Search

Achieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy‐efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein, we show an example that tailoring the local environment of cobalt sites in a robust metal–organic framework through substituting the bridging atom from −Cl to −OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low‐temperature CO oxidation performance was achieved with T25(Temperature for 25 % conversion)=35 °C and T100 (Temperature for 100 % conversion)=150 °C, which stands out from existing MOF‐based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction. [ABSTRACT FROM AUTHOR]

Many studies in metal‐organic frameworks (MOFs) aiming for high photocatalytic activity resort to self‐assembling both energy donor and acceptor building units in skeleton to achieve effective energy transfer, which, however, usually needs tedious synthetic procedure and design of a new MOF. In this work, we demonstrated that building a Förster resonance energy transfer (FRET) pathway can be realized through suitable molecular doping in a given MOF structure without altering the original porous structure, presenting an alternative strategy to design efficient photocatalysts for CO2 reduction. In situ electron spin resonance, ultrafast transient absorption spectroscopy, and computational studies reveal that the FRET‐induced excitation has dramatically altered the exciton transfer pathway in structure and facilitated electron‐hole separation. As a result, the molecular doped MOFs synthesized through one‐pot reaction show outstanding selectivity (96%) and activity (1314 μmol·g−1·h−1) for CO production versus almost no activity for the pristine MOFs, and this result stands out from existing competitors. Furthermore, the reaction mechanism was proposed and the intermediate signals were detected by in situ diffuse reflectance infrared Fourier transform spectroscopies. This study presents a clear picture of building FRET process in MOFs through molecular doping and provides a new design strategy for MOF‐based photocatalysts. [ABSTRACT FROM AUTHOR]

Embedding plasmonic metals in metal–organic frameworks (MOFs) can build an advanced visible‐light photocatalyst architecture utilizing the localized surface plasmon resonance (LSPR) effect, while the practical performances have been restricted by the sluggish charge transfer at metal–MOF interface and through the secondary building units (SBUs) of the adopted carboxylate MOFs currently. Herein, a pyrazolate Ni‐MOF (PFC‐9) featured with an 1D SBU chain is selected to be the host catalyst to immobilize Au nanoparticles as a novel and optimized construction for LSPR photocatalysis. Compared with the common 3D‐connected SBUs of carboxyl‐ZrOx and pyrazole‐NiOx configurations in the reference MOFs, the 1D (−Ni−NPz−NPz−)∞ chain in PFC‐9 creates abundant Au/MOF contacts, a short and low‐resistant pathway for Au‐to‐Ni2+ transport of hot electrons, and enables fluent electron utilization at the continuous active Ni sites. Consequently, the Au/PFC‐9 photocatalyst achieves the optimum activity for visible‐light‐driven H2 production. This work shows an example to promote the LSPR‐sensitized photocatalysis taking the advantage of MOFs' structural tunability, providing significant guidance for the rational design of highly efficient photocatalysts. [ABSTRACT FROM AUTHOR]

It is still a great challenge to achieve high selectivity of CH4 in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials of possible products and the sluggish kinetics for CO2 activation. Stabilizing key reaction intermediates by single type of active sites supported on porous conductive material is crucial to achieve high selectivity for single product such as CH4. Here, Cu2O(111) quantum dots with an average size of 3.5 nm are in situ synthesized on a porous conductive copper‐based metal–organic framework (CuHHTP), exhibiting high selectivity of 73 % towards CH4 with partial current density of 10.8 mA cm−2 at −1.4 V vs. RHE (reversible hydrogen electrode) in CO2RR. Operando infrared spectroscopy and DFT calculations reveal that the key intermediates (such as *CH2O and *OCH3) involved in the pathway of CH4 formation are stabilized by the single active Cu2O(111) and hydrogen bonding, thus generating CH4 instead of CO. [ABSTRACT FROM AUTHOR]

Titanium (Ti)‐based metal–organic frameworks (MOFs) have attracted intensive attention due to the low toxicity, high earth's crust abundance, and unique photocatalytic properties of Ti elements. Great efforts have been devoted to the synthesis of novel architectures and their potential applications involving photocatalysis. However, Ti‐MOFs are still very scarce owing to their challenges in controlling the Ti chemistry in the reaction system. Until now, some significant results have been achieved, which may shed new insight into the future investigation of Ti‐MOFs. Herein, some representative researches in Ti‐MOFs are summarized and reviewed from the following four aspects: first, various synthetic strategies for preparing Ti‐MOFs are introduced; second, diverse structures containing multi‐connected ligands are presented in detail; third, the potential photocatalytic applications of Ti‐based MOFs involving H2 production, CO2 reduction, H2O2 production, N2 fixation, remediation of organic and inorganic pollutants, as well as organic transformation reaction and photocatalytic sensors are discussed; finally, perspectives on current challenges and emerging opportunities in this research field are discussed. Through summarizing this specific type of MOF, this review is expected to stimulate researchers' interest for in‐depth investigation of novel structures synthesis, as well as new applications and concepts in these intriguing fields. [ABSTRACT FROM AUTHOR]

A facile method, post-synthetic exchange of modulators (PSEm), has been demonstrated here to prepare chiral metal–organic frameworks for enantioseparation. Based on this method, three chiral porous Zr-based metal–organic frameworks have been prepared through exchanging the coordinated modulators on metal clusters of MOFs with commercially available chiral carboxylic acid molecules. In addition, the obtained materials show enantioselectivity toward three different enantiomers, which presents a proof of concept for the design of MOF materials for enantioseparation by an easy and low-cost method. [ABSTRACT FROM AUTHOR]

Although many ionic metal–organic frameworks (MOFs) have been reported, little is known about how the charge of the skeleton affects the properties of the MOF materials. Herein we report how the chemical stability of MOFs can be substantially improved through embedding electrostatic interactions in structure. A MOF with a cationic skeleton is impervious to extremely acidic, oxidative, reductive, and high ionic strength conditions, such as 12 m HCl (301 days), aqua regia (86 days), H2O2 (30 days), and seawater (30 days), which is unprecedented for MOFs. DFT calculations suggested that steric hinderance and the repulsive interaction of the cationic framework toward positively charged species in microenvironments protects the vulnerable bonds in the structure. Diverse functionalities can be bestowed by substituting the counterions of the charged framework with identically charged functional species, which broadens the horizon in the design of MOFs adaptable to a demanding environment with specific functionalities. [ABSTRACT FROM AUTHOR]

Abstract: The low structural stability of hydrogen‐bonded organic frameworks (HOFs) is a thorny issue retarding the development of HOFs. A rational design approach is now proposed for construction of a stable HOF. The resultant HOF (PFC‐1) exhibits high surface area of 2122 m2 g−1 and excellent chemical stability (intact in concentrated HCl for at least 117 days). A new method of acid‐assisted crystalline redemption is used to readily cure the thermal damage to PFC‐1. With periodic integration of photoactive pyrene in the robust framework, PFC‐1 can efficiently encapsulate Doxorubicin (Doxo) for synergistic chemo‐photodynamic therapy, showing comparable therapeutic efficacy with the commercial Doxo yet considerably lower cytotoxicity. This work demonstrates the notorious stability issue of HOFs can be properly addressed through rational design, paving a way to develop robust HOFs and offering promising application perspectives. [ABSTRACT FROM AUTHOR]

Gaining control over the assembly of mesoporous Zr-based metal-organic frameworks (MOFs) with modifiable metal nodes remains a challenge. The the topology is intriguing, particularly if considering postsynthetic modification, as it presents large sodalite-like cages surrounded by 12 interconnected 1D channels that allow for efficient diffusion of guest molecules throughout the structure. Herein, we demonstrate the first Zr MOF with the topology, NU-1200, which was synthesized by controlling the geometry of the organic building unit. In addition, by using NU-1200 as a platform, we perform solvent-assisted metal incorporation to form single-site metalated nodes, a process that is characterized by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

Two metal-organic frameworks [PCN-426(Ni) and PCN-427(Cu)] have been designed and synthesized to investigate the structure predictability using a SBB (supermolecular building blocks) approach. Tetratopic ligands featuring 120° angular carboxylate moieties were coordinated with a [Ni3(μ3-O)] cluster and a [Cu2O2] unit, respectively. As topologically predicted, 4-connected networks with square coordination adopted the nbo net for the Ni-MOF and ssb net for the Cu-MOF. PCN-426(Ni) was augmented with 12-connected octahedral SBBs, while PCN-427(Cu) was constructed with tetragonal open channels. After a CO2 supercritical drying procedure, the PCN-426(Ni) possessed a Brunauer-Emmett-Teller (BET) surface area as high as 3935 m2 g−1 and impressively high N2 uptake of 1500 cm3 g−1. This work demonstrates the generalization of the SBB strategy, finding an alternative to inconvenient synthetic processes to achieve the desired structural features. [ABSTRACT FROM AUTHOR]

Cooperative cluster metalation and ligand migration were performed on a Zr-MOF, leading to the isolation of unique bimetallic MOFs based on decanuclear Zr6M4 (M=Ni, Co) clusters. The M2+ reacts with the μ3-OH and terminal H2O ligands on an 8-connected [Zr6O4(OH)8(H2O)4] cluster to form a bimetallic [Zr6M4O8(OH)8(H2O)8] cluster. Along with the metalation of Zr6 cluster, ligand migration is observed in which a Zr-carboxylate bond dissociates to form a M- carboxylate bond. Single-crystal to single-crystal transformation is realized so that snapshots for cooperative cluster metalation and ligand migration processes are captured by successive single-crystal X-ray structures. In3+ was metalated into the same Zr-MOF which showed excellent catalytic activity in the acetaldehyde cyclotrimerization reaction. This work not only provides a powerful tool to functionalize Zr- MOFs with other metals, but also structurally elucidates the formation mechanism of the resulting heterometallic MOFs. [ABSTRACT FROM AUTHOR]

Through topological rationalization, a zeotype mesoporous Zr-containing metal-organic framework (MOF), namely PCN-777, has been designed and synthesized. PCN-777 exhibits the largest cage size of 3.8 nm and the highest pore volume of 2.8 cm3 g−1 among reported Zr-MOFs. Moreover, PCN-777 shows excellent stability in aqueous environments, which makes it an ideal candidate as a support to incorporate different functional moieties. Through facile internal surface modification, the interaction between PCN-777 and different guests can be varied to realize efficient immobilization. [ABSTRACT FROM AUTHOR]

A 3D Magnesium MOF PCN-72 has been synthesized from the solvothermal reaction of Mg(NO3)2 and a linear ligand. This MOF has a unique structure with 1-dimensional (1D) channel as well as infinite metal chains, which resembles the topology of MIL-53. It is thermally and moisture stable. In situ powder X-ray diffraction studies reveal its interesting phase transitions under temperature change. Calculation shows that each phase of PCN-72 exhibits unique and unusual thermal expansion properties. After removing coordinated solvent at Mg chains, PCN-72 can selectively adsorb CO2 over N2. [ABSTRACT FROM AUTHOR]

Four isostructural metal-organic frameworks (MOFs) with various functionalized pore surfaces were synthesized from a series of diisophthalate ligands. These MOFs exhibit a new network topology of {4.64.8}2{42.64}{64.82}2{66}. Hydrogen uptake as high as 2.67 wt % at 77 K/1 bar and CO2 uptake of 15.4 wt % at 297 K/1 bar have been observed for PCN-308, which contains CF3 groups. The isostructural series of MOFs also showed reasonable adsorption selectivity of CO2 over CH4 and N2. [ABSTRACT FROM AUTHOR]

Two anionic metal-organic frameworks were successfully prepared based on pre-designed flexible multicarboxylate ligands and indium cations. Owing to the flexibility of the bridging organic linkers, which could not themselves sustain the frameworks, both of the frameworks showed thermal instability and shrinkage after removal of guest solvent molecules. Inspired by bamboo, we used a guest-dependent approach to tune the permanent porosity of the MOFs. In this approach, several tetraalkyammonium cations of different sizes were introduced into the channels by cation exchange to act as partitions and to support the main frameworks. This approach significantly enhanced the stability of the framework and its permanent porosity. Moreover, the gas-adsorption properties (such as gate sorption, hysteresis, and selectivity) of the MOFs were also modulated by the judicious choice of guest cations. [ABSTRACT FROM AUTHOR]

An interesting coordination complex based on a designed X ligand has been prepared. It displays a novel 4-connected uninodal net with point symbol (42·63·8) and vertex symbol [4.6.4.6.6.1012] which has never been observed in metal−organic frameworks/coordination polymers. Meanwhile, the compound displays intriguing structural features of interpenetration and self-catenation, as well as nonlinear optical properties. An interesting coordination complex based on a designed X ligand has been prepared. It displays a novel 4-connected uninodal net with point symbol (42·63·8) and vertex symbol [4.6.4.6.6.1012] which has never been observed in metal−organic frameworks/coordination polymers. Meanwhile, the compound displays intriguing structural features of interpenetration and self-catenation, as well as nonlinear optical properties. [ABSTRACT FROM AUTHOR]

The front cover picture shows the structure of the zirconium‐based metal–organic framework NU‐1200 and the principles we use to develop new materials. In essence, we use design concepts to envision new crystalline porous materials followed by synthetic organic and inorganic chemistry to construct new architectures and modify the structures to expose new properties. These strategies are interwoven and work together to give us the tools to create functional porous materials. Details are discussed in the Communication by J. T. Hupp, O. K. Farha et al. on on p. 4349 ff. For more on the story behind the cover research, see the Cover Profile. [ABSTRACT FROM AUTHOR]

Newporous metal–organic framework (MOF) films based onthe flexible ligand 1,3,5-tris[4-(carboxyphenyl)oxamethyl]-2,4,6-trimethylbenzene(H3TBTC) were fabricated on α-Al2O3substrates under solvent thermal conditions. The factorsaffecting the fabrication of films, such as the temperature of pre-activationand the dosage of the reagents, were investigated. Tuning the subtlefactors on film fabrications, a series of MOF thin films with differentmorphologies and grain sizes were prepared. The morphology and grainsize of the films are monitored by scanning electron microscopy (SEM).X-ray diffraction (XRD) and attenuated total reflection infrared (ATR–IR)were also used to characterize the MOF films. The results indicatethat the temperature of pre-activation and the dosage of the reagentsare the key parameters during the process of film formation. The propertiesof the films, especially the sensing and sorption behavior, have beenstudied by an optical digital cameral and ultraviolet–visible(UV–vis) spectra. The evidence shows that the films are sensitiveto small organic molecules, such as methanol and pyridine. Meanwhile,the films can adsorb small dye molecules. Thus, the films may havepotential applications in either organic vapor sensing or storageof small dye molecules. [ABSTRACT FROM AUTHOR]

To explore materials stable in alkaline solution, a linear ligands 1,4-benzenedi(4′-pyrazolyl), in which the pyrazolate group was considered as a soft Lewis base, was used to reacted with two relative soft Lewis acid Ni(II) and Zn(II) metal ions, to constructed stable MOFs structure. Since the metal pyrazolate clusters resemble with metal carboxylate clusters performing the same connection mode during self-assembly, the obtained materials PFC-6 and PFC-7 exhibit same topologies with classic carboxylate-based MOFs UiO-66 and MIL-53, respectively. Due to the strong coordination bond between soft Lewis base and soft Lewis acid, PFC-6 and PFC-7 exhibit high porosity and excellent stability from pH = 2 to pH = 13. Inspired by these features, PFC-6 was used as a drug carrier and the DCF drug uptake/release behavior were investigated. This work presented here demonstrates that the pyrazolate-based ligands are capable of constructing MOFs structure possessing same topologies with carboxylate ligands but high stability in alkaline solution. [ABSTRACT FROM AUTHOR]

Abstract: Three new complexes Ln(BDC)1.5(DEF) [Ln=La(1), Ce(2), Nd(3); H2BDC=1,4-benzenedicarboxylic acid; DEF= N,N-diethylformamide] have been solvothermally synthesized and characterized by single-crystal X-ray diffraction. Complexes 1–3 are isostructural and crystallize in triclinic space group . They display three-dimensional frameworks and 18.7986Å×11.3230Å rhombic channels along the a axis without interpenetration. Two eight-coordinated metal centers are connected with two dimonodentate BDC groups and two chelating/bridging bidentate BDC groups to give a paddle-wheel building block. The building blocks are connected through two carboxyl groups to lead to a one-dimensional infinite inorganic chain (–M–O–C–O–M–) along the [100] direction. Thermogravimetric analyses (TGA) and X-ray powder diffraction (XPRD) were determined for the three complexes. An observed intense blue luminescence with an emission band peaking at 372nm for them may result from ligand-to-metal charge transfer (LMCT). Variable-temperature magnetic susceptibility of 2 and 3 was investigated and found deviated from the Curie–Weiss law. [Copyright &y& Elsevier]

Two isostructural Zirconium MOFs, PFC-14 and PFC-15, based on linear ligand bearing different alkyl chains on backbones, have been synthesized under solvothermal reaction conditions. These two MOFs have the same structures with UiO-66 series but display two-fold interpenetration in structure. In situ powder X-ray diffraction during the gas loading process demonstrates that the interpenetration and the alkyl side chains on linkers, reduces the surface area though, creates adsorption sites to accommodate CO 2 and CH 4 molecules as indicated by in situ XRD studies. The work presented here provides insight on rational design of MOFs for gas adsorption and separation. Unlabelled Image • Two Zirconium MOFs, PFC-14 and PFC-15, based on linear ligand bearing different alkyl chains, have been synthesized. • These two MOFs have the same structures with UiO-66 series but display two-fold interpenetration in structure. • In situ powder X-ray diffractions during the gas loading process were conducted and analyzed by Differential Electron Density. • It shows that the interpenetration and alkyl chains on linkers creates adsorption sites to accommodate CO 2 and CH 4 molecules. [ABSTRACT FROM AUTHOR]