Pore‐Surface Engineering by Decorating Metal‐Oxo Nodes with Phenylsilane to Give Versatile Super‐Hydrophobic Metal–Organic Frameworks (MOFs)

Hydrophobization of metal‐organic frameworks (MOFs) is important to push forward their practical use and thus has attracted increasing interest. In contrast to the previous reports, which mainly focused on the modification of organic ligands in MOFs, herein, we reported a novel strategy to decorate the metal‐oxo nodes of MOFs with phenylsilane to afford super‐hydrophobic NH₂‐UiO‐66(Zr), which shows highly improved base resistance and holds great promise in versatile applications, such as organic/water separation, self‐cleaning, and liquid‐marble fabrication. This work demonstrates the first attempt at metal‐oxo node modification for super‐hydrophobic MOFs, advancing a new concept in the design of MOFs with controlled wettability for practical applications.     

Stereoselective Halogenation of Integral Unsaturated C‐C Bonds in Chemically and Mechanically Robust Zr and Hf MOFs

Metal–organic frameworks (MOFs) containing Zr^IV‐based secondary building units (SBUs), as in the UiO‐66 series, are receiving widespread research interest due to their enhanced chemical and mechanical stabilities. We report the synthesis and extensive characterisation, as both bulk microcrystalline and single crystal forms, of extended UiO‐66 (Zr and Hf) series MOFs containing integral unsaturated alkene, alkyne and butadiyne units, which serve as reactive sites for postsynthetic modification (PSM) by halogenation. The water stability of a Zr–stilbene MOF allows the dual insertion of both ?OH and ?Br groups in a single, aqueous bromohydrination step. Quantitative bromination of alkyne‐ and butadiyne‐containing MOFs is demonstrated to be stereoselective, as a consequence of the linker geometry when bound in the MOFs, while the inherent change in hybridisation and geometry of integral linker atoms is facilitated by the high mechanical stabilities of the MOFs, allowing bromination to be characterised in a single‐crystal to single‐crystal (SCSC) manner. The facile addition of bromine across the unsaturated C?C bonds in the MOFs in solution is extended to irreversible iodine sequestration in the vapour phase. A large‐pore interpenetrated Zr MOF demonstrates an I₂ storage capacity of 279 % w/w, through a combination of chemisorption and physisorption, which is comparable to the highest reported capacities of benchmark iodine storage materials for radioactive I₂ sequestration. We expect this facile PSM process to not only allow trapping of toxic vapours, but also modulate the mechanical properties of the MOFs.     

A Showcase of Green Chemistry: Sustainable Synthetic Approach of Zirconium-Based MOF Materials

Zirconium-based metal-organic framework materials (Zr−MOFs) have more practical usage over most conventional benchmark porous materials and even many other MOFs due to the excellent structural stability, rich coordination forms, and various active sites. However, their mass-production and application are restricted by the high-cost raw materials, complex synthesis procedures, harsh reaction conditions, and unexpected environmental impact. Based on the principles of “Green Chemistry”, considerable efforts have been done for breaking through the limitations, and significant progress has been made in the sustainable synthesis of Zr−MOFs over the past decade. In this review, the advancements of green raw materials and green synthesis methods in the synthesis of Zr−MOFs are reviewed, along with the corresponding drawbacks. The challenges and prospects are discussed and outlooked, expecting to provide guidance for the acceleration of the industrialization and commercialization of Zr−MOFs.     

Hydrophobic Metal−Organic Frameworks and Derived Composites for Microelectronics Applications

The extraordinary characteristic features of metal−organic frameworks (MOFs) make them applicable for use in a variety of fields but their conductivity in microelectronics over a wide relative humidity (RH) range has not been extensively explored. To achieve good performance, MOFs must be stable in water, i. e., under humid conditions. However, the design of ultrastable hydrophobic MOFs with high conductivity for use in microelectronics as conducting and dielectric materials remains a challenge. In this Review, we discuss applications of an emerging class of hydrophobic MOFs with respect to their use as active sensor coatings, tunable low-κ dielectrics and conductivity, which provide high-level roadmap for stimulating the next steps toward the development and implementation of hydrophobic MOFs for use in microelectronic devices. Several methodologies including the incorporation of long alkyl chain and fluorinated linkers, doping of redox-active 7,7,8,8-tetracyanoquinodimethane (TCNQ), the use of guest molecules, and conducting polymers or carbon materials in the pores or surface of MOFs have been utilized to produce hydrophobic MOFs. The contact angle of a water droplet and a coating can be used to evaluate the degree of hydrophobicity of the surface of a MOF. These unique advantages enable hydrophobic MOFs to be used as a highly versatile platform for exploring multifunctional porous materials. Classic representative examples of each category are discussed in terms of coordination structures, types of hydrophobic design, and potential microelectronic applications. Lastly, a summary and outlook as concluding remarks in this field are presented. We envision that future research in the area of hydrophobic MOFs promise to provide important breakthroughs in microelectronics applications.     

Symmetry‐Guided Synthesis of Highly Porous Metal–Organic Frameworks with Fluorite Topology

Two stable, non‐interpenetrated MOFs, PCN‐521 and PCN‐523, were synthesized by a symmetry‐guided strategy. Augmentation of the 4‐connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8‐connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN‐521 has the largest BET surface area (3411 m² g^‐1), pore size (20.5×20.5×37.4 Å) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non‐interpenetrated MOFs with high porosity.     

An In Situ One‐Pot Synthetic Approach towards Multivariate Zirconium MOFs

Chemically highly stable MOFs incorporating multiple functionalities are of great interest for applications under harsh environments. Herein, we presented a facile one‐pot synthetic strategy to incorporate multiple functionalities into stable Zr‐MOFs from mixed ligands of different geometry and connectivity. Via our strategy, tetratopic tetrakis(4‐carboxyphenyl)porphyrin (TCPP) ligands were successfully integrated into UiO‐66 while maintaining the crystal structure, morphology, and ultrahigh chemical stability of UiO‐66. The amount of incorporated TCPP is controllable. Through various combinations of BDC derivatives and TCPP, 49 MOFs with multiple functionalities were obtained. Among them, MOFs modified with FeTCPPCl were demonstrated to be catalytically active for the oxidation of ABTS. We anticipate our strategy to provide a facile route to introduce multiple functionalities into stable Zr‐MOFs for a wide variety of potential applications.     

Effective and Selective Catalysts for Cinnamaldehyde Hydrogenation: Hydrophobic Hybrids of Metal–Organic Frameworks,Metal Nanoparticles,and Micro‐ and Mesoporous Polymers

Metal–organic frameworks (MOFs) as selectivity regulators for catalytic reactions have attracted much attention, especially MOFs and metal nanoparticle (NP) shelled structures, e.g., MOFs@NPs@MOFs. Nevertheless, making hydrophilic MOF shells for gathering hydrophobic reactants is challenging. Described here is a new and viable approach employing conjugated micro‐ and mesoporous polymers with iron(III) porphyrin (FeP‐CMPs) as a new shell to fabricate MIL‐101@Pt@FeP‐CMP. It is not only hydrophobic and porous for enriching reactants, but also possesses iron sites to activate C=O bonds, thereby regulating the selectivity for cinnamyl alcohol in the hydrogenation of cinnamaldehyde. Interestingly, MIL‐101@Pt@FeP‐CMP^sponge can achieve a high turnover frequency ( 1516.1 h⁻¹), with 97.3 % selectivity for cinnamyl alcohol at 97.6 % conversion.     

Effective and Selective Catalysts for Cinnamaldehyde Hydrogenation: Hydrophobic Hybrids of Metal–Organic Frameworks,Metal Nanoparticles,and Micro‐ and Mesoporous Polymers

Metal–organic frameworks (MOFs) as selectivity regulators for catalytic reactions have attracted much attention, especially MOFs and metal nanoparticle (NP) shelled structures, e.g., MOFs@NPs@MOFs. Nevertheless, making hydrophilic MOF shells for gathering hydrophobic reactants is challenging. Described here is a new and viable approach employing conjugated micro‐ and mesoporous polymers with iron(III) porphyrin (FeP‐CMPs) as a new shell to fabricate MIL‐101@Pt@FeP‐CMP. It is not only hydrophobic and porous for enriching reactants, but also possesses iron sites to activate C=O bonds, thereby regulating the selectivity for cinnamyl alcohol in the hydrogenation of cinnamaldehyde. Interestingly, MIL‐101@Pt@FeP‐CMP^sponge can achieve a high turnover frequency ( 1516.1 h^?1), with 97.3 % selectivity for cinnamyl alcohol at 97.6 % conversion.     

Combination of Optimization and Metalated‐Ligand Exchange: An Effective Approach to Functionalize UiO‐66(Zr) MOFs for CO2 Separation

The strategy to functionalize water‐stable metal–organic frameworks (MOFs) in order to improve their CO₂ uptake capacities for efficient CO₂ separation remains limited and challenging. We herein present an effective approach to functionalize a prominent water‐stable MOF, UiO‐66(Zr), by a combination of optimization and metalated‐ligand exchange. In particular, by systematic optimization, we have successfully obtained UiO‐66(Zr) of the highest BET surface area reported so far (1730 m² g^?1). Moreover, it shows a hybrid Type I/IV N₂ isotherm at 77 K and a mesopore size of 3.9 nm for the first time. The UiO‐66 MOF underwent a metalated‐ligand‐exchange (MLE) process to yield a series of new UiO‐66‐type MOFs, among which UiO‐66‐(COONa)₂‐EX and UiO‐66‐(COOLi)₄‐EX MOFs have both enhanced CO₂ working capacity and IAST CO₂/N₂ selectivity. Our approach has thus suggested an alternative design to achieve water‐stable MOFs with high crystallinity and gas uptake for efficient CO₂ separation.     

Effect of NH2 and CF3 functionalization on the hydrogen sorption properties of MOFs

The hydrogen adsorption capacity and heat of adsorption at 77 K have been evaluated for several porous metal terephthalate MOFs (MIL-53(Fe), MIL-125(Ti) and UiO-66(Zr)), as well as in their -NH(2) and -(CF(3))(2) functionalized isoreticular structures. The capacity of hydrogen is basically related to the textural properties of the solids and not to their composition. The heats of adsorption at low coverage are on the whole close to those usually reported for MOFs (6-7 kJ mol(-1)), except for the UiO-66(Zr) and MIL-53(Fe)-(CF(3))(2) analogues, whereas the presence of Lewis acid sites and/or a confinement effect enhances significantly the strength of interaction with hydrogen.     

Study of the Cycloaddition of CO2 with Styrene Oxide Over Six-Connected spn Topology MOFs (Zr,Hf) at Room Temperature

A series of MOFs with a 6-connected spn topology were synthesized (MOF-808-(Zr, Hf), PCN-777-(Zr, Hf), MOF-818-(Zr, Hf)). Through the in situ DRIFTS of NH₃ adsorption-desorption, we found that the activated catalyst mainly contains Lewis acid sites. The effects of different organic ligands on the Lewis acid of the Zr₆ cluster were analyzed by XPS and NH₃-TPD, and the relative Lewis acidity of the same metal was obtained: PCN-777>MOF-808>MOF-818. In the Py-FTIR results, we confirmed that MOF-818 has a higher acid site density. In the activity test, MOFs with mesoporous structure showed better catalytic activity under normal temperature and pressure. Among them, MOF-818 can still maintain a high degree of crystallinity after catalysis. Finally, we use density functional theory to propose the mechanism of the cycloaddition reaction of carbon dioxide and styrene oxide. The results show that the metal is coordinated with styrene oxide and halogens attack the β carbon of the epoxide.     

Competitive Excimer Formation and Energy Transfer in Zr‐Based Heterolinker Metal–Organic Frameworks

The spectroscopy and dynamics of a series of Zr‐based MOFs in dichloromethane suspension are reported. These Zr‐NADC MOFs were constructed by using different mixtures of 2,6‐naphthalenedicarboxylate (NDC) and 4‐amino‐2,6‐naphthalenedicarboxylate (NADC) as organic linkers. The fraction of NADC relative to NDC in these heterolinker MOFs ranges from 2 to 35 %. The results indicate two competitive photoprocesses: NDC excimer formation and an energy transfer (ET) from excited NDC linkers to NADC linkers. Increasing the fraction of NADC linkers in the Zr‐NADC nanostructure decreases the mean time constant of NDC excimer formation, while the NADC emission intensity experiences a drop at the highest fraction of this linker in the MOF. The first observation is explained by an increase in the energy‐transfer probability between the two linkers, and the second by emission quenching in the NADC linkers due to ultrafast charge transfer assisted by the amino group. Femtosecond time‐resolved emission studies showed that the ET process (recorded as decaying and rising components) from excited NDC to NADC takes place in 1.2 ps. Direct excitation of the NADC linkers (at 410 nm) shows a decaying, but not rising, component of 250–480 fs, which could reflect the formation of a nonemissive charge‐separation state. The results show that by using MOFs having heterolinkers it is possible to trigger and tune excimer formation and ET processes.     

Zr(IV) and Hf(IV) based metal-organic frameworks with reo-topology

Zr and Hf based MOFs with enhanced pore accessibility for large molecules and good hydrothermal stability were obtained using a bent dithienothiophene dicarboxylate and Zr(4+) or Hf(4+) source. A modulator (benzoic acid) facilitates formation of an eight-connecting cluster leading to a new framework which adopts reo topology.     

CH(4) storage and CO(2) capture in highly porous zirconium oxide based metal-organic frameworks

A series of porous Zr oxoclusters-based MOFs was computationally explored for their gas storage/capture performances. The highly porous UiO-67(Zr) and UiO-68(Zr) solids show exceptionally high CH(4) and CO(2) adsorption capacities under operating conditions that make these thermal, water and mechanical resistant materials very promising for physisorption-based processes.     

A Computational and Experimental Approach Linking Disorder,High‐Pressure Behavior,and Mechanical Properties in UiO Frameworks

Whilst many metal–organic frameworks possess the chemical stability needed to be used as functional materials, they often lack the physical strength required for industrial applications. Herein, we have investigated the mechanical properties of two UiO‐topology Zr‐MOFs, the planar UiO‐67 ([Zr₆O₄(OH)₄(bpdc)₆], bpdc: 4,4′‐biphenyl dicarboxylate) and UiO‐abdc ([Zr₆O₄(OH)₄(abdc)₆], abdc: 4,4′‐azobenzene dicarboxylate) by single‐crystal nanoindentation, high‐pressure X‐ray diffraction, density functional theory calculations, and first‐principles molecular dynamics. On increasing pressure, both UiO‐67 and UiO‐abdc were found to be incompressible when filled with methanol molecules within a diamond anvil cell. Stabilization in both cases is attributed to dynamical linker disorder. The diazo‐linker of UiO‐abdc possesses local site disorder, which, in conjunction with its longer nature, also decreases the capacity of the framework to compress and stabilizes it against direct compression, compared to UiO‐67, characterized by a large elastic modulus. The use of non‐linear linkers in the synthesis of UiO‐MOFs therefore creates MOFs that have more rigid mechanical properties over a larger pressure range.     

A Computational and Experimental Approach Linking Disorder,High‐Pressure Behavior,and Mechanical Properties in UiO Frameworks

Whilst many metal–organic frameworks possess the chemical stability needed to be used as functional materials, they often lack the physical strength required for industrial applications. Herein, we have investigated the mechanical properties of two UiO‐topology Zr‐MOFs, the planar UiO‐67 ([Zr₆O₄(OH)₄(bpdc)₆], bpdc: 4,4′‐biphenyl dicarboxylate) and UiO‐abdc ([Zr₆O₄(OH)₄(abdc)₆], abdc: 4,4′‐azobenzene dicarboxylate) by single‐crystal nanoindentation, high‐pressure X‐ray diffraction, density functional theory calculations, and first‐principles molecular dynamics. On increasing pressure, both UiO‐67 and UiO‐abdc were found to be incompressible when filled with methanol molecules within a diamond anvil cell. Stabilization in both cases is attributed to dynamical linker disorder. The diazo‐linker of UiO‐abdc possesses local site disorder, which, in conjunction with its longer nature, also decreases the capacity of the framework to compress and stabilizes it against direct compression, compared to UiO‐67, characterized by a large elastic modulus. The use of non‐linear linkers in the synthesis of UiO‐MOFs therefore creates MOFs that have more rigid mechanical properties over a larger pressure range.     

Self‐Generation of Surface Roughness by Low‐Surface‐Energy Alkyl Chains for Highly Stable Superhydrophobic/Superoleophilic MOFs with Multiple Functionalities

We transformed the hydrophilic metal–organic framework (MOF) UiO‐67 into hydrophobic UiO‐67‐R s (R=alkyl) by introducing alkyl chains into organic linkers, which not only protected hydrophilic Zr₆O₈ clusters to make the MOF interspace superoleophilic, but also led to a rough crystal surface beneficial for superhydrophobicity. The UiO‐67‐R s displayed high acid, base, and water stability, and long alkyl chains offered better hydrophobicity. Good hydrophobicity/oleophilicity were also possible with mixed‐ligand MOFs containing metal‐binding ligands. Thus, a (super)hydrophobic MOF catalyst loaded with Pd centers efficiently catalyzed Sonogashira reactions in water at ambient temperature. Studies of the hydrophobic effects of the coordination interspace and the outer surface suggest a simple de novo strategy for the synthesis of superhydrophobic MOFs that combine surface roughness and low surface energy. Such MOFs have potential for environmentally friendly catalysis and water purification.     

Flexible Zirconium MOFs as Bromine‐Nanocontainers for Bromination Reactions under Ambient Conditions

A series of flexible MOFs (PCN‐605, PCN‐606, and PCN‐700) are synthesized and applied to reversible bromine encapsulation and release. The chemical stability of these Zr‐MOFs ensures the framework's integrity during the bromine adsorption, while the framework's flexibility allows for structural adaptation upon bromine uptake to afford stronger host–guest interactions and therefore higher bromine adsorption capacities. The flexible MOFs act as bromine‐nanocontainers which elongate the storage time of volatile halides under ambient conditions. Furthermore, the bromine pre‐adsorbed flexible MOFs can be used as generic bromine sources for bromination reactions giving improved yields and selectivities under ambient conditions when compared with liquid bromine.     

Synthesis, structure, and metalation of two new highly porous zirconium metal-organic frameworks

Three new metal-organic frameworks [MOF-525, Zr(6)O(4)(OH)(4)(TCPP-H(2))(3); MOF-535, Zr(6)O(4)(OH)(4)(XF)(3); MOF-545, Zr(6)O(8)(H(2)O)(8)(TCPP-H(2))(2), where porphyrin H(4)-TCPP-H(2) = (C(48)H(24)O(8)N(4)) and cruciform H(4)-XF = (C(42)O(8)H(22))] based on two new topologies, ftw and csq, have been synthesized and structurally characterized. MOF-525 and -535 are composed of Zr(6)O(4)(OH)(4) cuboctahedral units linked by either porphyrin (MOF-525) or cruciform (MOF-535). Another zirconium-containing unit, Zr(6)O(8)(H(2)O)(8), is linked by porphyrin to give the MOF-545 structure. The structure of MOF-525 was obtained by analysis of powder X-ray diffraction data. The structures of MOF-535 and -545 were resolved from synchrotron single-crystal data. MOF-525, -535, and -545 have Brunauer-Emmett-Teller surface areas of 2620, 1120, and 2260 m(2)/g, respectively. In addition to their large surface areas, both porphyrin-containing MOFs are exceptionally chemically stable, maintaining their structures under aqueous and organic conditions. MOF-525 and -545 were metalated with iron(III) and copper(II) to yield the metalated analogues without losing their high surface area and chemical stability.