Multicomponent Self-Assembly of a Nested Co24@Co48 Metal-Organic Polyhedral Framework

Synergistic Effects of Lewis Acid-Base Pair Sites─Hf-MOFs with Functional Groups as Distinguished Catalysts for the Cycloaddition of Epoxides with CO2

The incorporation of Lewis acid-base sites in catalysts has been considered as a significant approach to fabricating bifunctional catalysts with efficient catalytic activity for CO₂ fixation. In this paper, a series of Hafnium-based metal-organic frameworks (Hf-MOFs), NU-912(Hf) and NU-912-X(Hf)-X (X = -NH₂, -Br, -CN, and -I) derivatives assembled by Lewis acidic Hf₆(μ₃-O)₄(μ₃-OH)₄(H₂O)₄(OH)₄ (Hf₆) clusters and Lewis base-attached organic linkers, are successfully synthesized by a facile ligand functionalization method. These isostructural Hf-MOFs, which exhibit diamond channels of 1.3 nm diameter, great chemical stability, and CO₂ adsorption capacity, have been evaluated as catalysts for the CO₂ cycloaddition reaction with epoxides. Catalytic experiments reveal that the micropore environments of these MOFs have an outstanding impact on catalytic activity. Remarkably, NU-912(Hf)-I serves as an efficient heterogeneous catalyst for this catalytic reaction under mild conditions due to the high density of Lewis acid Hf₆ cluster centers and strong Lewis base functional groups, surpassing most of the reported MOF-based catalysts.

Designed assembly of heterometallic zeolite-like framework materials from two different supertetrahedral metal clusters

This work demonstrates a feasible strategy for the synthesis of new zeolite-like framework materials. With the strategy of using two different supertetrahedral clusters as secondary building units, two new heterometallic zeolite-like frameworks with isomeric structures but tunable topologies were first made. Besides, the porous nature and the proton conduction performance of the new materials were further studied.

Sodalite Cd66-Cage-Based Metal-Organic Framework Constructed by Cd9 and Cd5 Metal-Organic Clusters

A sodalite Cd₆₆-cage-based metal-organic framework (MOF), namely, CPM-9S, has been constructed based on Cd₉ and Cd₅ metal-organic clusters (MOCs), which, to the best our knowledge, represents the first Cd-cage-based MOF that contains the highest-nuclear Cd-based MOC and the largest number of Cd²⁺ ions in a cage. The iodine adsorption performances in terms of the iodine adsorption capacity, adsorption isotherm, and adsorption kinetics, as well as the adsorption mechanism, have been further studied.

Morphology-Dependent Peroxidase Mimicking Enzyme Activity of Copper Metal-Organic Polyhedra Assemblies

The morphology of nanomaterials (geometric shape and dimension) play a significant role in its various physical and chemical properties. Thus, it is essential to link morphology with performance in specific applications. For this purpose, the morphology of copper metal-organic polyhedra (Cu-MOP) can be modulated through distinct assembly process, which facilitates the exploration of the relationship between morphology and catalytic performance. In this work, the assemblies of Cu-MOP with three different morphologies (nanorods, nanofibers and nanosheets) were facilely prepared by the variation of solvent mixture of N, N-dimethylformamide (DMF) and methanol, revealed the important role of the interaction between the surface group and the solvent on the morphology of these assemblies. Cu-MOP nanofibers exhibited the highest mimetic peroxidase enzyme activity over the Cu-MOP nanosheets and nanorods, which have been utilized in the detection of glucose. Cu-MOPs assemblies with tunable morphology accompanied with adjustable mimic peroxidase activity, had great potential applications in the field of bioanalytical chemistry and biomedicals.

Double-Walled Zn36@Zn104 Multicomponent Senary Metal-Organic Polyhedral Framework and Its Isoreticular Evolution

Metal-organic polyhedral frameworks are attractive in gas storage and separation due to large voids with windows that can serve as traps for guest molecules. Introducing multivariant/multicomponent functionalities in them are ways of improving performances for certain targets. The high compatibility of organic linkers can generate multivariant MOFs, but by far, the diversity of secondary building units (SBUs) in a single metal-organic framework is still limited (no more than two in most cases). Here we report a new double-walled Zn₃₆@Zn₁₀₄ metal-organic polyhedral framework (HHU-8) with five types of topologically distinct SBUs and its isoreticular evolution to the Zn₃₆@Zn₁₃₆ counterpart (HHU-8s). Both MOFs are the first to be constructed with such high numbers of topologically distinct SBUs as well as topologically distinct nodes, and their formation and evolution provide new insight into SBU's controllability.

Ultrastable High-Connected Chromium Metal-Organic Frameworks

State-of-the-art MOFs are generally known for chemical stability at one end of the pH scale (i.e., pH < 0 or pH > 14). Herein, we report new Cr-MOFs capable of withstanding extreme pH conditions across approximately 16 pH units from pH < 0 to pH > 14, likely the largest observed pH range for MOFs. The integration of multiple stability-enhancing factors including nonlabile Cr³⁺, mixed Cr-N and Cr-O cross-links, and the highest possible connectivity by Cr₃O trimers enables extraordinary chemical stability confirmed by both PXRD and gas adsorption. Notably, the base stability is much higher than literature Cr-MOFs, thereby revitalizing Cr-MOF's viability in the pursuit for the most chemically stable MOFs. Among known cationic MOFs, the chemical stability of these new Cr-MOFs is unmatchable, to our knowledge. These Cr-MOFs can be developed into multiseries of isoreticular MOFs with a rich potential for functionalization, pore size, and pore geometry engineering and applications.

Metal-Organic Frameworks and Metal-Organic Gels for Oxygen Electrocatalysis: Structural and Compositional Considerations

Increasing demand for sustainable and clean energy is calling for the next-generation energy conversion and storage technologies such as fuel cells, water electrolyzers, CO₂ /N₂ reduction electrolyzers, metal-air batteries, etc. All these electrochemical processes involve oxygen electrocatalysis. Boosting the intrinsic activity and the active-site density through rational design of metal-organic frameworks (MOFs) and metal-organic gels (MOGs) as precursors represents a new approach toward improving oxygen electrocatalysis efficiency. MOFs/MOGs afford a broad selection of combinations between metal nodes and organic linkers and are known to produce electrocatalysts with high surface areas, variable porosity, and excellent activity after pyrolysis. Some recent studies on MOFs/MOGs for oxygen electrocatalysis and their new perspectives in synthesis, characterization, and performance are discussed. New insights on the structural and compositional design in MOF/MOG-derived oxygen electrocatalysts are summarized. Critical challenges and future research directions are also outlined.

Equi-size nesting of Platonic and Archimedean metal-organic polyhedra into a twin capsid

Inspired by the structures of virus capsids, chemists have long pursued the synthesis of their artificial molecular counterparts through self–assembly. Building nanoscale hierarchical structures to simulate double-shell virus capsids is believed to be a daunting challenge in supramolecular chemistry. Here, we report a double-shell cage wherein two independent metal–organic polyhedra featuring Platonic and Archimedean solids are nested together. The inner (3.2 nm) and outer (3.3 nm) shells do not follow the traditional “small vs. large” pattern, but are basically of the same size. Furthermore, the assembly of the inner and outer shells is based on supramolecular recognition, a behavior analogous to the assembly principle found in double-shell viruses. These two unique nested characteristics provide a new model for Matryoshka–type assemblies. The inner cage can be isolated individually and proves to be a potential molecular receptor to selectively trap guest molecules.

Supramolecular constructs that mimic complex biological assemblies are synthetically challenging. Here, the authors present a double-shell cage wherein two independent metal-organic polyhedra are nested together in a manner analogous to that found in double-shell virus capsids.

A 116-Nuclear Metallosupramolecular Cage-of-Cage Showing Multistep Single-Crystal-to-Single-Crystal Transformation

Here a unique single-crystal-to-single-crystal (SCSC) transformation of a 116-nuclear Au^I ₇₂ Cd^II ₄₀ Na^I ₄ cage-of-cage (2_CdNa ) is reported, which was created from a trigold(I) metalloligand with d-penicillamine by way of a 9-nuclear Au^I ₆ Cd^II ₃ cage (1). Cage-of-cage 2_CdNa is composed of 12 cages of 1 that are linked by 4 Cd²⁺ and 4 Na⁺ ions, with its surface being covered by 12 NO₃ ^- ions to form a discrete, spherical molecule with a diameter ca. 4.7 nm. In crystal 2_CdNa , the cage-of-cage molecules are packed in a cubic lattice with a huge cell volume of ca. 4.5×10⁵  ų _, so as to have large interstices with diameters of more than 3 nm. Upon soaking crystals 2_CdNa in aqueous Cu(NO₃ )₂ , all Cd²⁺ and Na⁺ were quickly exchanged by Cu²⁺ to produce an analogous Au^I ₇₂ Cu^II ₄₄ cage-of-cage (2_Cu ) in a SCSC manner. Prolonged soaking led to the SCSC transformation to another supramolecular structure (2'_Cu ) consisting of 152-nuclear Au^I ₇₂ Cu^II ₈₀ cage-of-cages that are alternately H-bonded with the Au^I ₇₂ Cu^II ₄₄ cage-of-cages. 2'_Cu showed the accommodation of MoO₄ ^2- and the conversion of MoO₄ ^2- to β-Mo₈ O₂₆ ^4- in the crystal, with retention of single-crystallinity.

Polyoxometalate–viologen photochromic hybrids for rapid solar ultraviolet light detection, photoluminescence-based UV probing and inkless and erasable printing

Polyoxometalate–viologen photochromic hybrids showed efficient and fast low intensity ultraviolet light detection, potential fluorescence based UV probing and inkless and erasable printing.

Two Novel Polyoxometalate-Encapsulated Metal-Organic Nanotube Frameworks as Stable and Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction

Two novel polyoxometalate (POM)-encapsulated metal-organic nanotube (MONT) framework crystalline materials with unprecedented copper-mixed ligands, HUST-200 and HUST-201, have been successfully synthesized by an effective synthesis strategy. The encapsulation not only provides a shield to increase the chemical stability, but also does not affect its catalytic activity, and, therefore, the crystalline materials are very active for HER (H⁺ can diffuse easily through the pores of the MONTs). Remarkably, HUST-200 displays a low overpotential of 131 mV (catalytic current density is equal to 10 mA·cm^-2). This work thus offers a new way for devising HER electrocatalysts with low cost using POM-encapsulated MONT frameworks.

Binder driven self-assembly of metal-organic cubes towards functional hydrogels

The process of assembling astutely designed, well-defined metal-organic cube (MOC) into hydrogel by using a suitable molecular binder is a promising method for preparing processable functional soft materials. Here, we demonstrate charge-assisted H-bonding driven hydrogel formation from Ga³⁺-based anionic MOC ((Ga₈(ImDC)₁₂)¹²⁻) and molecular binders, like, ammonium ion (NH₄⁺), N-(2-aminoethyl)-1,3-propanediamine, guanidine hydrochloride and β-alanine. The morphology of the resulting hydrogel depends upon the size, shape and geometry of the molecular binder. Hydrogel with NH₄⁺ shows nanotubular morphology with negative surface charge and is used for gel-chromatographic separation of cationic species from anionic counterparts. Furthermore, a photo-responsive luminescent hydrogel is prepared using a cationic tetraphenylethene-based molecular binder (DATPE), which is employed as a light harvesting antenna for tuning emission colour including pure white light. This photo-responsive hydrogel is utilized for writing and preparing flexible light-emitting display.

A possible route to producing processable soft materials is by assembling metal organic cubes into hydrogels. Here the authors show charge-assisted H-bond driven self-assembly of Ga³⁺-based anionic metal organic cubes and suitable molecular binders towards multi-functional hydrogels.

Hierarchical Assembly of a {Co24} Cluster from Two Vertex-Fused {Co13} Clusters and Their Single-Molecule Magnetism

We present the synthesis, structural characterization, and magnetic properties of two high-nuclearity cobalt clusters formulated as [Co₁₃(μ₃-OH)₃(μ₃-Cl)(dpbt)₅(ptd)Cl₁₀][Co(H₂O)₂Cl₂]·(CH₃)₂CHOH (1) and [Co₂₄(μ₃-OH)₆(μ₃-Cl)₂(dpbt)₁₀(ptd)₂Cl₁₆]·2CH₃CH₂OH (2), respectively (H₂dpbt = 5,5'-bis(pyridin-2-yl)-3,3'-bis(1,2,4-triazole) and H₂ptd = 3-(pyridin-2-yl)-1,2,4-triazine-5,6-diol). Compound 1 is composed of an inner [Co₄(μ₃-OH)₃(μ₃-Cl)] cubane and an outer [Co₉(dpbt)₅(ptd)Cl₁₀] defective adamantane. Compound 2 reveals a giant {Co₂₄} cluster possessing a dual-[Co₁₂] skeleton from 1. The hierarchical assembly from 1 to 2 has been established and tracked through high-resolution electrospray ionization (HRESI-MS) analyses from the solvothermal reaction mother solution. Magnetic studies of 1 and 2 revealed the highly correlated spins, a glasslike magnetic phase transition at ca. 8 K, and slow relaxation behavior of SMM nature in the lower-temperature region (below 4 K).

The influence of the secondary building linker geometry on the photochromism of naphthalenediimide-based metal–organic frameworks

The photochromism of three MOFs based on NDI chromophores is mainly induced by two kinds of non-covalent intermolecular interactions.

Enhancing the stability and porosity of penetrated metal-organic frameworks through the insertion of coordination sites

Guided by the insertion of coordination sites within ligands, an interpenetrated metal–organic framework (MOFs) NKU-112 and a self-penetrated framework NKU-113 were obtained. The enhanced stability and porosity of NKU-113 prove the efficiency of the method for the structure and properties modulation of penetrated MOFs.

Guided by the insertion of coordination sites within ligands, an interpenetrated metal–organic framework NKU-112 and a self-penetrated framework NKU-113 were obtained. The two MOFs have similar cage-based framework structures, while NKU-113 reveals enhanced porosity and stability compared with NKU-112, owing to the self-penetrated structure induced by the additional chelating bipyridine moiety in the ligand. To the best of our knowledge, this is the first study that attempts to shift the structure topology of a MOF from interpenetrated to self-penetrated while achieving a delicate modulation of the location and distances within the penetrated structure by inserting new coordination sites.

Pore Space Partition in Metal-Organic Frameworks

Metal-organic framework (MOF) materials have emerged as one of the favorite crystalline porous materials (CPM) because of their compositional and geometric tunability and many possible applications. In efforts to develop better MOFs for gas storage and separation, a number of strategies including creation of open metal sites and implantation of Lewis base sites have been used to tune host-guest interactions. In addition to these chemical factors, the geometric features such as pore size and shape, surface area, and pore volume also play important roles in sorption energetics and uptake capacity. For efficient capture of small gas molecules such as carbon dioxide under ambient conditions, large surface area or high pore volume are often not needed. Instead, maximizing host-guest interactions or the density of binding sites by encaging gas molecules in snug pockets of pore space can be a fruitful approach. To put this concept into practice, the pore space partition (PSP) concept has been proposed and has achieved a great experimental success. In this account, we will highlight many efforts to implement PSP in MOFs and impact of PSP on gas uptake performance. In the synthetic design of PSP, it is helpful to distinguish between factors that contribute to the framework formation and factors that serve the purpose of PSP. Because of the need for complementary structural roles, the synthesis of MOFs with PSP often involves multicomponent systems including mixed ligands, mixed inorganic nodes, or both. It is possible to accomplish both framework formation and PSP with a single type of polyfunctional ligands that use some functional groups (called framework-forming group) for framework formation and the remaining functional groups (called pore-partition group) for PSP. Alternatively, framework formation and PSP can be shouldered by different chemical species. For example, in a mixed-ligand system, one ligand (called framework-forming agent) can play the role of the framework formation while the other type of ligand (called pore-partition agent) can assume the role of PSP. PSP is sensitive to the types of inorganic secondary building units (SBUs). The coexistence of SBUs complementary in charge, connectivity, and so on can promote PSP. The use of heterometallic systems can promote the diversity of SBUs coexistent under a given condition. Heterometallic system with metal ions of different oxidation states also provides the charge tunability of SBUs and the overall framework, providing an additional level of control in self-assembly and ultimately in the materials' properties. Of particular interest is the PSP in MIL-88 type (acs-type topology) structure, which has led to a huge family of CPMs (called pacs CPMs, pacs = partitioned acs) exhibiting low isosteric heat of adsorption and yet superior CO₂ uptake capacity.

Two bilayer metal–organic frameworks with rare trinuclear heterometal clusters and tunable photoluminescence

Two bilayer metal–organic frameworks based on rare trinuclear Pb/K and Cd/Na clusters have been solvothermally synthesized. They exhibit tunable purple-to-red-to-green and purple-to-green photoluminescence by variation of excitation light, respectively.

Synthesis, structure and luminescence properties of two Cd(ii)/M(i) (M = K, Rb) interpenetrated heterometallic frameworks based on giant double-walled cages

Two isostructural 2-fold interpenetrated double-walled frameworks based on a rare heterometallic nested cage-within-cage motif were synthesized.

An electron-transfer photochromic crystalline MOF accompanying photoswitchable luminescence in a host–guest system

A new electron transfer type photoactive host–guest supramolecule was constructed by introducing (CH₃)₂NH₂⁺ cations to the MOF framework. The resulting compound 1 exhibits reversible photochromic property without using photochromic components.

Metalation Triggers Single Crystalline Order in a Porous Solid

We report the dramatic triggering of structural order in a Zr(IV)-based metal-organic framework (MOF) through docking of HgCl₂ guests. Although as-made crystals were unsuitable for single crystal X-ray diffraction (SCXRD), with diffraction limited to low angles well below atomic resolution due to intrinsic structural disorder, permeation of HgCl₂ not only leaves the crystals intact but also resulted in fully resolved backbone as well as thioether side groups. The crystal structure revealed elaborate HgCl₂-thioether aggregates nested within the host octahedra to form a hierarchical, multifunctional net. The chelating thioether groups also promote Hg(II) removal from water, while the trapped Hg(II) can be easily extricated by 2-mercaptoethanol to reactivate the MOF sorbent.

The First Example of Hetero-Triple-Walled Metal-Organic Frameworks with High Chemical Stability Constructed via Flexible Integration of Mixed Molecular Building Blocks

An unprecedented 3D hetero-triple-walled metal-organic framework is obtained by straightforward elaboration of the mixed molecular building block (MBB) strategy. In this approach, multiple individual flexible and rigid MBBs are integrated into one composite building block as separate layers, which are of the same shape but different sizes. This MOF shows exceptional water stability and the application of Li-ion battery electrodes.

Structures of Metal-Organic Frameworks with Rod Secondary Building Units

Rod MOFs are metal-organic frameworks in which the metal-containing secondary building units consist of infinite rods of linked metal-centered polyhedra. For such materials, we identify the points of extension, often atoms, which define the interface between the organic and inorganic components of the structure. The pattern of points of extension defines a shape such as a helix, ladder, helical ribbon, or cylinder tiling. The linkage of these shapes into a three-dimensional framework in turn defines a net characteristic of the original structure. Some scores of rod MOF structures are illustrated and deconstructed into their underlying nets in this way. Crystallographic data for all nets in their maximum symmetry embeddings are provided.

Synthesis, structure and adsorption properties of lanthanide-organic frameworks with pyridine-3,5-bis(phenyl-4-carboxylate)

Under solvothermal conditions, reactions of pyridine-3,5-bis(phenyl-4-carboxylic acid) (H2L) with lanthanide metal salts give rise to three new metal-organic frameworks (MOFs) with the formula {[Ln4(L)3(μ3-OH)4(H2O)4]·(NO3)2·solvent}n [Ln = Er (1), Yb (2) and Lu (3)]. The complexes were characterized by single crystal and powder X-ray diffraction, IR and thermogravimetric analyses. They have the same two-fold interpenetrating three-dimensional (3D) framework structures with [Ln4(COO)6(μ3-OH)4(H2O)4] clusters as secondary building units (SBUs) and a rare 6-connected lcy topology with the point (Schläfli) symbol of {3(3)·5(9)·6(3)}. Interestingly, 1-3 show selective and hysteretic sorption of CO2 over N2, and the photoluminescence properties of the complexes were also investigated.

Construction of a polyhedron decorated MOF with a unique network through the combination of two classic secondary building units

A decorated metal–organic polyhedron based metal–organic framework with a unique 4,9-connected net is constructed, showing relatively strong interaction toward H₂and CO₂probably due to the presence of open metal sites in secondary building units.

Selectivity of CO2via pore space partition in zeolitic boron imidazolate frameworks

Co-assembly between boron imidazolate ligands and bridging dicarboxylate ligands with metal centers leads to pore space partitioning in two distinct BIFs with zeotype GIS (BIF-41) and ABW (BIF-42) topologies, respectively. BIF-41 shows high selectivity sorption of CO₂ over N₂.

Rare double spin canting antiferromagnetic behaviours in a [Co24] cluster

A fish-basket-shaped [Co₂₄] cluster, [Co₂₄(μ₃-O)₄(ampc)₄(μ₃-OH)₄(μ₂-OH)₄(NO₃)₅(HCO₂)₂₂(H₂O)₁₀]·[(HCO₂)·2(CH₃OH)·x(H₂O)], was woven by bridging oxygen atoms from O²⁻, OH⁻, NO₃⁻ and HCO₂⁻ groups, and stabilized terminally by a semi-rigid organic ligand 4′,4′-[(dimethylamino)dimethylene]-bis[(1,1′-biphenyl)-2-carboxylate] (ampc⁻).

"Heterogeneity within order" in metal-organic frameworks

Metal-organic frameworks (MOFs) are constructed by linking inorganic units with organic linkers to make extended networks. Though more than 20 000 MOF structures have been reported most of these are ordered and largely composed of a limited number of different kinds building units, and very few have multiple different building units (heterogeneous). Although heterogeneity and multiplicity is a fundamental characteristic of biological systems, very few synthetic materials incorporate heterogeneity without losing crystalline order. Thus, the question arises: how do we introduce heterogeneity into MOFs without losing their ordered structure? This Review outlines strategies for varying the building units within both the backbone of the MOF and its pores to produce the heterogeneity that is sought after. The impact this heterogeneity imparts on the properties of a MOF is highlighted. We also provide an update on the MOF industry as part of this themed issue for the 150th anniversary of BASF.

A two-dimensional honeycomb coordination network based on fused triacontanuclear heterometallic {Co12Mn18} wheels

An unprecedented two-dimensional honeycomb paramagnetic network based on fused triacontanuclear heterometallic wheels of 3.4 nm, {[Co₂(Mn₃O)(N₃)₂(pic)₆(NO₃)]⁻}₆, has been assembled.