Homochiral metal–organic framework used as a stationary phase for high‐performance liquid chromatography

Metal–organic frameworks are promising porous materials. Chiral metal–organic frameworks have attracted considerable attention in controlling enantioselectivity. In this study, a homochiral metal–organic framework [Co₂(D‐cam)₂(TMDPy)] (D‐cam = d ‐camphorates, TMDPy = 4,4′‐trimethylenedipyridine) with a non‐interpenetrating primitive cubic net has been used as a chiral stationary phase in high‐performance liquid chromatography. It has allowed the successful separation of six positional isomers and six chiral compounds. The good selectivity and baseline separation, or at least 60% valley separation, confirmed its excellent molecular recognition characteristics. The relative standard deviations for the retention time of run‐to‐run and column‐to‐column were less than 1.8 and 3.1%, respectively. These results demonstrate that [Co₂(D‐cam)₂(TMDPy)] may represent a promising chiral stationary phase for use in high‐performance liquid chromatography.     

Water‐Soluble Three‐Dimensional Polymers: Non‐Covalent and Covalent Synthesis and Functions†

Water‐soluble three‐dimensional (3D) polymers are structurally ideal for the construction of ordered porous materials for in‐situ and tunable loading and release of guests. For many years, studies on ordered porous materials have been confined to crystalline solids. Since 2014, self‐assembly has been developed as a robust strategy for the preparation of water‐soluble 3D polymers that possess defined and intrinsic porosity. Through the encapsulation of cucurbit[8]uril for aromatic dimers, ordered diamondoid supramolecular organic frameworks can be assembled from tetrahedral monomers. With [Ru(bipy)₃]²⁺‐derived octahedral complexes as precursors, cubic supramolecular metal‐organic frameworks have been assembled. One supramolecular organic framework has also been utilized to prepare the first homogeneous covalent organic framework through the [2+2] alkene cycloaddition, whereas the quantitative formation of the hydrazone bonds can be utilized to synthesize flexible porous organic frameworks. The new water‐soluble ordered and flexible polymeric frameworks are able to include drugs and biomacromolecules to accomplish in situ loading and intracellular delivery and to enrich photosensitizers and catalysts to enhance discrete visible light‐induced reactions. This review highlights the advances.     

Intercalation of Varied Sulfonates into a Layered MOC: Confinement‐Caused Tunable Luminescence and Novel Properties

The pores/channels of porous 3D metal–organic frameworks (MOFs) have been widely applied to incorporate gas, solvent, or organic molecules. On the contrary, the utilization of the interlamellar void of layered metal–organic complexes (MOCs) remains underappreciated, although it is more flexible and available to accommodate molecules with different sizes. In this work, diverse sulfonates have been intercalated purposely into an identical layered MOC, which constructed various novel intercalation compounds possessing fluorescent, white‐light emitting, photochromic, homochiral, or nonlinear optical (NLO) properties. With the help of single‐crystal X‐ray diffraction, their structures and the mutual interactions between the MOC host and the sulfonate guests were characterized. The properties of the guest molecules were tuned and meanwhile some new performances were generated after confining them into the interlayer region. Such a hybrid approach provides an efficient strategy to design and prepare multifunctional materials.     

Hydrogen‐Bonded Organic Aromatic Frameworks for Ultralong Phosphorescence by Intralayer π–π Interactions

Ultralong organic phosphorescence (UOP) based on metal‐free porous materials is rarely reported owing to rapid nonradiative transition under ambient conditions. In this study, hydrogen‐bonded organic aromatic frameworks (HOAFs) with different pore sizes were constructed through strong intralayer π–π interactions to enable ultralong phosphorescence in metal‐free porous materials under ambient conditions for the first time. Impressively, yellow UOP with a lifetime of 79.8 ms observed for PhTCz‐1 lasted for several seconds upon ceasing the excitation. For PhTCz‐2 and PhTCz‐3, on account of oxygen‐dependent phosphorescence quenching, UOP could only be visualized in N₂, thus demonstrating the potential of phosphorescent porous materials for oxygen sensing. This result not only outlines a principle for the design of new HOFs with high thermal stability, but also expands the scope of metal‐free luminescent materials with the property of UOP.     

Highly Efficient Enrichment of Volatile Iodine by Charged Porous Aromatic Frameworks with Three Sorption Sites

The targeted synthesis of a series of novel charged porous aromatic frameworks (PAFs) is reported. The compounds PAF‐23, PAF‐24, and PAF‐25 are built up by a tetrahedral building unit, lithium tetrakis(4‐iodophenyl)borate (LTIPB), and different alkyne monomers as linkers by a Sonogashira–Hagihara coupling reaction. They possess excellent adsorption properties to organic molecules owing to their “breathing” dynamic frameworks. As these PAF materials assemble three effective sorption sites, namely the ion bond, phenyl ring, and triple bond together, they exhibit high affinity and capacity for iodine molecules. To the best of our knowledge, these PAF materials give the highest adsorption values among all porous materials (zeolites, metal–organic frameworks, and porous organic frameworks) reported to date.     

Control of porosity geometry in amino acid derived nanoporous materials

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.     

Exceptional CO2 Adsorbing Materials under Different Conditions

In this article we discuss those materials that have recorded the highest adsorption capacities for the greenhouse gas CO₂ under ambient conditions as well as at different temperatures and pressures. For convenience, the materials have been categorized under four categories, viz., porous carbon, metal–organic, zeolite and mesoporous silica, and porous organic frameworks. It has been found that the gas adsorption property significantly relies on several factors such as high surface area and pore volume and the presence of N‐, O‐ and S‐containing moieties. The presence of a microporous structure and strong interaction between the CO₂ molecules with the framework through H‐bonding or dipole–quadrupole interactions facilitates adsorption of the gas.     

Rational Design of MOF/COF Hybrid Materials for Photocatalytic H2 Evolution in the Presence of Sacrificial Electron Donors

Crystalline and porous covalent organic frameworks (COFs) and metal‐organic frameworks (MOFs) materials have attracted enormous attention in the field of photocatalytic H₂ evolution due to their long‐range order structures, large surface areas, outstanding visible light absorbance, and tunable band gaps. In this work, we successfully integrated two‐dimensional (2D) COF with stable MOF. By covalently anchoring NH₂‐UiO‐66 onto the surface of TpPa‐1‐COF, a new type of MOF/COF hybrid materials with high surface area, porous framework, and high crystallinity was synthesized. The resulting hierarchical porous hybrid materials show efficient photocatalytic H₂ evolution under visible light irradiation. Especially, NH₂‐UiO‐66/TpPa‐1‐COF (4:6) exhibits the maximum photocatalytic H₂ evolution rate of 23.41 mmol g^?1 h^?1 (with the TOF of 402.36 h^?1), which is approximately 20 times higher than that of the parent TpPa‐1‐COF and the best performance photocatalyst for H₂ evolution among various MOF‐ and COF‐based photocatalysts.     

Supramolecular Porphyrin‐Based Metal–Organic Frameworks with Fullerenes: Crystal Structures and Preferential Intercalation of C70

The syntheses and characterization of two new porphyrin‐based metal–organic frameworks (P‐MOFs), through the complexation of 5,10,15,20‐tetra‐4‐pyridyl‐21 H,23 H‐porphine (H₂TPyP) and copper(II) acetate (CuAcO) in the presence of the fullerenes C₆₀ or C₇₀ are reported. Complex 1 was synthesized in conjunction with C₆₀, and this reaction produced a two‐dimensional (2D) porous structure with the composition CuAcO‐CuTPyP?m‐dichlorobenzene (m‐DCB), in which C₆₀ molecules were not intercalated. Complex 2 was synthesized in the presence of C₇₀, generating a three‐dimensional (3D) porous structure, in which C₇₀ was intercalated, with the composition CuAcO‐CuTPyP?C₇₀?m‐DCB?CHCl₃. The structures of these materials were determined by X‐ray diffraction to identify the supramolecular interactions that lead to 2D and 3D crystal packing motifs. When a combination of C₆₀ and C₇₀ was employed, C₇₀ was found to be preferentially intercalated between the porphyrins.     

Topology‐Templated Synthesis of Crystalline Porous Covalent Organic Frameworks

A strategy is presented for the synthesis of crystalline porous covalent organic frameworks via topology‐templated polymerization. The template is based on imine‐linked frameworks and their (001) facets seed the C=C bond formation reaction to constitute 2D sp² carbon‐conjugated frameworks. This strategy is applicable to templates with different topologies, enables designed synthesis of frameworks that cannot be prepared via direct polymerization, and creates a series of sp² carbon frameworks with tetragonal, hexagonal, and kagome topologies. The sp² carbon frameworks are highly luminescent even in the solid state and exhibit topology‐dependent π transmission and exciton migration; these key fundamental π functions are unique to sp² carbon‐conjugated frameworks and cannot be accessible by imine‐linked frameworks, amorphous analogues, and 1D conjugated polymers. These results demonstrate an unprecedented strategy for structural and functional designs of covalent organic frameworks.     

A Molecular Pillar Approach To Grow Vertical Covalent Organic Framework Nanosheets on Graphene: Hybrid Materials for Energy Storage

Hybrid 2D–2D materials composed of perpendicularly oriented covalent organic frameworks (COFs) and graphene were prepared and tested for energy storage applications. Diboronic acid molecules covalently attached to graphene oxide (GO) were used as nucleation sites for directing vertical growth of COF‐1 nanosheets (v‐COF‐GO). The hybrid material has a forest of COF‐1 nanosheets with a thickness of 3 to 15 nm in edge‐on orientation relative to GO. The reaction performed without molecular pillars resulted in uncontrollable growth of thick COF‐1 platelets parallel to the surface of GO. The v‐COF‐GO was converted into a conductive carbon material preserving the nanostructure of precursor with ultrathin porous carbon nanosheets grafted to graphene in edge‐on orientation. It was demonstrated as a high‐performance electrode material for supercapacitors. The molecular pillar approach can be used for preparation of many other 2D‐2D materials with control of their relative orientation.     

Incorporation of metal‐organic framework amino‐modified MIL‐101 into glycidyl methacrylate monoliths for nano LC separation

Metal‐organic frameworks consisting of amino‐modified MIL‐101(M: Cr, Al, and Fe) crystals have been synthesized and subsequently incorporated to glycidyl methacrylate monoliths to develop novel stationary phases for nano‐liquid chromatography. Two incorporation approaches of these materials in monoliths were explored. The metal‐organic framework materials were firstly attached to the pore surface through reaction of epoxy groups present in the parent glycidyl methacrylate‐based monolith. Alternatively, NH₂‐MIL‐101(M) were admixed in the polymerization mixture. Using short time UV‐initiated polymerization, monolithic beds with homogenously dispersed metal‐organic frameworks were obtained. The chromatographic performance of embedded UV‐initiated composites was demonstrated with separations of polycyclic aromatic hydrocarbons and non‐steroidal anti‐inflammatory drugs as test solutes. In particular, the incorporation of the NH₂‐MIL‐101(Al) into the organic polymer monoliths led to an increase in the retention of all the analytes compared to the parent monolith. The hybrid monolithic columns also exhibited satisfactory run‐to‐run and column‐to‐column reproducibility.     

Selective CO2 Adsorption in a Supramolecular Organic Framework

Considering the rapidly rising CO₂ level, there is a constant need for versatile materials which can selectively adsorb CO₂ at low cost. The quest for efficient sorptive materials is still on since the practical applications of conventional porous materials possess certain limitations. In that context, we designed, synthesized, and characterized two novel supramolecular organic frameworks based on C‐pentylpyrogallol[4]arene (PgC₅) with spacer molecules, such as 4,4′‐bipyridine (bpy). Highly optimized and symmetric intermolecular hydrogen‐bonding interactions between the main building blocks and comparatively weak van der Waals interactions between solvent molecules and PgC₅ leads to the formation of robust extended frameworks, which withstand solvent evacuation from the crystal lattice. The evacuated framework shows excellent affinity for carbon dioxide over nitrogen and adsorbs ca. 3 wt % of CO₂ at ambient temperature and pressure.     

Microporous Metal–Organic Frameworks for Gas Separation

Microporous metal–organic frameworks (MOFs) are comparatively new porous materials. Because the pores within such MOFs can be readily tuned through the interplay of both metal‐containing clusters and organic linkers to induce their size‐selective sieving effects, while the pore surfaces can be straightforwardly functionalized to enforce their different interactions with gas molecules, MOF materials are very promising for gas separation. Furthermore, the high porosities of such materials can enable microporous MOFs with optimized gas separation selectivity and capacity to be targeted. This Focus Review highlights recent significant advances in microporous MOFs for gas separation.     

In Situ Generation and Stabilization of Accessible Cu/Cu2O Heterojunctions inside Organic Frameworks for Highly Efficient Catalysis

Heterostructural metal/metal oxides are the very promising substituents of noble‐metal catalysts; however, generation and further stabilization of accessible metal/metal oxide heterojunctions are very difficult. A strategy to encapsulate and stabilize Cu/Cu₂O nanojunctions in porous organic frameworks in situ is developed by tuning the acrylate contents in copper‐based metal–organic frameworks (Cu‐MOFs) and the pyrolytic conditions. The acrylate groups play important roles on improving the polymerization degree of organic frameworks and generating and stabilizing highly dispersed and accessible Cu/Cu₂O heteronanojunctions. As a result, pyrolysis of the MOF ZJU‐199, consisting of three acrylates per ligand, generates abundant heterostructural Cu/Cu₂O discrete domains inside porous organic matrices at 350 °C, demonstrating excellent catalytic properties in liquid‐phase hydrogenation of furfural into furfuryl alcohol, which are much superior to the non‐noble metal‐based catalysts.     

Synergistically Directed Assembly of Aromatic Stacks Based Metal‐Organic Frameworks by Donor‐Acceptor and Coordination Interactions

A synergistically directed assembly approach to distinctive metal‐organic frameworks utilizing both donor‐acceptor (D‐A) interaction from aromatic systems and coordination interactions is presented. Based on such an approach, the coronene‐tpt (tpt = 2,4,6‐tri(4‐pyridyl)‐1,3,5‐triazine) stacks based coronene‐MOF‐1 — 4 have been successfully fabricated. Their structural discrepancies with coronene‐ absent control products, 1′ — 4′ , illustrate clearly the significance of coronene‐tpt based D‐A interactions in these architectures. All these coronene‐MOFs contain varied coronene‐tpt stacks as organic secondary building blocks (SBUs), which are closely interrelated with the coordination based framework structures. Moreover, porous coronene‐MOF‐1 and ‐2 exhibit high physicochemical stability and significant light hydrocarbons storage and separation performances.     

A Mixed Molecular Building Block Strategy for the Design of Nested Polyhedron Metal–Organic Frameworks

A mixed molecular building block (MBB) strategy for the synthesis of double‐walled cage‐based porous metal–organic frameworks (MOFs) is presented. By means of this method, two isostructural porous MOFs built from unprecedented double‐walled metal–organic octahedron were obtained by introducing two size‐matching C₃‐symmetric molecular building blocks with different rigidities. With their unique framework structures, these MOFs provide, to the best of our knowledge, the first examples of double‐walled octahedron‐based MOFs.     

Beyond Molecules: Mesoporous Supramolecular Frameworks Self‐Assembled from Coordination Cages and Inorganic Anions

Biological function arises by the assembly of individual biomolecular modules into large aggregations or highly complex architectures. A similar strategy is adopted in supramolecular chemistry to assemble complex and highly ordered structures with advanced functions from simple components. Here we report a series of diamond‐like supramolecular frameworks featuring mesoporous cavities, which are assembled from metal‐imidazolate coordination cages and various anions. Small components (metal ions, amines, aldehydes, and anions) are assembled into the hierarchical complex structures through multiple interactions including covalent bonds, dative bonds, and weak C? H???X (X=O, F, and π) hydrogen bonds. The mesoporous cavities are large enough to trap organic dye molecules, coordination cages, and vitamin B₁₂. The study is expected to inspire new types of crystalline supramolecular framework materials based on coordination motifs and inorganic ions.     

Organization and Energy Transfer of Fused Aromatic Hydrocarbon Guests within Anion‐Confining Nanochannel MOFs

The self‐assembly of Zn^II ions with 1,3,5‐tris(isonicotinoyloxyethyl)cyanurate produces new topological (4²?12⁴)₃(4³)₄ 2D metal–organic frameworks (MOFs) with anion‐confining cages. The eclipsed assembly of each 2D MOF by π–π stacking of cyanurate moieties (3.352(5) Å) forms 3D MOFs consisting of nanochannels (10.5 Å). Two of the three anions are confined in each peanut‐type cage, resulting in hydrophobicity of the nanochannels. The hydrophobic nanochannel effectively adsorbs a wide range of fused aromatic hydrocarbons (FAHs) as monomers or dimers, rendering it potentially highly useful as an energy‐transfer material.     

A Hydrophobic Metal–Organic Framework Based on Cubane‐Type [Co4(μ3‐F)3(μ3‐SO4)]3+ Clusters for Gas Storage and Adsorption Selectivity of Benzene over Cyclohexane

Hydrophobic metal‐organic frameworks (MOFs) not only have high water stability, but also exhibit high adsorption capacity towards organic molecules, in particular hydrocarbons. Herein we report a rare metal fluoride organic framework MFOF‐1 with high hydrophobicity, which is constructed from unprecedented fluoride‐ and sulfate‐bridged cubane‐type tetranuclear cobalt clusters. MFOF‐1 consists of three types of polyhedral cages with face‐sharing configurations, and possesses a novel (3,9)‐connected 3D+3D→3D self‐interpenetrating array or the rare pyr topology. MFOF‐1 shows high thermal stability and high stability in water and even acid/base aqueous solutions, and exhibits rather high H₂ and CO₂ storage capacities at ambient pressure. Remarkably, MFOF‐1 shows little adsorption of water but considerably high uptakes of methanol, n‐hexane, cyclohexane, and benzene, and exhibits a certain degree of adsorption selectivity of benzene over cyclohexane.