Structures of Metal-Organic Frameworks with Rod Secondary Building Units

Solvent-Free Synthesis of Uniform MOF Shell-Derived Carbon Confined SnO2 /Co Nanocubes for Highly Reversible Lithium Storage

Tin dioxide (SnO₂ ) has attracted much attention in lithium-ion batteries (LIBs) due to its abundant source, low cost, and high theoretical capacity. However, the large volume variation, irreversible conversion reaction limit its further practical application in next-generation LIBs. Here, a novel solvent-free approach to construct uniform metal-organic framework (MOF) shell-derived carbon confined SnO₂ /Co (SnO₂ /Co@C) nanocubes via a two-step heat treatment is developed. In particular, MOF-coated CoSnO₃ hollow nanocubes are for the first time synthesized as the intermediate product by an extremely simple thermal solid-phase reaction, which is further developed as a general strategy to successfully obtain other uniform MOF-coated metal oxides. The as-synthesized SnO₂ /Co@C nanocubes, when tested as LIB anodes, exhibit a highly reversible discharge capacity of 800 mAh g^-1 after 100 cycles at 200 mA g^-1 and excellent cycling stability with a retained capacity of 400 mAh g^-1 after 1800 cycles at 5 A g^-1 . The experimental analyses demonstrate that these excellent performances are mainly ascribed to the delicate structure and a synergistic effect between Co and SnO₂ . This facile synthetic approach will greatly contribute to the development of functional metal oxide-based and MOF-assisted nanostructures in many frontier applications.

A route to robust thioether-functionalized MOF solid materials displaying heavy metal uptake and the ability to be further oxidized

Here we developed a facile solvent-assisted ligand exchange method for synthesizing thioether-containing hybrid metal-organic frameworks (MOFs) that cannot be made using direct synthesis. Such a tailored approach provides an alternative method to achieve thioether-based MOFs and its oxidation-decorated materials. These materials showed the ability to take up heavy metals from solution and the ability to capture CO₂.

Microstructural Engineering and Architectural Design of Metal-Organic Framework Membranes

In the past decade, a huge development in rational design, synthesis, and application of molecular sieve membranes, which typically included zeolites, metal-organic frameworks (MOFs), and graphene oxides, has been witnessed. Owing to high flexibility in both pore apertures and functionality, MOFs in the form of membranes have offered unprecedented opportunities for energy-efficient gas separations. Reports on the fabrication of well-intergrown MOF membranes first appeared in 2009. Since then there has been tremendous growth in this area along with an exponential increase of MOF-membrane-related publications. In order to compete with other separation and purification technologies, like cryogenic distillation, pressure swing adsorption, and chemical absorption, separation performance (including permeability, selectivity, and long-term stability) of molecular sieve membranes must be further improved in an attempt to reach an economically attractive region. Therefore, microstructural engineering and architectural design of MOF membranes at mesoscopic and microscopic levels become indispensable. This review summarizes some intriguing research that may potentially contribute to large-scale applications of MOF membranes in the future.

Multiple Coordination Exchanges for Room-Temperature Activation of Open-Metal Sites in Metal-Organic Frameworks

The activation of open coordination sites (OCSs) in metal-organic frameworks (MOFs), i.e., the removal of solvent molecules coordinated at the OCSs, is an essential step that is required prior to the use of MOFs in potential applications such as gas chemisorption, separation, and catalysis because OCSs often serve as key sites in these applications. Recently, we developed a "chemical activation" method involving dichloromethane (DCM) treatment at room temperature, which is considered to be a promising alternative to conventional thermal activation (TA), because it does not require the application of external thermal energy, thereby preserving the structural integrity of the MOFs. However, strongly coordinating solvents such as N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), and dimethyl sulfoxide (DMSO) are difficult to remove solely with the DCM treatment. In this report, we demonstrate a multiple coordination exchange (CE) process executed initially with acetonitrile (MeCN), methanol (MeOH), or ethanol (EtOH) and subsequently with DCM to achieve the complete activation of OCSs that possess strong extracoordination. Thus, this process can serve as an effective "chemical route" to activation at room temperature that does not require applying heat. To the best of our knowledge, no previous study has demonstrated the activation of OCSs using this multiple CE process, although MeOH and/or DCM has been popularly used in pretreatment steps prior to the TA process. Using MOF-74(Ni), we demonstrate that this multiple CE process can safely activate a thermally unstable MOF without inflicting structural damage. Furthermore, on the basis of in situ ¹H nuclear magnetic resonance (¹H NMR) and Raman studies, we propose a plausible mechanism for the activation behavior of multiple CE.

Addressed realization of multication complex arrangements in metal-organic frameworks

The preparation of materials with structures composed of multiple metal cations that occupy specific sites is challenging owing to the difficulty of simultaneously addressing the incorporation of different elements at desired precise positions. We report how it is possible to use a metal-organic framework (MOF) built with a rod-shaped inorganic secondary building unit (SBU) to combine multiple metal elements at specific positions in a manner that is controllable at atomic and mesoscopic scales. Through the combination of four different metal elements at judiciously selected molar ratios, 20 MOFs of different compositions and the same topology have been prepared and characterized. The use of diffraction techniques, supported by density functional theory calculations, has led us to determine various possible atomic arrangements of the metal cations within the SBUs. In addition, seven of the compounds combine multiple types of atomic arrangements, which are mesoscopically distributed along the crystals. Given the large diversity and importance of rod-based MOFs, we believe that these findings offer a new general strategy to produce complex materials with required compositions and controllable arrangements of the metal cations for desired applications.

Pyrolysis of Helical Coordination Polymers for Metal-Sulfide-Based Helices with Broadband Chiroptical Activity

Fabrication of chiroptical materials with broadband response in the visible light region is vital to fully realize their potential applications. One way to achieve broadband chiroptical activity is to fabricate chiral nanostructures from materials that exhibit broadband absorption in the visible light region. However, the compounds used for chiroptical materials have predominantly been limited to materials with narrowband spectral response. Here, we synthesize Ag₂S-based nanohelices derived from helical coordination polymers. The right- and left-handed coordination helices used as precursors are prepared from l- and d-glutathione with Ag⁺ and a small amount of Cu²⁺. The pyrolysis of the coordination helices yields right- and left-handed helices of Cu_0.12Ag_1.94S/C, which exhibit chiroptical activity spanning the entire visible light region. Finite element method simulations substantiate that the broadband chiroptical activity is attributed to synergistic broadband light absorption and light scattering. Furthermore, another series of Cu_0.10Ag_1.90S/C nanohelices are synthesized by choosing the l- or d-Glu-Cys as starting materials. The pitch length of nanohelicies is controlled by changing the peptides, which alters their chiroptical properties. The pyrolysis of coordination helices enables one to fabricate helical Ag₂S-based materials that enable broadband chiroptical activity but have not been explored owing to the lack of synthetic routes.

Single-Site Cobalt Catalysts at New Zr12(μ3-O)8(μ3-OH)8(μ2-OH)6 Metal-Organic Framework Nodes for Highly Active Hydrogenation of Nitroarenes, Nitriles, and Isocyanides

We report here the synthesis of a robust and porous metal-organic framework (MOF), Zr₁₂-TPDC, constructed from triphenyldicarboxylic acid (H₂TPDC) and an unprecedented Zr₁₂ secondary building unit (SBU): Zr₁₂(μ₃-O)₈(μ₃-OH)₈(μ₂-OH)₆. The Zr₁₂-SBU can be viewed as an inorganic node dimerized from two commonly observed Zr₆ clusters via six μ₂-OH groups. The metalation of Zr₁₂-TPDC SBUs with CoCl₂ followed by treatment with NaBEt₃H afforded a highly active and reusable solid Zr₁₂-TPDC-Co catalyst for the hydrogenation of nitroarenes, nitriles, and isocyanides to corresponding amines with excellent activity and selectivity. This work highlights the opportunity in designing novel MOF-supported single-site solid catalysts by tuning the electronic and steric properties of the SBUs.

A sandwich-shaped M3L2 zinc(ii) complex containing 1,3,5-tris(dimethyl(pyridin-3-yl)silyl)benzene: selective photoluminescence recognition of diiodomethane

Self-assembly of Zn(ClO₄)₂ with 1,3,5-tris(dimethyl(pyridin-3-yl)silyl)benzene (L) as a new C₃-symmetric tridentate N-donor gives rise to a discrete sandwich-shaped M₃L₂ architecture, [Zn₃(μ-OH)₃L₂](ClO₄)₃·4CH₃CN·2H₂O. Its blue photoluminescence is significantly quenched only by CH₂I₂ among the various small molecules, CH₂Cl₂, CH₂Br₂, CHCl₃, 1,2-dichloroethane, EtOH, CH₃CN, benzene, toluene, and phenol.

Directed adenine functionalization for creating complex architectures for material and biological applications

In this feature article, targeted design strategies are outlined for modified adenine nucleobase derivatives in order to construct metal-mediated discrete complexes, ring-expanded purine skeletons, linear and catenated coordination polymers, shape-selective MOFs, and purine-capped nanoparticles, with a wide range of applications from gas and solvent adsorption to bioimaging agents and anticancer metallodrugs. The success of such design strategies could be ascribed to the rich chemistry of purine and pyrimidine derivatives, versatile coordination behavior, ability to bind a host of metal ions, which could be further tuned by the introduction of additional functionalities, and their inherent propensity to hydrogen bond and exhibit π-π interactions. These noncovalent interactions produce stable frameworks and network solids that are useful as advanced materials, and the biocompatibility of these ligand complexes provides an impetus for assessing novel biological applications.

A Homochiral Multifunctional Metal-Organic Framework with Rod-Shaped Secondary Building Units

A new homochiral multifunctional metal-organic framework, [Zn₂(CTBA)₂·H₂O] (JUC-112), was synthesized under solvothermal conditions, through the design of chiral ligand 4-(3-carboxy-2,2,3-trimethylcyclopentanecarboxamido) benzoic acid (H₂CTBA) based on camphoric acid as building block. The crystal structure of the new material is a 2-dimensional (2D) chiral layer packed with infinite rod-shaped secondary building units (SBUs). The homochiral framework was identified by circular dichroism (CD) spectrum. Thermogravimetric measurement indicates its high thermal stability up to 450 °C. In addition, JUC-112 exhibits the capability of separating water from alcohols, second-order nonlinear optical effect, and photoluminescence.

Enantiomeric two-fold interpenetrated 3D zinc(ii) coordination networks as a catalytic platform: significant difference between water within the cage and trace water in transesterification

Self-assembly of Zn(ClO₄)₂ with 1,1,2,2-tetramethyl-1,2-di(pyridin-3-yl)disilane (L) as a bidentate N-donor gives rise to 3D coordination networks, [Zn(μ-OH)(L)]₃(ClO₄)₃·5H₂O (1·5H₂O), of unique, 10³-a srs net topology. An important feature is that two enantiomeric 3D frameworks, 4¹- and 4³-[Zn(μ-OH)(L)]₃(ClO₄)₃·5H₂O, are interpenetrated to form a racemic two-fold 3D network with cages occupied by two water molecules. Another structural characteristic is a C₃-symmetric planar Zn₃(μ-OH)₃ 6-membered ring with tetrahedral Zn(ii) ions. The steric hindrance of substrates and trace water effects on transesterification catalysis using the network have been scrutinized. The coordination network acts as a remarkable heterogeneous transesterification catalytic system that shows both the significant steric effects of substrate alcohols and momentous water effects. The substrate activity is in the order ethanol > n-propanol > n-butanol > iso-propanol > 2-butanol > tert-butanol. For the reaction system, solvate water molecules within the cages of the interpenetrated 3D frameworks do not decrease the transesterification activity, whereas the trace water molecules in the substrate alcohols act as obvious obstacles to the reaction.

Crystal structure of poly[[aqua-(μ-2,3-di-hydro-thieno[3,4-b][1,4]dioxine-5,7-di-carboxyl-ato-κ2O5:O7)[μ-di(pyridin-4-yl)sulfane-κ2N:N']zinc] 0.26-hydrate]

The crystal structure of the title polymer, {[Zn(C8H4O6S)(C10H8N2S)(H2O)]·0.26H2O} n , is characterized by a layered arrangement parallel to the ab plane. The zinc cation is five-coordinated in a slightly distorted trigonal-bipyramidal coordination environment defined by two pyridine ligands, two carboxyl-ate groups of two thio-phene di-carboxyl-ate ligands, and by one water mol-ecule. The ethyl-ene bridge in the dioxine ligand is disordered over two sets of sites [occupancy ratio 0.624 (9):0.376 (9)]. Several hydrogen-bonding inter-actions of the types O-H⋯O, C-H⋯O, C-H⋯S and C-H⋯N ensure the cohesion within the crystal structure.

A Fluorescent Anionic MOF with Zn4(trz)2 Chain for Highly Selective Visual Sensing of Contaminants: Cr(III) Ion and TNP

Heavy-metal ions and nitroaromatic substances are highly toxic and harmful to human health and the ecological environment. It is an urgent issue to selectively detect and capture these toxic substances. By introducing the triazole ligand to the π-conjugated aromatic carboxylate system and borrowing the organic template open framework idea, a stable fluorescent framework [Me₂NH₂]₄[Zn₆(qptc)₃(trz)₄]·6H₂O (1) (H₄qptc = terphenyl-2,5,2'5'-tetracarboxylic acid, trz = 1,2,4-triazole) has been successfully synthesized, which features Zn₄(trz)₂ chain-based 3D anionic structure with channels filled by [Me₂NH₂]⁺ cations. It is worth noting that the material exhibits selective adsorption and recyclable detection of heavy-metal Cr³⁺ ion in aqueous solutions, which may be the synergy from the metal charge, bond ability of metal ions to carboxylate oxygen atom, and soft-hard acid-base properties. Furthermore, it can selectively sense of 2,4,6-trinitrophenol with a large quenching coefficient K_sv of 2.08 × 10⁶ M^-1.

Highly Water-Stable Novel Lanthanide Wheel Cluster Organic Frameworks Featuring Coexistence of Hydrophilic Cagelike Chambers and Hydrophobic Nanosized Channels

In attempts to investigate the potential luminescent sensing materials for sensitive detection of environmental pollutants, a new family of lanthanide wheel cluster organic frameworks (Ln-WCOFs) UJN-Ln4 has been constructed by employing one of the cycloalkane dicarboxylic acid derivatives. Adopting different conformations, the ligand links Ln₄ second building units (SBUs) and Ln₂₄ tertiary building units (TBUs) to form a unique wheel cluster layer-pillared 3D framework featuring the coexistence of hydrophobic nanosized channels and trigonal antiprism arrays with hydrophilic cagelike chambers. Apart from charming structures, isostructural UJN-Ln4 displays interesting porous, water-stable features. Systematic luminescence studies demonstrate that solvent water molecules can enhance the emission intensity of solid-state UJN-Eu4. Acting as a recyclable luminescent probe, water-stable luminescent UJN-Eu4 exhibits superior "turn-off" detection for Fe³⁺ and Cu²⁺ ions in aqueous solutions. Due to the nanosized hydrophobic channels, UJN-Eu4 also shows highly sensitive sensing of sodium dodecyl benzenesulfonate (SDBS) via luminescence "turn-on" respondence, representing the first example of quantitatively detecting SDBS in aqueous solutions by employing luminescent lanthanide frameworks as fluorescent sensors. The results also open up the exploration of novel luminescent Ln-WCOFs exhibiting unique applications in sensitive detecting of harmful pollutants in aquatic environments.

Synthesis, structures and magnetic properties of two chiral mixed-valence iron(ii,iii) coordination networks

Two rare chiral mixed-valence iron(ii,iii) coordination networks have been synthesized through spontaneous asymmetrical crystallization from achiral units in the assembly process.

Highly tuneable proton-conducting coordination polymers derived from a sulfonate-based ligand

Three highly proton-conducting coordination compounds have been synthesized via the HCl steaming-assisted conversion approach by using multiple functional groups including the sulfonate group and the Cl⁻ or HPO₄²⁻ group.

Interplaying anions in a supramolecular metallohydrogel to form metal organic frameworks

A low molecular weight metallohydrogel has been selectively transformed into metal organic frameworks in the presence of different anions.

Preparation and exceptional adsorption performance of porous MgO derived from a metal–organic framework

Porous MgO-hex and MgO-dhp materials were synthesized by annealing metal–organic framework [NH₄][Mg(HCOO)₃], and exhibit excellent adsorption capacities toward Congo red.

A crystalline zinc(ii) complex showing hollow hexagonal tubular morphology evolution, selective dye absorption and unique response to UV irradiation

A protonated mononuclear complex [Zn(Hbpvp)Cl₃] (1) is assembled by solvothermal reaction of Zn(NO₃)₂·6H₂O with 3,5-bis-(2-(pyridin-4-yl)vinyl)pyridine (bpvp) in DMF/H₂O with a few drops of concentrated HCl added.

Ion-pair coordination driven stimuli-responsive one-dimensional supramolecular helicate

A new self-assembled ion-pair coordination driven one-dimensional (1D) smart supramolecular helical assembly is reported. Moreover, thermo- and chemo-responsive transformation/disassembly/reassembly of the helical superstructure was also demonstrated.

A porous copper–organic framework with intersecting channels and gas adsorption properties

Integration of [CuI2I₂] and [CuII2(COO)₄(H₂O)₂] clusters produces a porous copper–organic framework, exhibiting high H₂ uptake capacity and excellent adsorption selectivity for CO₂ over N₂ and CH₄.

Missing metal-linker connectivities in a 3-D robust sulfonate-based metal–organic framework for enhanced proton conductivity

We demonstrate the first example of proton conductivity control with the missing metal–ligand connectivities within a rare 3-D porous sulfonate-based MOF.

Metal–organic frameworks with Lewis acidity: synthesis, characterization, and catalytic applications

In this highlight, we review the recent development in the design and synthesis of metal–organic frameworks with Lewis acidity, the characterization techniques of Lewis acid sites, and their applications in heterogeneous catalysis.

The duality of UiO-67-Pt MOFs: connecting treatment conditions and encapsulated Pt species by operando XAS

XAS study of Pt-functionalized UiO-67 MOFs shows that 2 types of catalytically active sites can be formed in MOF cavities isolated Pt-complexes and Pt nanoparticles.

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.

Two luminescent Zn(ii)/Cd(ii) metal–organic frameworks as rare multifunctional sensors

Herein, two luminescent Zn(ii)/Cd(ii) metal–organic frameworks were developed as rare multifunctional sensors for the selective and sensitive detection of Fe³⁺, Al³⁺, and TNP.

Adaptability of the metal(iii,iv) 1,2,3-trioxobenzene rod secondary building unit for the production of chemically stable and catalytically active MOFs

Metal-1,2,3-trioxobenzene rod secondary building units are robust enough to adapt to cations of various charges.

Microporous rod metal–organic frameworks with diverse Zn/Cd–triazolate ribbons as secondary building units for CO2 uptake and selective adsorption of hydrocarbons

Three rod MOFs exhibiting remarkable CO₂ uptake and high CO₂ and C₂-hydrocarbons over CH₄ selectivity, as well as high isosteric heat of adsorption for C₂H₂.

A core–shell metal–organic-framework (MOF)-based smart nanocomposite for efficient NIR/H2O2-responsive photodynamic therapy against hypoxic tumor cells

In this work, core–shell MOF-based smart nanocomposite UCNPs/MB@ZIF-8@catalase has been constructed for bio-imaging and efficient NIR/H₂O₂-responsive photodynamic therapy against hypoxic tumor cells.