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Flexible metal–organic frameworks (MOFs) have been attracting increasing attention in stimuli-responsive applications. However, the effects of the MOF's structural transition on catalysis have been largely unexplored. Herein, the dynamic behaviors and catalytic ability of a flexible bimetallic MOF (i.e., MIL-88B(Fe/Co)) were systematically investigated through density functional theory calculations, which suggested rotary metal nodes and twisted ligands upon lattice contraction, subsequently leading to variable performances in the oxygen evolution reaction as confirmed by the differences in the free energy diagrams. To correlate the catalytic performance with the structural dynamics of the MOFs, partial pair distribution function analysis was carried out, which demonstrated that the short-range order of MIL-88B(Fe/Co) is unaffected by the lattice expansion/contraction, suggesting the intact bond connectivity during the structural transition. The bonding nature of the bimetallic MOF was further investigated through electron localization function analysis, which revealed that structural modulation poses negligible impacts on the bonding interactions in the metal nodes while the contracted structures can cause a closely packed framework. The dependence of the catalytic performance on the dynamic structures demonstrated in this work suggests that the structural transition of the flexible MOFs can be exploited to alter the energy barriers of the elementary steps during the catalysis processes, offering potential avenues to achieving better control over the catalytic pathways for enhanced efficiency. [ABSTRACT FROM AUTHOR]

The acylamide functionalized tetra-carboxylic acid (H4CDA) has been successfully employed for the formation of two robust 3D-MOFs, Cd-CDA-MOF and Cu-CDA-MOF, having open metal sites with two distinct and diverse network topologies namely diamondoid and PCU. The Cd-CDA-MOF is shown to act as an efficient heterogeneous catalyst for the Knoevenagel condensation reaction under mild and ambient conditions. The Cu-CDA-MOF demonstrates excellent catalytic activity for the Chan–Lam coupling reaction with a considerably high turnover number. The heterogeneous catalytic activity of the MOFs can be attributed to the coordinatively unsaturated open metal sites of the activated frameworks. The MOFs are found to be recyclable with almost uniform catalytic activity. [ABSTRACT FROM AUTHOR]

The template-directed strategy is a facile and universal method to synthesize novel and useful functional materials that are difficult to achieve by traditional methods. Herein, a ternary hybrid Cu2O/Cu/Au with a hollow structure is synthesized via a two-step template-directed strategy. Hollow Cu-MOF-74 is selected as a self-sacrificial template and calcined under an Ar atmosphere to obtain hollow Cu2O/Cu with the preservation of the original hollow structure and rod-like shape. Then, hollow Cu2O/Cu acts as a self-sacrificial template as well as a reducing agent. The metal precursors are adsorbed on the surface of Cu2O/Cu and in situ reduced to Au nanoparticles, decorating the surface uniformly and forming the hollow ternary hybrid Cu2O/Cu/Au. More importantly, hollow Cu2O/Cu/Au is equipped with enhanced electrochemical catalytic activity toward the reduction of H2O2, which is ascribed to the introduction of Au nanoparticles facilitating electron transfer in the catalytic reaction, and it can be used as a candidate for an H2O2 sensor with high sensitivity, wide detection range and low limit of detection. Selecting suitable templates provides a new opportunity for constructing hybrids with novel structures. [ABSTRACT FROM AUTHOR]

Five novel metal–organic frameworks (MOFs) with the formula [MII(dcpbpy)(sol)x]n (MII = CoII, sol = H2O, x = 1, 1; MII = NiII, sol = H2O, x = 1, 2; MII = MnII, sol = DMAc, x = 1, 3; MII = MnII, sol = DMF, x = 1, 4; MII = MnII, sol = H2O, x = 2, 5; dcpbpy = 4-(2,4-dicarboxylphenyl)-4,2′:6′,4′′-terpyridine) having various dimensions were prepared with different solvents and transition-metal ions (CoII, NiII and MnII). Single-crystal X-ray diffraction showed that 1–5 resulted in the grid layer stacked 3D (1 and 2), 2D (3 and 4) and 1D (5) frame structures due to their different coordination modes. Electrochemical analyses showed that 1–5 displayed efficient catalytic activity towards oxygen evolution reactions (OERs) under alkaline conditions. Besides, 1–2 with the stacked 3D framework could present a large interaction and result in a low overpotential of their OER behaviour, compared to the 2D (3 and 4) and 1D (5) frameworks. MOF 2 with a 3D frame structure and NiII as the active central ion gave the lowest required overpotential (130 mV) to generate a current density of 1 mA cm−2. [ABSTRACT FROM AUTHOR]

For electrochemical energy conversion, highly efficient and stable electrocatalysts are required, which are principally designed and synthesized by virtue of structural regulation. Two-dimensional cluster-based metal–organic layers (CMOLs) would have good performance in oxygen evolution reaction (OER) because of their stable and layered structure. Here, we first report the synthesis of CoNi bimetal two-dimensional CMOLs directly grown on Ni foam, which show excellent catalytic activity for the OER under alkaline conditions. Co0.6Ni0.4-CMOLs exhibited the best OER performance, compared with Co-CMOLs and Ni-CMOLs. The findings are expected to help understand the fundamental concept of enhanced electrochemical activity based on pristine metal–organic frameworks with high stability. [ABSTRACT FROM AUTHOR]

MOF-74-type frameworks are considered one of the most promising metal–organic frameworks owing to their remarkable structural features and properties such as a high density of open metal sites, hexagonal channels along the c-axis, and high porosity. Diverse strategies have been adopted to prepare bimetallic MOF-74 frameworks, in the pursuit of synergistic effects and enhanced properties originating from different metal sites that serve as Lewis acidic sites. Moreover, extended versions of the MOF-74-type structure have been demonstrated in terms of ligand extension, featuring enhanced pore size and surface area. The extended variants of MOF-74 are beneficial for the incorporation of additional functional groups due to the relatively larger pore size. Pre- or post-synthetic modification approaches have been applied to introduce functionalities into the framework, resulting in desirable and superior properties such as chemical stability, binding affinity, and catalytic activity. This review addresses the significant progress made in the development of MOF-74-type frameworks with respect to synthetic strategies and modification approaches. [ABSTRACT FROM AUTHOR]

Two new three-dimensional (3D) metal–organic frameworks (MOFs), namely {[Cu2(L)(4,4′-bipy)(OH)]·H2O}n (1) and {[Mn3(L)2(4,4′-bipy)(DMA)2]·H2O}n (2), were constructed by a newly synthesized thioether carboxylic acid ligand 5-((formic acid-3-sulfur)methyl)isophthalic acid (H3L) and 4,4′-bipyridine (4,4′-bipy). Thioether bonds in H3L can rotate freely in space, which are conducive in constructing MOFs with rich and stable structures. Simultaneously, the uncoordinated sulfur atoms affect the polarity of the framework and play an important role in adsorption. Gas adsorption results indicated that 1 can selectively adsorb CO2 from the mixture of CH4/CO2. Moreover, due to the high catalytic activity of [Cu4(COO)6N4O2] clusters, 1 is also an excellent recyclable catalyst that can chemically fix CO2 into cyclic carbonate under mild solvent-free conditions. Therefore, 1 may be explored as a dual-functional material for industrial adsorption and catalysis. [ABSTRACT FROM AUTHOR]

By utilizing a flexible fluorinated bis(triazole) ligand 1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene (Fbtx), a thermally and chemically stable cobalt(II)-containing tungstovanadate-based metal–organic framework (MOF) {[Co3(Fbtx)5(V2W18O62)(H2O)2]·26H2O}n (denoted as CZU-5) was synthesized and structurally characterized. The X-ray structural analysis revealed that CZU-5 features a three-dimensional (3-D) self-penetrated α-polonium cubic structure, which results from a 3-D 4-fold interpenetrated diamondoid [Co(Fbtx)]n network connected by the Wells–Dawson-type tungstovanadate clusters. Unexpectedly, the introduction of vanadium atoms as heteroatoms into the Dawson-type anion in polyoxometalate (POM)-based coordination polymers has not been reported to date. For the first time, the POM-based material was demonstrated to be an effective catalyst for the solvent-free ring-opening polymerization of ε-caprolactone. Moreover, the CZU-5 catalyst could be recycled up to five times with the retention of both catalytic activity and crystal structure. [ABSTRACT FROM AUTHOR]

Flower-like mesoporous sulfated zirconia nanosheets (SZNs) were developed by thermal decomposition of in situ sulfated Zr-MOFs for the first time. The sulfated Zr-MOFs act as both a morphological template and zirconium and sulfate sources. The amounts of SO42− in the synthesis system of UiO-66 greatly affected the morphology of sulfated Zr-MOFs via a coordination modulation method. The flower-like sulfated Zr-MOF nanosheets were obtained as the S/Zr ratio increased to 0.5. The calcination temperature has a great influence on the structural properties and catalytic performances of sulfated zirconia nanosheets other than morphology. Sulfated zirconia nanosheets (SZN-500) obtained by calcination at 500 °C had a large surface area (186.1 m2 g−1) and strong bonding between sulfate and zirconia atoms and exhibited a good catalytic activity and reusability for the transesterification of tributyrin with methanol. This viable synthetic strategy can offer an alternative way to prepare functionalized metallic oxides with a specific morphology. [ABSTRACT FROM AUTHOR]

The kinetically sluggish electrochemical water splitting reaction still faces great challenges, and the rational design of excellent electrocatalysts is the key to solving the problem. Herein, an etching and pyrolysis strategy is employed to dope Ru into highly hollow nanocaged RuCo@C heterostructured catalysts using the metal–organic framework ZIF-67 as a template by adjusting the annealing temperature, which not only enhances the activity but also reduces the cost. Property studies show that the optimal heterostructured catalyst RuCo@C-350 presents outstanding electrocatalytic activities with low overpotentials to drive 10 mA cm−2 for the hydrogen evolution reaction (HER, 91 mV) and oxygen evolution reaction (OER, 230 mV) under alkaline conditions. Moreover, RuCo@C-350 demonstrates remarkable catalytic behavior for overall water splitting in a two-electrode system with 1.56 V to drive a 10 mA cm−2 current density in an alkaline electrolyte. The derived highly hollow heterostructure that exposes numerous active centers and accelerates the mass transportation and the strong synergistic coupling effect between the integrated components together improve the catalytic activity and stability of the composite catalyst. This work promotes an in-depth understanding of the rational construction of MOF template-induced bifunctional Ru-based electrocatalysts. [ABSTRACT FROM AUTHOR]