Hierarchical Self-Assembly of Capsule-Shaped Zirconium Coordination Cages with Quaternary Structure.

Biological macromolecules exhibit emergent functions through hierarchical self-assembly, a concept that is extended to design artificial supramolecular assemblies. Here, the first example of breaking the common parallel arrangement of capsule-shaped zirconium coordination cages is reported by constructing the hierarchical porous framework ZrR-1. ZrR-1 adopts a quaternary structure resembling protein and contains 12-connected chloride clusters, representing the highest connectivity for zirconium-based cages reported thus far. Compared to the parallel framework ZrR-2, ZrR-1 demonstrated enhanced stability in acidic aqueous solutions and a tenfold increase in BET surface area (879 m2  g-1 ). ZrR-1 also exhibits excellent proton conductivity, reaching 1.31 × 10-2 S·cm-1 at 353 K and 98% relative humidity, with a low activation energy of 0.143 eV. This finding provides insights into controlling the hierarchical self-assembly of metal-organic cages to discover superstructures with emergent properties.

Effect of Functional Groups on Low-Concentration Carbon Dioxide Capture in UiO-66-Type Metal-Organic Frameworks.

The selective capture of low-concentration CO2 from air or confined spaces remains a great challenge. In this study, various functional groups were introduced into UiO-66 to generate functionalized derivatives (UiO-66-R, R = NO2, NH2, OH, and CH3), aiming at significantly enhancing CO2 adsorption and separation efficiency. More significantly, UiO-66-NO2 and UiO-66-NH2 with high polarity exhibit exceptional CO2 affinity and optimal separation characteristics in mixed CO2/O2/N2 (1:21:78). In addition, the impressive stability of UiO-66-NO2 and UiO-66-NH2 endows them with excellent recycling stability. The effective adsorption and separation performances demonstrated by these two functional materials suggest their potential as promising physical adsorbents for capturing low-concentration CO2.

Chiral proline-substituted porous organic cages in asymmetric organocatalysis.

The efficient preparation of chiral porous organic cages (POCs) with specific functions is challenging, and their application in asymmetric catalysis has not previously been explored. In this work, we have achieved the construction of chiral POCs based on a supramolecular tetraformyl-resorcin[4]arene scaffold with different chiral proline-modified diamine ligands and utilizing dynamic imine chemistry. The incorporation of V-shaped or linear chiral diamines affords the [4 + 8] square prism and [6 + 12] octahedral POCs respectively. The appended chiral proline moieties in such POCs make them highly active supramolecular nanoreactors for asymmetric aldol reactions, delivering up to 92% ee. The spatial distribution of chiral catalytic sites in these two types of POCs greatly affects their catalytic activities and enantioselectivities. This work not only lays a foundation for the asymmetric catalytic application of chiral POCs, but also contributes to our understanding of the catalytic function of biomimetic supramolecular systems.

Water-stable hydrazone-linked porous organic cages.

Although porous organic cages (POCs), particularly imine-linked (C[double bond, length as m-dash]N) ones, have advanced significantly over the last few decades, the reversible nature of imine linkages makes them prone to hydrolysis and structural collapse, severely limiting their applications under moist or water conditions. Herein, seven water-stable hydrazone-linked (C[double bond, length as m-dash]N-N) POCs are prepared through a simple coupling of the same supramolecular tetraformylresorcin[4]arene cavitand with different dihydrazide linkers. Their structures are all determined by single-crystal X-ray crystallography, demonstrating rich structural diversity from the [2 + 4] lantern, [3 + 6] triangular prism, and unprecedented [4 + 8] square prism to the extra-large [6 + 12] octahedron. In addition, they respectively exhibit tunable window diameters and cavity volumes ranging from about 5.4 to 11.1 nm and 580 to 6800 Å3. Moreover, their application in the water environment for pollutant removal was explored, indicating that they can effectively eliminate various types of contaminants from water, including radionuclide waste, toxic heavy metal ions, and organic micropollutants. This work demonstrates a convenient method for rationally constructing versatile robust POCs and presents their great application potentialities in water medium.

Efficient ethylene purification by a robust ethane-trapping porous organic cage.

The removal of ethane (C2H6) from its analogous ethylene (C2H4) is of paramount importance in the petrochemical industry, but highly challenging due to their similar physicochemical properties. The use of emerging porous organic cage (POC) materials for C2H6/C2H4 separation is still in its infancy. Here, we report the benchmark example of a truncated octahedral calix[4]resorcinarene-based POC adsorbent (CPOC-301), preferring to adsorb C2H6 than C2H4, and thus can be used as a robust absorbent to directly separate high-purity C2H4 from the C2H6/C2H4 mixture. Molecular modelling studies suggest the exceptional C2H6 selectivity is due to the suitable resorcin[4]arene cavities in CPOC-301, which form more multiple C-H···π hydrogen bonds with C2H6 than with C2H4 guests. This work provides a fresh avenue to utilize POC materials for highly selective separation of industrially important hydrocarbons.

Solvatomorphism Influence of Porous Organic Cage on C2H2/CO2 Separation.

Porous organic molecular (POM) materials can exhibit solvatomorphs via altering their crystallographic packing in the solid state, but investigating real gas mixture separation by porous materials with such a behavior is still very rare. Herein, we report that a lantern-shaped calix[4]resorcinarene-based porous organic cage (POC, namely, CPOC-101) can exhibit eight distinct solid-state solvatomorphs via crystallization in different solvents. This POC solvatomorphism has a significant influence on their gas sorption capacities as well as separation abilities. Specifically, the apparent Brunauer-Emmett-Teller (BET) surface area determined by nitrogen gas sorption at 77 K for CPOC-101α crystallized from toluene/chloroform is up to 406 m2 g-1, which is much higher than the rest of CPOC-101 solvatomorphs with BET values less than 40 m2 g-1. More interestingly, C2H2 and CO2 adsorbed capacities, in addition to the C2H2/CO2 separation ability at room temperature for CPOC-101α, are superior to those of CPOC-101ß crystalized from nitrobenzene, the representative of POC solvatomorphs with low BET surface areas. These results indicate the possibility of adjusting gas sorption and separation properties of POC materials by controlling their solvatomorphs.

Reticular Chemistry in the Construction of Porous Organic Cages.

Reticular chemistry offers the possibility of systematic design of porous materials with different pores by varying the building blocks, while the emerging porous organic cage (POC) system remains generally unexplored. A series of new POCs with dimeric cages with odd-even behaviors, unprecedented trimeric triangular prisms, and the largest recorded hexameric octahedra have been prepared. These POCs are all constructed from the same tetratopic tetraformylresorcin[4]arene cavitand by simply varying the diamine ligands through Schiff-base reactions and are fully characterized by X-ray crystallography, gas sorption measurements, NMR spectroscopy, and mass spectrometry. The odd-even effects in the POC conformation changes of the [2 + 4] dimeric cages have been confirmed by density functional theory calculations, which are the first examples of odd-even effects reported in the cavitand-based cage system. Moreover, the "V" shape phenylenediamine linkers are responsible for the novel [3 + 6] triangular prisms. The window size and environment can be easily functionalized by different groups, providing a promising platform for the construction of multivariate POCs. Use of linear phenylenediamines led to record-breakingly large [6 + 12] truncated octahedral cages, the maximum inner cavity diameters and volumes of which could be readily modulated by increasing the spacer length of the phenylenediamine linkers. This work can lead to an understanding of the self-assembly behaviors of POCs and also sheds light on the rational design of POC materials for practical applications.

Structural and Morphological Conversion between Two Co-Based MOFs for Enhanced Water Oxidation.

The rapid development of suitable and cheap water oxidation catalysts is of great significance in energy conversion and storage. In this context, herein we have synthesized two different types of metal-organic frameworks (MOFs, denoted as BMM-11 and BMM-12) constructed from the same metal salts (cobalt nitrate) and organic linkers (H4BPTC) at the similar solvothermal conditions. Interestingly, we learned that both crystalline materials can be conveniently converted into each other by a single-crystal-to-single-crystal transformation method at their corresponding synthetic conditions. Meanwhile, we applied them directly as electrocatalysts into OER application where the pure BMM-11 and BMM-12 can achieve a stable current density of 10 mA cm-2 with an overpotential of 0.362 and 0.393 V, respectively, during which MOF degradation unexpectedly occurs. After electrolysis, the following microscopic, spectroscopic, as well as electrochemical measurements confirm that these initial MOF precursors are rapidly transformed into the mixed phases of CoOxHy species consisting of CoOOH and Co(OH)2, which are essentially active components for OER performance. Finally, we have also considered other strategies to improve MOF-derived composites in oxygen evolution activity, including bimetallic doping and physical grinding strategy. The approach described here can further be extended to other cobalt-based MOFs-derived electrocatalysts for water splitting.

A Reusable MOF-Supported Single-Site Zinc(II) Catalyst for Efficient Intramolecular Hydroamination of o-Alkynylanilines.

The exploitation of new and active earth-abundant metal catalysts is critical for sustainable chemical production. Herein, we demonstrate the design of highly efficient, robust, and reusable ZnII -bipyridine-based metal-organic framework (MOF) catalysts for the intramolecular hydroamination of o-alkynylanilines to indoles. Under similar conditions homogeneous catalytic systems mainly provide hydrolysate. Our results prove that MOFs support unique internal environments that can affect the direction of chemical reactions. The ZnII -catalyzed hydroamination reaction can be conducted without additional ligands, base, or acid, and is thus a very clean reaction system with regard to its environmental impact.

Interconvertible vanadium-seamed hexameric pyrogallol[4]arene nanocapsules.

Research into stimuli-responsive controlled self-assembly and reversible transformation of molecular architectures has received much attention recently, because it is important to understand and reproduce this natural self-assembly behavior. Here, we report two coordination nanocapsules with variable cavities: a contracted octahedral V24 capsule and an expanded ball-shaped V24 capsule, both of which are constructed from the same number of subcomponents. The assemblies of these two V24 capsules are solvent-controlled, and capable of reversible conversion between contracted and expanded forms via control of the geometries of the metal centers by association and dissociation with axial water molecules. Following such structural interconversions, the magnetic properties are significantly changed. This work not only provides a strategy for the design and preparation of coordination nanocapsules with adaptable cavities, but also a unique example with which to understand the transformation process and their structure-property relationships.

A monomeric bowl-like pyrogallol[4]arene Ti12 coordination complex.

Herein, an unprecedented monomeric bowl-like coordination complex, Ti12PgC3 (PgC3 = C-propylpyrogallol[4]arene), has been successfully synthesized. To the best of our knowledge, Ti12PgC3 not only presents the first pyrogallol[4]arene-based titanium coordination complex, but also the highest nuclearity titanium coordination complex in the metal-calixarene system. In addition, this titanium coordination complex can effectively degrade the methylene blue (MB) dye under sunlight.

Controlled Orthogonal Self-Assembly of Heterometal-Decorated Coordination Cages.

Multiple orthogonal coordinative interactions were utilized to construct heterometal-decorated tetrahedral cages from in situ formed trinuclear ZrIV clusters through the combination with other metal ions such as CuII or PdII . Through effective use of the hard/soft acid/base principle, the orthogonal self-assembly process of Zr-bpydc-CuCl2 (H2 bpydc=2,2-bipyridine-5,5-dicarboxylic acid) can be finely controlled using three strategies: post-synthetic metallization, a stepwise metalloligand approach, or a one-pot reaction.

Cuboctahedron-based indium-organic frameworks for gas sorption and selective cation exchange.

[Me2NH2]3[In3(BTB)4]·2DMF·2DMA·28H2O (InOF-9) is an anionic indium-organic framework based on nanosized cuboctahedrons, which is sustained by tetrahedral [In(COO)4] nodes and 3-connected tricarboxylates. Although InOF-9 is structurally unstable when exposed to air, it exhibits excellent gas sorption capacity through a supercritical carbon dioxide activation process and selectively encapsulates guest methylene blue cations.

Visualizing the Dynamics of Temperature- and Solvent-Responsive Soft Crystals.

We demonstrate that three flexible MOFs termed FJI-H11-R (FJI-H=Hong's group in Fujian Institute of Research on the Structure of Matter, R=Me, Et, (i) Pr) can reversibly respond to temperature and solvents via structural transformations, which can be visualized by in situ single-crystal X-ray snapshot analyses. FJI-H11-R exhibit colossal anisotropic thermal expansion, with a record-high uniaxial positive thermal-expansion coefficient of 653.2×10(-6)  K(-1) observed in FJI-H11-Me. Additionally, large c-axial shrinkage of 32.4 % is also observed during desolvation. The stimuli-responsive mechanism reveals the structural evolutions are related to the rotations and deformations of the organic linkers.

A porous metal-organic framework with ultrahigh acetylene uptake capacity under ambient conditions.

Acetylene, an important petrochemical raw material, is very difficult to store safely under compression because of its highly explosive nature. Here we present a porous metal-organic framework named FJI-H8, with both suitable pore space and rich open metal sites, for efficient storage of acetylene under ambient conditions. Compared with existing reports, FJI-H8 shows a record-high gravimetric acetylene uptake of 224 cm(3) (STP) g(-1) and the second-highest volumetric uptake of 196 cm(3) (STP) cm(-3) at 295 K and 1 atm. Increasing the storage temperature to 308 K has only a small effect on its acetylene storage capacity (∼200 cm(3) (STP) g(-1)). Furthermore, FJI-H8 exhibits an excellent repeatability with only 3.8% loss of its acetylene storage capacity after five cycles of adsorption-desorption tests. Grand canonical Monte Carlo simulation reveals that not only open metal sites but also the suitable pore space and geometry play key roles in its remarkable acetylene uptake.

Stepwise construction of extra-large heterometallic calixarene-based cages.

Utilizing presynthesized large Na2Ni12Ln2 clusters (Ln = Dy and Tb) supported by calixarene as molecular building blocks (MBBs), we have obtained a series of cationic trigonal prismatic heterometallic organic nanocages (HMONCs) with tunable sizes through a stepwise method. Specially, in each structure of the HMONCs, three linear dicarboxylate linkers substitute the peripheral coordinated acetate ligands of two Na2Ni12Ln2 clusters to form an unprecedented Na4Ni24Ln4 HMONC through a M2L3 condensation. Moreover, magnetic study reveals that the Na2Ni12Dy2 core retains its slow magnetic relaxation behavior. Gas sorption behaviors of these HMONCs were also studied. To the best of our knowledge, these HMONCs built from large heterotrimetallic Na2Ni12Ln2 MBBs, which are based on smaller Ni4-calix ones, have not been reported in any other cages to date. In addition, this research also provides a new strategy for the design and construction of HMONCs with predictable structures and functional properties.

Self-assembly of polyhedral indium-organic nanocages.

A synthetic strategy to construct discrete indium-organic polyhedra has been illustrated based on small three-membered windows from a 2,5-pyridinedicarboxylate (PDC) ligand with an angle of 120°. [Et2NH2]6[In6(PDC)12] (InOF-10) is a high-symmetry octahedron with eight three-membered windows, and [Et2NH2]18[In18(BPDC)6(PDC)30] (InOF-11) is a complex polyhedron derived from 3-edge-removed octahedra with an auxiliary biphenyl-3,3'-dicarboxylate (BPDC) ligand. Moreover, the sorption behavior of the latter is also well investigated.

Heterometallic cluster-based indium-organic frameworks.

With the help of the ligand-oriented method, we have successfully embedded independent copper-based units into the indium-organic framework system for the first time, in which the Cu4I4 clusters and In3O(CO2)6 clusters coexist. This heterometallic cluster-based framework has a large porosity with extra-open channels along the c-axis, and its sorption capacity has also been investigated.

Coexistence of cages and one-dimensional channels in a porous MOF with high H(2) and CH(4) uptakes.

A porous metal-organic framework with high surface area was designedly synthesized, in which polyhedral cages and one-dimensional channels coexist. It shows a total gravimetric H2 uptake of 11.35 wt% at 77 K and 90 bar and a total CH4 uptake of 305.07 cm(3) g(-1) at 298 K and 35 bar.

Unusual pore structure and sorption behaviour in a hexanodal zinc-organic framework material.

A highly porous metal-organic framework structurally consists of three topological kinds of 3-connected 1,3,5-benzenetricarboxylate ligands, Zn2(COO)4, Zn3O(COO)6 and Zn4O(COO)6 SBUs, featuring a new 3,3,3,4,4,6-c hexanodal topology. Sorption behaviour in this complicated microporous MOF material has also been investigated.