmett-Teller surface area with respect to the originally observed polymorph. We also examine how the interaction between gas phase guests and cage host is important in the application of porous organic cages in rare gas separation.