Metal-organic frameworks based on previously unknown Zr8/Hf8 cubic clusters

Fabrication of (4, 10) and (4, 12)-Connected Multifunctional Zirconium Metal-Organic Frameworks for the Targeted Adsorption of a Guest Molecule

Following the principle of a topology guide, a zirconium MOF (PCN-207) based on the H₄TPTA ligand (tetramethyl(4,4',4″,4‴-(pyrazine-2,3,5,6-tetrayl))tetrabenzoic acid) with C₂ symmetry and an 8-connected Zr₆(μ_3-OH)₈(OH)₈]⁸⁺ cluster with D_4h symmetry has been synthesized. PCN-206 can also be obtained by modulating the benzoic acid usage to change the flexibility of the H₄TPTA ligand. The unique positions of 8-connected Zr₆ clusters in the flu and scu networks and the flexibility of the tetratopic primary linker enable the precise insertion of fumarate (FA), 1,4-benzenedicarboxylic acid (H₂BDC), and even 2,6-naphthalenedicarboxylic acid (H₂NDC) in a one-pot reaction. Auxiliary linkers are used to generate new MOF structures or topologies or to split the pore spaces, which may significantly change the porosity and chemical and physical properties of scaffold MOFs. The results provide a successful strategy for the rational design of multicomponent Zr-MOFs. Because of differences in composition and configuration between structures, PCN-207 shows the highest separation capability of light hydrocarbons; moreover, PCN-206 exhibits the highest adsorption capacity of 2,4-D and DCF among MOFs at present.

Substrate templated synthesis of single-phase and uniform Zr-porphyrin-based metal–organic frameworks

We successfully demonstrate that the chemical bath deposition (CBD) method is a versatile method for synthesizing phase-pure and uniform MOFs by controlling their nucleation stages and pore structures.

Large-Scale Structural Refinement and Screening of Zirconium Metal-Organic Frameworks for H2S/CH4 Separation

Zirconium-based metal-organic frameworks (Zr-MOFs) with Zr₆ inner cores represent a subfamily of nanoporous materials with good physicochemical stabilities, showing significant prospect for practical applications in various fields. Although computational characterization can play an important role that is complementary to experimental efforts, the availability of chemically realistic Zr-MOF structures is one of the prerequisites to accurately evaluate their performance as well as provide valuable insights for guiding material design. In this work, periodic density functional theory (DFT) calculations combined with a molecular mechanics method were performed to optimize the crystalline structures of over 182 experimentally synthesized Zr-MOFs that contain no less than 10-coordinated Zr₆O₈ nodes, leading to a database consisting of the structures having a diversity of topologies, pore sizes, and functionalities. Apart from determination of favorable configurations of organic linkers, rational proton topologies of the 11- and 10-coordinated Zr₆O₈ nodes were also clarified. Computational screening was further conducted to examine the H₂S/CH₄ separation properties of each material in the database. Significant difference were observed by comparing the separation properties of Zr-MOFs with optimized and nonoptimized structures. Some promising candidates with high H₂S adsorption capacity and separation selectivity were identified on the basis of some evaluation metrics, and favorable organic linkers for designing new high-performance Zr-MOFs were also proposed.

Encapsulating Perovskite Quantum Dots in Iron-Based Metal-Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low-cost CH₃ NH₃ PbI₃ (MAPbI₃ ) perovskite QDs in the pores of earth-abundant Fe-porphyrin based metal organic framework (MOF) PCN-221(Fe_x ) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI₃ @PCN-221(Fe_x ) (x=0-1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO₂ reduction. Using water as an electron source, MAPbI₃ @PCN-221(Fe_0.2 ) exhibits a record-high total yield of 1559 μmol g^-1 for photocatalytic CO₂ reduction to CO (34 %) and CH₄ (66 %), 38 times higher than that of PCN-221(Fe_0.2 ) in the absence of perovskite QDs.

Hierarchical Hybrid Metal-Organic Frameworks: Tuning the Visible/Near-Infrared Optical Properties by a Combination of Porphyrin and Its Isomer Units

Hybrid metal-organic frameworks (MOFs) with core/shell-like hierarchical structure comprised of zirconium metal and porphyrin (e.g., TPP) and its isomer, N-confused porphyrin (NCP), were synthesized through a seed-mediated reaction. The hierarchical structures of hybrid MOFs were characterized by the microscopic image analyses (e.g., scanning electron microscope (SEM), energy dispersive X-ray (EDX) spectrometry, and confocal laser scanning microscope (CLSM)). Taking advantage of the intrinsic light-harvesting properties of the porphyrin dye and the N-confused isomer, changing the core/shell layer structures of hybrid MOFs allows for tuning of the visible-to-near-infrared (NIR) absorption/emission characters, excited-state energy migrations, and photosensitization capabilities. The Förster energy transfer event occurring in the bulk MOF samples by photoexcitation enabled us to control the photoinduced singlet oxygen generation through the comprehensive light-harvesting ability of these hybrid porphyrinic MOFs. Therefore, implementation of a precisely designed porphyrin "substitute" into the MOF-based materials indeed provides a new mimic of the photosynthetic pigment system and should be potentially applicable for solar-light-driven devices.

Constructing new metal-organic frameworks with complicated ligands from "One-Pot" in situ reactions

Metal-organic frameworks (MOFs) have emerged as one of the most fascinating libraries of porous materials. In spite of their myriad merits, practical application of most MOFs is restricted due to their high preparation cost because of the complicated organic ligands involved. To address this limitation, we propose to use simple and cheap organic precursors to synthesize MOFs with complicated ligands via "one-pot" in situ reactions of these precursors along with the formation of new MOFs. In this work, we have carefully screened several organic reactions, through which target ligands were generated in situ from easily available reactants during the MOF construction. With this "one-pot" approach, the fabrication of a series of novel MOFs by integrating the organic covalent bond and the coordinate bond has thus been realized through the judicious selection of organic reactions, which effectively simplifies the MOF synthesis process and thus reduces the cost.

Topology and porosity control of metal-organic frameworks through linker functionalization

Tetratopic organic linkers have been extensively used in Zr-based metal-organic frameworks (MOFs) where diverse topologies have been observed. Achieving meticulous control over the topologies to tune the pore sizes and shapes of the resulting materials, however, remains a great challenge. Herein, by introducing substituents to the backbone of tetratopic linkers to affect the linker conformation, phase-pure Zr-MOFs with different topologies and porosity were successfully obtained under the same synthetic conditions. The conversion of CO2 to valuable cyclic carbonates is a promising route for the mitigation of the greenhouse gas. Owing to the presence of substrate accessible Lewis acidic Zr(iv) sites in the 8-connected Zr6 nodes, the Zr-MOFs in this study have been investigated as heterogenous acid catalysts for CO2 cycloaddition to styrene oxide. The MOFs exhibited drastically different catalytic activities depending on their distinct pore structures. Compared to previously reported MOF materials, a superior catalytic activity was observed with the mesoporous NU-1008, giving an almost 100% conversion under mild conditions.

Light harvesting and energy transfer in a porphyrin-based metal organic framework

We present the synthesis and photophysical characterization of a water stable PCN-223(freebase) metal organic framework (MOF) constructed from meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP). The photophysical properties of the synthesized crystalline material were studied using a wide range of steady-state and time-resolved spectroscopic techniques. Quenching experiments performed on TCPP and PCN-223 demonstrated that the extent and the rate of quenching in the MOF is significantly higher than the monomeric ligand. Based on these results, we propose that upon photo-excitation, the singlet excitation energy migrates across neutral TCPP linkers until it is quenched by a N-protonated TCPP linker. The N-protonated linkers act as trap states that deactivate the excited state to the ground state. Variable temperature measurements aided in understanding the mechanism of singlet-singlet energy transfer in the PCN-223 MOF. The rate of energy transfer and the total exciton hopping distance in PCN-223 were calculated in order to quantify the energy transfer characteristics of PCN-223. Nanosecond transient absorption spectroscopy was used to study the triplet excited state photophysics in both the free ligand and PCN-223 MOF. Furthermore, femtosecond transient absorption spectroscopy was employed to get a better understanding of the photophysical processes taking place in the ligand and MOF on ultrafast timescales. Efficient energy transfer (Förster radius = 54.5 Å) accompanied with long distance exciton hopping (173 Å) was obtained for the PCN-223 MOF.

A highly augmented, (12,3)-connected Zr-MOF containing hydrated coordination sites for the catalytic transformation of gaseous CO2 to cyclic carbonates

A Zr-MOF, which contains partially hydrated, 12-connected {Zr₆} nodes and extended carboxylate ligands was synthesized, characterised and utilised in CO₂ cycloaddition catalysis.

High-throughput synthesis and characterization of nanocrystalline porphyrinic zirconium metal-organic frameworks

We describe and employ a high-throughput screening method to accelerate the synthesis and identification of pure-phase, nanocrystalline metal-organic frameworks (MOFs). We demonstrate the efficacy of this method through its application to a series of porphyrinic zirconium MOFs, resulting in the isolation of MOF-525, MOF-545, and PCN-223 on the nanoscale.

Catalysis and photocatalysis by metal organic frameworks

This review aims to provide different strategies employed to use MOFs as solid catalysts and photocatalysts in organic transformations.

More versatility than thought: large {Zr26} oxocarboxylate cluster by corner-sharing of standard octahedral subunits

The largest known zirconium cluster with an idealized formula of [Zr₂₆O₁₈(OH)₃₀(HCOO)₃₈] was obtained via solvolysis of ZrOCl₂ in DMF/HCOOH.

Carbene insertion into N–H bonds with size-selectivity induced by a microporous ruthenium–porphyrin metal–organic framework

A stable and porous porphyrinic metal–organic framework Ru-PMOF-1(Hf) has been prepared and used for N–H insertion reactions with high efficiency and selectivity.

Incorporation of an intact dimeric Zr12 oxo cluster from a molecular precursor in a new zirconium metal–organic framework

A dimeric Zr₁₂ oxo cluster was used as new molecular building block in construction of metal–organic frameworks utilizing the precursor approach.

Heterogeneous Catalysis in Zeolites, Mesoporous Silica, and Metal-Organic Frameworks

Crystalline porous materials are important in the development of catalytic systems with high scientific and industrial impact. Zeolites, ordered mesoporous silica, and metal-organic frameworks (MOFs) are three types of porous materials that can be used as heterogeneous catalysts. This review focuses on a comparison of the catalytic activities of zeolites, mesoporous silica, and MOFs. In the first part of the review, the distinctive properties of these porous materials relevant to catalysis are discussed, and the corresponding catalytic reactions are highlighted. In the second part, the catalytic behaviors of zeolites, mesoporous silica, and MOFs in four types of general organic reactions (acid, base, oxidation, and hydrogenation) are compared. The advantages and disadvantages of each porous material for catalytic reactions are summarized. Conclusions and prospects for future development of these porous materials in this field are provided in the last section. This review aims to highlight recent research advancements in zeolites, ordered mesoporous silica, and MOFs for heterogeneous catalysis, and inspire further studies in this rapidly developing field.

Controlled Release of Naringin in Metal-Organic Framework-Loaded Mineralized Collagen Coating to Simultaneously Enhance Osseointegration and Antibacterial Activity

Two important goals in orthopedic implant research are to promote osseointegration and prevent infection. However, much previous effort has been focused on the design of coatings to either enhance osseointegration while ignoring antibacterial activity or vice versa, to prevent infection while ignoring bone integration. Here, we designed a multifunctional mineralized collagen coating on titanium with the aid of metal-organic framework (MOF) nanocrystals to control the release of naringin, a Chinese herbal medicine that could promote osseointegration and prevent bacterial infection. The attachment, proliferation, osteogenic differentiation, and mineralization of mesenchymal stem cells on the coating were significantly enhanced. Meanwhile, the antibacterial abilities against Staphylococcus aureus were also promoted. Furthermore, release kinetics analysis indicated that the synergistic effect of a primary burst release stage and secondary slow release stage played a critical role in the performance and could be controlled by the relative concentrations of MOF and naringin. This work thus provides a novel strategy to engineer multifunctional orthopedic coatings that can enhance osseointegration and simultaneously inhibit microbial cell growth.

The Highly Connected MOFs Constructed from Nonanuclear and Trinuclear Lanthanide-Carboxylate Clusters: Selective Gas Adsorption and Luminescent pH Sensing

The highly odd-numbered 15-connected nonanuclear [Ln₉(μ₃-O)₂(μ₃-OH)₁₂(O₂C-)₁₂(HCO₂)₃] and 9-connected trinuclear [Ln₃(μ₃-O)(O₂C-)₆(HCO₂)₃] lanthanide-carboxylate clusters with triangular and linear carboxylate bridging ligands were synergistically combined into Ln-MOFs, [(CH₃)₂NH₂]₃{[Ln₉(μ₃-O)₂(μ₃-OH)₁₂(H₂O)₆][Ln₃(μ₃-O)(H₂O)₃](HCO₂)₃(BTB)₆}·(solvent)_x (abbreviated as JXNU-3, Ln = Gd, Tb, Er; BTB^3- = benzene-1,3,5-tris(4-benzoate)), displaying a (3,9,15)-connected topological net. The JXNU-3(Tb) exhibits highly selective CO₂ adsorption capacity over CH₄ that resulted from the high localized charge density induced by the presence of the nonanuclear and trinuclear cluster units. In addition, JXNU-3(Tb) with high chemical stability and characteristic bright green color exhibits fluorescent pH sensing, which is pertinent to the different protonation levels of the carboxylate groups of the benzene-1,3,5-tris(4-benzoate) ligand with varying pH.

Design and synthesis of coordination polymers with chelated units and their application in nanomaterials science

The advances and problems associated with the preparation, properties and structure of coordination polymers with chelated units are presented and assessed.

Coordination frameworks containing compounds as catalysts

This article describes a collection of MOF containing compounds as catalysts in a diverse range of organic transformation reactions.

Boosting selective oxidation of cyclohexane over a metal–organic framework by hydrophobicity engineering of pore walls

Hydrophobicity engineering for an iron-porphyrinic metal–organic framework has been developed to greatly improve the catalytic performance toward cyclohexane oxidation.

A gigantic polyoxozirconate with visible photoactivity

We present the synthesis and structure of a gigantic polyoxozirconate nanocluster (Zr₁₈O₂₁(μ₂-OH)₂(OOCPh)₂₈), involving 6, 7 and 8-coordinated Zr atoms. It represents the largest and the first visible-active polyoxozirconate so far. And the cluster exhibits visible light driven photocatalytic activity for H₂ production.

Efficient Visible-Light-Driven Carbon Dioxide Reduction by a Single-Atom Implanted Metal-Organic Framework

Modular optimization of metal-organic frameworks (MOFs) was realized by incorporation of coordinatively unsaturated single atoms in a MOF matrix. The newly developed MOF can selectively capture and photoreduce CO₂ with high efficiency under visible-light irradiation. Mechanistic investigation reveals that the presence of single Co atoms in the MOF can greatly boost the electron-hole separation efficiency in porphyrin units. Directional migration of photogenerated excitons from porphyrin to catalytic Co centers was witnessed, thereby achieving supply of long-lived electrons for the reduction of CO₂ molecules adsorbed on Co centers. As a direct result, porphyrin MOF comprising atomically dispersed catalytic centers exhibits significantly enhanced photocatalytic conversion of CO₂ , which is equivalent to a 3.13-fold improvement in CO evolution rate (200.6 μmol g^-1  h^-1 ) and a 5.93-fold enhancement in CH₄ generation rate (36.67 μmol g^-1  h^-1 ) compared to the parent MOF.