Introduction of functionality, selection of topology, and enhancement of gas adsorption in multivariate metal-organic framework-177

Controllable synthesis of carbon encapsulated iron phosphide nanoparticles for the chemoselective hydrogenation of aromatic nitroarenes to anilines

Iron phosphide nanoparticles encapsulated in a doped carbon matrix showed high activity and good selectivity in the hydrogenation of aromatic nitroarenes to anilines.

Synthesis and functionalization of phase-pure NU-901 for enhanced CO2adsorption: the influence of a zirconium salt and modulator on the topology and phase purity

Phase-pure NU-901 was functionalized with amines through solvent-assisted linker incorporation resulting in more than double the typical CO₂adsorption capacity.

TopoFF: MOF structure prediction using specifically optimized blueprints

Using topoFF, topological blueprints can be optimized for the structure prediction of MOFs.

Utilizing an effective framework to dye energy transfer in a carbazole-based metal–organic framework for high performance white light emission tuning

By introducing dyes into a MOF, a white-light-emitting luminophor was obtained based on effective framework to dye energy transfer mechanism.

Solvent-induced framework-interpenetration isomers of Cu MOFs for efficient light hydrocarbon separation

For a pair of Cu-paddlewheel framework-interpenetrating isomers, the interpenetrating framework exhibits a high adsorption and separation selectivity for light hydrocarbons.

Selective high adsorption capacity for Congo red dye of a new 3D supramolecular complex and its magnetic hybrid

A new pentacoordinated Cd(ii)-CP based on a flexible nitrogen donor ligand (L) and a corresponding core–shell magnetic Fe₃O₄@SiO₂-NH₂@Cd(ii)-CP hybrid have been synthesized by ultrasonic irradiation. The products can be proposed as good recyclable adsorbents for the selective adsorption of Congo red dye.

Thiophene insertion for continuous modulation of the photoelectronic properties of triphenylamine-based metal–organic frameworks for photocatalytic sulfonylation–cyclisation of activated alkenes

Ligand-engineering through the insertion of thiophenes precisely modulates the photoelectronic properties of metal–organic frameworks for efficient and diastereoselective photocatalytic sulfonylation–cyclisation of activated alkenes.

High-Throughput Computational Screening of Multivariate Metal-Organic Frameworks (MTV-MOFs) for CO2 Capture

Multivariate metal-organic frameworks (MTV-MOFs) contain multiple linker types within a single structure. Arrangements of linkers containing different functional groups confer structural diversity and surface heterogeneity and result in a combinatorial explosion in the number of possible structures. In this work, we carried out high-throughput computational screening of a large number of computer-generated MTV-MOFs to assess their CO₂ capture properties using grand canonical Monte Carlo simulations. The results demonstrate that functionalization enhances CO₂ capture performance of MTV-MOFs when compared to their parent (unfunctionalized) counterparts, and the pore size plays a dominant role in determining the CO₂ adsorption capabilities of MTV-MOFs irrespective of the combinations of the three functional groups (-F, -NH₂, and -OCH₃) that we investigated. We also found that the functionalization of parent MOFs with small pores led to larger enhancements in CO₂ uptake and CO₂/N₂ selectivity than functionalization in larger-pore MOFs. Free energy contour maps are presented to visually compare the influence of linker functionalization between frameworks with large and small pores.

Kinetic-Controlled Formation of Bimetallic Metal-Organic Framework Hybrid Structures

Heterometallic metal-organic frameworks (MOFs) are constructed from two or more kinds of metal ions, while still remaining their original topologies. Due to distinct reaction kinetics during MOF formation, partial distribution of different metals within a single MOF crystal can lead to sophisticated heterogeneous nanostructures. Here, this study reports an investigation of reaction kinetics for different metal ions in a bimetallic MOF system, the ZIF-8/67 (M(2-mIM)₂ , M = Zn for ZIF-8, and Co for ZIF-67, 2-mIM = 2-methylimidazole), by in situ optical method. Distinct kinetics of the two metals forming single-component MOFs are revealed, and when both Co and Zn ions are present in the starting solution, homogeneous distributions of the two metals are only achieved at high Co/Zn ratio, while at low Co/Zn ratio concentration gradient from Co-rich cores to Zn-rich shells is observed. Further, by adding the two metals in sequence, more sophisticated structures are achieved. Specifically, when Co²⁺ is added first, ZIF-67@ZIF-8/67 core-shell nanocrystals are achieved with tunable core/shell thickness ratio depending on the time intervals; while when Zn²⁺ is added first, only agglomerates of irregular shape form due to the weak nucleation ability of Zn²⁺ .

Recent advances in metal-organic frameworks and covalent organic frameworks for sample preparation and chromatographic analysis

In the field of analytical chemistry, sample preparation and chromatographic separation are two core procedures. The means by which to improve the sensitivity, selectivity and detection limit of a method have become a topic of great interest. Recently, porous organic frameworks, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have been widely used in this research area because of their special features, and different methods have been developed. This review summarizes the applications of MOFs and COFs in sample preparation and chromatographic stationary phases. The MOF- or COF-based solid-phase extraction (SPE), solid-phase microextraction (SPME), gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) methods are described. The excellent properties of MOFs and COFs have resulted in intense interest in exploring their performance and mechanisms for sample preparation and chromatographic separation.

Pillared-Layer Metal-Organic Frameworks for Improved Lithium-Ion Storage Performance

Recently, more and more metal-organic frameworks (MOFs) have been directly used as anodic materials in lithium-ion batteries, but judicious design or choice of MOFs is still challenging for lack of structural-property knowledge. In this article we propose a pillared-layer strategy to achieve improved Li-storage performance. Four Mn(II) and Co(II) MOFs with mixed azide and carboxylate ligands were studied to illustrate the strategy. In these 3D MOFs, layers (1, 3, and 4) or chains (2) with short bridges are linked by long organic spacers. All the MOFs show very high lithiation capacity (1170-1400 mA h g^-1 at 100 mA g^-1) in the first cycle owing to the rich insertion sites arising from the azide ion and the aromatic ligands. After the formation cycles, the reversible capacities of the anodes from 1, 3, and 4 are kept at a high level (580-595 mA h g^-1) with good rate and cycling performance, while the anode from 2 undergoes a dramatic drop in capacity. All the MOFs lose the crystallinity after the first cycle. While the amorphization of the chain-based framework of 2 leads to major irreversible deposit of Li ions, the amorphous phases derived from the pillared-layer frameworks of 1, 3, and 4 still retain rich accessible space for reversible insertion and diffusion of active Li ions. Consistent with the analysis, electrochemical impedance spectra revealed that the pillared-layer MOFs led to significantly smaller charge-transfer resistances than 2. Soft X-ray absorption spectroscopy suggested that no metal conversion is involved in the lithiation process, consistent with the fact that the isomorphous Co(II) (3) and Mn(II) (4) MOFs are quite similar in anodic performance.

Lattice-Gas Modeling of Adsorbate Diffusion in Mixed-Linker Zeolitic Imidazolate Frameworks: Effect of Local Imidazolate Ordering

The rates of adsorbate diffusion in zeolitic imidazolate frameworks (ZIFs) can be varied by several orders of magnitude by incorporating two different imidazolate linkers in the ZIF crystals. Although some prior measurements of short-range order in these mixed-linker materials have been reported, it is unclear how this short-range order impacts the net diffusion of adsorbates. We introduce a lattice diffusion model that treats diffusion in ZIF-8_x-90_100-x crystals as a series of activated hops between cages, allowing us to assess the effects of short-range imidazolate order on molecular diffusion.

An efficient combination of Zr-MOF and microwave irradiation in catalytic Lewis acid Friedel-Crafts benzoylation

A zirconium-based metal-organic framework, an effective heterogeneous catalyst, has been developed for the Friedel-Crafts benzoylation of aromatic compounds under microwave irradiation. Constructed by a Zr(iv) cluster and a linker 1,4-bis(2-[4-carboxyphenyl]ethynyl)benzene (H2CPEB), the MOF, possessing large pores and high chemical stability, was appropriate for the enhancement of Lewis acid activity under microwave irradiation. The reaction studies demonstrated that the material could give high yields for a few minutes and maintain its reactivity and structure over several cycles.

Effect of chemical structure of S-nitrosothiols on nitric oxide release mediated by the copper sites of a metal organic framework based environment

The effect of chemical structure of different biologically compatible S-nitrosothiols on the solvation environment at catalytic copper sites in a metal organic framework (MOF) suspended in a solution of ethanol is probed using computational methods. The use of a copper based MOF as a storage vehicle and catalyst (copper sites of the MOF) in the controlled and sustained release of chemically stored nitric oxide (NO) from S-nitrosocysteine has been shown to occur both experimentally and computationally [J. Am. Chem. Soc., 2012, 134, 3330-3333; Phys. Chem. Chem. Phys., 2015, 17, 23403]. Previous studies on a copper based MOF, namely HKUST-1, concluded that modifications in the R-group of s-nitrosothiols and/or organic linkers of MOFs led to a method capable of modulating NO release. In order to test the hypothesis that larger R-groups slow down NO release, four different RSNOs (R = cysteine, N-acetylcysteine, N-acetyl-d,l-penicillamine or glutathione) of varying size were investigated, which in turn required the use of a larger copper based MOF. Due to its desirable copper centers and more extensive framework, MOF-143, an analog of HKUST-1 was chosen to further explore both the effect of different RSNOs as well as MOF environments on NO release. Condensed phase classical molecular dynamics simulations are utilized to study the effect of the complex MOF environment as well as the chemical structure and size of the RSNO on the species on the catalytic reaction. The results indicate that in addition to the size of the RSNO species and the organic linkers within the MOF, the reaction rates can be modulated by the molecular structure of the RSNO and furthermore combining different RSNO species can also be used to tune the rate of NO release.

Sequence-Dependent Materials

Sequence-dependent materials are a class of materials in which a compositionally aperiodic apportionment of functional groups leads to properties where the whole performs better than the sum of the parts. Here, we discuss what defines a sequence-dependent material, and how the concept can be realized in crystals of extended structures such as metal-organic frameworks.

Metal–organic frameworks with 1,4-di(1H-imidazol-4-yl)benzene and varied carboxylate ligands for selectively sensing Fe(iii) ions and ketone molecules

Zn(ii) and Cd(ii) frameworks have potential for sensing Fe(iii) and ketone molecules with high selectivity and sensitivity.

Five 1D to 3D Zn(ii)/Mn(ii)-CPs based on dicarboxyphenyl-terpyridine ligand: stepwise adsorptivity and magnetic properties

Five coordination polymers with different dimensional structures have been solvothermally synthesized by utilizing H₂dtp ligand. Complexes1and2reveal strong solid-state luminescence, and complexes3–5display antiferromagnetic exchange.

Directed assembly of a high surface area 2D metal–organic framework displaying the augmented “kagomé dual” (kgd-a) layered topology with high H2and CO2uptake

A high surface area layered MOF withkgd-atopology, based on a nanosized and highly aromatic hexagonal linker, shows high H₂and CO₂uptake.

Emerging Multifunctional Metal-Organic Framework Materials

Metal-organic frameworks (MOFs), also known as coordination polymers, represent an interesting type of solid crystalline materials that can be straightforwardly self-assembled through the coordination of metal ions/clusters with organic linkers. Owing to the modular nature and mild conditions of MOF synthesis, the porosities of MOF materials can be systematically tuned by judicious selection of molecular building blocks, and a variety of functional sites/groups can be introduced into metal ions/clusters, organic linkers, or pore spaces through pre-designing or post-synthetic approaches. These unique advantages enable MOFs to be used as a highly versatile and tunable platform for exploring multifunctional MOF materials. Here, the bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine.

Seven Post-synthetic Covalent Reactions in Tandem Leading to Enzyme-like Complexity within Metal-Organic Framework Crystals

The design of enzyme-like complexity within metal-organic frameworks (MOFs) requires multiple reactions to be performed on a MOF crystal without losing access to its interior. Here, we show that seven post-synthetic reactions can be successfully achieved within the pores of a multivariate MOF, MTV-IRMOF-74-III, to covalently incorporate tripeptides that resemble the active sites of enzymes in their spatial arrangement and compositional heterogeneity. These reactions build up H2N-Pro-Gly-Ala-CONHL and H2N-Cys-His-Asp-CONHL (where L = organic struts) amino acid sequences by covalently attaching them to the organic struts in the MOFs, without losing porosity or crystallinity. An enabling feature of this chemistry is that the primary amine functionality (-CH2NHBoc) of the original MOF is more reactive than the commonly examined aromatic amines (-NH2), and this allowed for the multi-step reactions to be carried out in tandem within the MOF. Preliminary findings indicate that the complexity thus achieved can affect reactions that were previously accomplished only in the presence of enzymes.

Synthesis, crystal structures, and thermal and spectroscopic properties of two Cd(II) metal-organic frameworks with a versatile ligand

Two new metal-organic frameworks, namely, [Cd(L)(H2O)] n (1) and {[Cd0.5(L)(4,4′-bipy)0.5][Cd0.5(H2O)(4,4′-bipy)0.5]·H2O} n (2), where H2L = N-pyrazinesulfonyl-glycine and 4,4′-bipy = 4,4′-bipyridine, have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental, thermogravimetric, and photoluminescent analysis. X-ray diffraction crystallographic analyses indicate that 1 displays a distorted octahedral metal coordination in a 3-connected (4, 82) topology, while the molecular structure of 2 has a 4-connected (4, 4) topology with two perfectly octahedrally coordinated Cd centers. The L2– ligand serves as a N,N,O-tridentate, μ 2-pyrazine-bridging, and μ 2-carboxylate-bridging ligand in 1, and as a N,O-bidentate and μ 2-carboxylate-bridging ligand in 2. In the crystal, a 3D supramolecular architecture is formed by O–H···O hydrogen bond interactions in 1, but through O–H···O as well as π···π stacking in 2. The two compounds show intense fluorescence in the solid state at room temperature.