Catalytic Synthesis of Silanols by Hydroxylation of Hydrosilanes: From Chemoselectivity to Enantioselectivity

As a crucial class of functional molecules in organosilicon chemistry, silanols are found valuable applications in the fields of modern science and will be a potentially powerful framework for biologically active compounds or functional materials. It has witnessed an increasing demand for non-natural organosilanols, as well as the progress in the synthesis of these structural features. From the classic preparative methods to the catalytic selective oxidation of hydrosilanes, electrochemical hydrolysis of hydrosilanes, and then the construction of the most challenging silicon-stereogenic silanols. This review summarized the progress in the catalyzed synthesis of silanols via hydroxylation of hydrosilanes in the last decade, with a particular emphasis on the latest elegant developments in the desymmetrization strategy for the enantioselective synthesis of silicon-stereogenic silanols from dihydrosilanes.

Recent advances in surface-mounted metal-organic framework thin film coatings for biomaterials and medical applications: a review

Coatings of metal-organic frameworks (MOFs) have potential applications in surface modification for medical implants, tissue engineering, and drug delivery systems. Therefore, developing an applicable method for surface-mounted MOF engineering to fabricate protective coating for implant tissue engineering is a crucial issue. Besides, the coating process was desgined for drug infusion and effect opposing chemical and mechanical resistance. In the present review, we discuss the techniques of MOF coatings for medical application in both in vitro and in vivo in various systems such as in situ growth of MOFs, dip coating of MOFs, spin coating of MOFs, Layer-by-layer methods, spray coating of MOFs, gas phase deposition of MOFs, electrochemical deposition of MOFs. The current study investigates the modification in the implant surface to change the properties of the alloy surface by MOF to improve properties such as reduction of the biofilm adhesion, prevention of infection, improvement of drugs and ions rate release, and corrosion resistance. MOF coatings on the surface of alloys can be considered as an opportunity or a restriction. The presence of MOF coatings in the outer layer of alloys would significantly demonstrate the biological, chemical and mechanical effects. Additionally, the impact of MOF properties and specific interactions with the surface of alloys on the anti-microbial resistance, anti-corrosion, and self-healing of MOF coatings are reported. Thus, the importance of multifunctional methods to improve the adhesion of alloy surfaces, microbial and corrosion resistance and prospects are summarized.

Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in MOF-74 Thin Films

Thin films of Co-MOF-74 and Ni-MOF-74 were synthesized on Au-coated quartz crystal microbalance substrates by a vapor-assisted conversion (VAC) method that precludes the need for activation via postsynthetic solvent exchange. All thin films were structurally characterized by powder X-ray diffraction, reflection-absorption infrared spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images reveal that the Ni-MOF-74 films exists as a dense base layer with hemispherical protrusions on the surface. In contrast, the scanning electron microscopy images of the Co-MOF-74 thin films show a rough surface with spherical deposits. The thin film morphologies were different than the powders resulting from the bulk synthesis. Gravimetric vapor-phase adsorption measurements for xylene isomers and ethylbenzene within Co-MOF-74 and Ni-MOF-74 thin films were conducted, and the results were compared with those reported for the corresponding bulk powders. Despite different morphologies, the saturation capacities of Ni-MOF-74 and Co-MOF-74 thin films were found to be nearly equivalent to those reported for the bulk powders. The results demonstrate that the VAC method can produce MOF-74 thin films that retain the intrinsic properties that are observed in bulk powders.

The Effect of Pore Sizes on D2/H2 Separation Conducted by MOF-74 Analogue

Four stable MOF-74 analogue Ni2(dobdc), Ni2(dobpdc), Ni2(olz) and Ni2(dotpdc) possess abundant open metal sites (OMSs) and honeycomb channels with pore sizes ranging from 1.0 to 2.6 nm, are used to...

Seed assisted synthesis of anionic metal organic framework membrane for selective and permeable hydrogen separation

Hydrogen selective metal organic framework (MOF) membranes with excellent performances are still in high demand. Here, we are developing an anionic MOF material of CPM-5 into a membrane for H2...

Surface-Mounted Metal-Organic Frameworks: Past, Present, and Future Perspectives

Metal-organic frameworks (MOFs) are an emerging class of porous materials composed of organic linkers and metal centers/clusters. The integration of MOFs onto the solid surface as thin films/coatings has spurred great interest, thanks to leveraging control over their morphology (such as size- and shape-regulated crystals) and orientation, flexible processability, and easy recyclability. These aspects, in synergy, promise a wide range of applications, including but not limited to gas/liquid separations, chemical sensing, and electronics. Dozens of innovative methods have been developed to manipulate MOFs on various solid substrates for academic studies and potential industrial applications. Among the developed deposition methods, the liquid-phase epitaxial layer-by-layer (LPE-LbL) method has demonstrated its merits over precise control of the thickness, roughness, homogeneity, and orientations, among others. Herein, we discuss the major developments of surface-mounted MOFs (SURMOFs) in LbL process optimization, summarizing the SURMOFs' performance in different applications, and put forward our perspective on the future of SURMOFs in terms of advances in the formulation, applications, and challenges. Finally, future prospects and challenges with respect to SURMOFs growth will be discussed, keeping the focus on their widening applications.

Anisotropy in metal–organic framework thin films

Crystallite orientation dependent properties in metal–organic framework thin films.

Defect Creation in Surface-Mounted Metal-Organic Framework Thin Films

Defect engineering is a strategy for tailoring the properties of metal-organic frameworks (MOFs). Plenty of efforts have been devoted to study the defect chemistry and structures of bulk MOFs; however, the reported example of a defect-engineered surface-mounted MOF (SURMOF) thin film is rare. In this work, defects were incorporated in SURMOF thin films by using defect-generating linkers and taking advantage of the liquid-phase stepwise epitaxial layer-by-layer growth (LBL). Two methods based on the LBL, named mixing method and alternating method, are proposed for incorporating defects in the prototypical SURMOF HKUST-1 by partially substituting the parent H₃btc (benzene-1,3,5-tricarboxylic acid) linker with a set of defect-generating linkers H₂ip (isophthalic acid), H₂OH-ip (5-hydroxyisophthalic acid), and H₂pydc (3,5-pyridinedicarboxylic acid). The crystallinity and phase purity of the obtained "defected" SURMOFs were confirmed by X-ray diffraction, infrared reflection absorption spectroscopy, and Raman spectroscopy. The incorporation of the defect-generating linkers and the types of induced defects were characterized by ultraviolet-visible spectroscopy, time-of-flight secondary ion mass spectrometry, methanol adsorption, scanning electron microscopy, and ¹H nuclear magnetic resonance spectroscopy (after digestion of the samples). These two methods provide avenues for controlling the defect formation in MOF thin films.

Spectroscopy, microscopy, diffraction and scattering of archetypal MOFs: formation, metal sites in catalysis and thin films

A comprehensive overview of characterization tools for the analysis of well-known metal–organic frameworks and physico-chemical phenomena associated to their applications.

Controlled Manipulation of Metal-Organic Framework Layers to Nanometer Precision Inside Large Mesochannels of Ordered Mesoporous Silica for Enhanced Removal of Bisphenol A from Water

Considerable attention has been paid on the design of hierarchical porous metal-organic framework (MOF) composites, which not only enhances the performance but also broadens the applications of MOFs. So far, controlled manipulation of nanometer-thick MOF layers in ordered mesochannels, while retaining their respective intrinsic properties, is still a main challenge because of the difficulty of growing MOFs in confined space. Herein, using a step-by-step coordination method, the formation of a hierarchical micro-mesoporous hybrid with a wall (channel wall and coating layer) thickness of up to 8.0 nm and open pore size down to 7.7 nm has been achieved based on large mesoporous SBA-15, and the wall thickness with nanometer precision can be controlled by adjusting the growth cycles of zeolite imidazolate framework-8 (ZIF-8) coating layers. Compared to pure ZIF-8, the obtained ZIF-8@SBA-15 composites showed more than 2-fold enhancement in adsorption capacity and approximately 20-fold improvement in the adsorption rate constant for bisphenol A in water, which could be ascribed to the synergistic effects of the high adsorption ability from ZIF-8 and the fast diffusion property from SBA-15. More importantly, the degraded ZIF-8@SBA-15 composite can be completely restored by a simple immersion into 2-methylimidazole solution. The easy restorability and good reusability further enable ZIF-8@SBA-15 as a promising adsorbent for effectively removing organic contaminants from water.

Decoding Nucleation and Growth of Zeolitic Imidazolate Framework Thin Films with Atomic Force Microscopy and Vibrational Spectroscopy

The synthesis of metal‐organic framework (MOF) thin films has garnered significant attention during the past decade. By better understanding the parameters governing the nucleation and growth of such thin films, their properties can be rationally tuned, empowering their application as (reactive) membranes. Here, a combined AFM‐vibrational spectroscopy research strategy is employed to detail the chemistries governing the nucleation and growth of zeolitic imidazolate framework (ZIF) thin films, in particular isostructural Co‐ZIF‐67 and Zn‐ZIF‐8. First, a single step direct synthesis approach is used to investigate the influence of different synthesis parameters –metal/linker ratio, temperature, and metal type– on the thin film nucleation and growth behaviour. While the metal/linker ratio has a pronounced effect on the thin film nucleation rate, the temperature mainly influences the growth kinetics of nuclei forming the thin film. In addition, the nucleation and growth of ZIF thin films is shown to be highly dependent on the electronegativity of the metal type. Thin‐film thickness control can be achieved by using a multistep synthesis strategy, implying repetitive applications of single step deposition under identical synthesis conditions, for which a growth mechanism is proposed. This study provides insight into the influence of synthesis parameters on the ZIF thin film properties, using tools at hand to rationally tune MOF thin film properties.

Fabrication of ZIF-8@SiO2 Micro/Nano Hierarchical Superhydrophobic Surface on AZ31 Magnesium Alloy with Impressive Corrosion Resistance and Abrasion Resistance

Superhydrophobic coatings are highly promising for protecting material surfaces and for wide applications. In this study, superhydrophobic composites, comprising a rhombic-dodecahedral zeolitic imidazolate framework (ZIF-8@SiO₂), have been manufactured onto AZ31 magnesium alloy via chemical etching and dip-coating methods to enhance stability and corrosion resistance. Herein, we report on a simple strategy to modify hydrophobic hexadecyltrimethoxysilan (HDTMS) on ZIF-8@SiO₂ to significantly improve the property of repelling water. We show that various liquids can be stable on its surface and maintain a contact angle higher than 150°. The morphologies and chemical composition were characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FI-IR). In addition, the anticorrosion and antiattrition properties of the film were assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization and HT, respectively. Such a coating shows promising potential as a material for large-scale fabrication.

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.

Photon Upconversion at Crystalline Organic-Organic Heterojunctions

Triplet transfer across a surface-anchored metal-organic-framework heterojunction is demonstrated by the observation of triplet-triplet annihilation photon -upconversion in a sensitizer-emitter heterostructure. Upconversion thresholds under 1 mW cm^-2 are achieved. In the broader context, the double-electron-exchange mechanism of triplet transfer indicates that the heterojunction quality is sufficient for electrons to move between layers in this solution-processed crystalline heterostructure.

Emerging applications of metal–organic frameworks

Metal–organic frameworks are highly crystalline porous materials which present emerging opportunities in biotechnology, catalysis, microelectronics and photonics.

Ionothermal synthesis, magnetic transformation and hydration–dehydration properties of Co(ii)-based coordination polymers

A series of low-coordinated coordination polymers obtained under an ionic liquid medium exhibit interesting hydration–dehydration behaviour and magnetic transformations.

Challenges and recent advances in MOF–polymer composite membranes for gas separation

This review summarizes the recent progress in the fabrication of MOF-polymer membranes including the challenges, difficulties and corresponding solutions.

Patterned growth of luminescent metal–organic framework films: a versatile electrochemically-assisted microwave deposition method

Electrochemically-assisted microwave deposition technology, a facile method for spatially locating the microcrystals of luminescent metal–organic framework (LMOF) films on a surface, was reported.

The ionothermal synthesis, structure, and magnetism-structure relationship of two biphenyl tetracarboxylic acid-based metal-organic frameworks

Two new metal-organic frameworks (1-2) were ionothermally obtained by the reaction of a biphenyltetracarboxylic sodium (Na4BPTC) ligand and M(OOCCH3)2 (M = Co(1) and Mn(2)). Crystal structure analysis reveals that 1 is a Co3Na6 unit-based three dimensional heterometallic MOF, while 2 exhibits a {Mn(COO)n} chain-based three-dimensional framework. Furthermore, the magnetic measurement shows that both of them have anti-ferromagnetic properties. A combination of Density Functional Theory (DFT) and Quantum Monte Carlo (QMC) simulation uncovers that in 2 the coupling parameters between two adjacent Mn(II) ions are J1 = -2.0 cm(-1) and J2 = -1.6 cm(-1), and the magnetism mainly originates from the propagation of Mn(II) ions by the super-exchange of carboxylates. Interestingly, the superexchange modes of J1 and J2 are different. Two spin nets of -/+/- dominate in the coupling for J1, while for J2 there are two spin nets of -/+/- and one spin net of +/-/+.

Bias-Switchable Permselectivity and Redox Catalytic Activity of a Ferrocene-Functionalized, Thin-Film Metal-Organic Framework Compound

The installation of ferrocene molecules within the wide-channel metal-organic framework (MOF) compound, NU-1000, and subsequent configuration of the modified MOF as thin-film coatings on electrodes renders the MOF electroactive in the vicinity of the ferrocenium/ferrocene (Fc(+)/Fc) redox potential due to redox hopping between anchored Fc(+/0) species. The observation of effective site-to-site redox hopping points to the potential usefulness of the installed species as a redox shuttle in photoelectrochemical or electrocatalytic systems. At low supporting electrolyte concentration, we observe bias-tunable ionic permselectivity; films are blocking toward solution cations when the MOF is in the ferrocenium form but permeable when in the ferrocene form. Additionally, with ferrocene-functionalized films, we observe that the MOF's pyrene-based linkers, which are otherwise reversibly electroactive, are now redox-silent. Linker electroactivity is fully recovered, however, when the electrolyte concentration is increased 10-fold, that is, to a concentration similar to or exceeding that of an anchored shuttle molecule. The findings have clear implications for the design and use of MOF-based sensors, electrocatalysts, and photoelectrochemical devices.

Positioning of the HKUST-1 metal–organic framework (Cu3(BTC)2) through conversion from insoluble Cu-based precursors

A Cu-based metal–organic framework (HKUST-1) was synthesized from insoluble precursors and positioned using sol–gel based coatings.

Metal–organic framework materials for light-harvesting and energy transfer

This contribution highlights recent work on the photon collection and energy transport behavior of metal–organic frameworks for excitonic solar cells.

Post-assembly transformations of porphyrin-containing metal–organic framework (MOF) films fabricated via automated layer-by-layer coordination

Solvent-assisted linker exchange and post-assembly linker metalation converts existing metal–organic framework (MOF) thin films into new or modified ones.