Association of liquid-assisted grinding with aging accelerates the inherently slow slipping-on of a dibenzo-24-crown-8 over the N-hydroxysuccinimide ester of an ammonium-containing thread

Very efficient slipping-on of the dibenzo-24-crown-8 over the NHS end of an ammonium-containing molecular axle was carried out through a solvent-less procedure.

2H NMR reveals liquid state-like dynamics of arene guests inside hexameric pyrogallol[4]arene capsules in the solid state

Guest dynamics inside pyrogallol[4]arene hexamers in the solid state are sensitive to structure external to the host.

Stoichiometry mechanosynthesis and interconversion of metal salts containing [CuCl3(H2O)]− and [Cu2Cl8]4−

The mechanochemical interconversion of two salts was achieved by the addition of an appropriate amount of one of the corresponding components (HL or CuCl₂·2H₂O), and the progress of dynamic interconversion was revealed by PXRD, fluorescence and Raman spectroscopy.

Stoichiometric control: 8- and 10-coordinate Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 complexes of the early lanthanides La-Sm

The coordination sphere of early lanthanide(iii) ions is highly versatile, exhibiting the ability to form 8-, 9-, and 10-coordinate complexes with the same ligand set. The ability to isolate 10-coordinate complexes decreases across the period, and the late lanthanides typically cannot support a coordination number higher than eight. Using two common, commercially available ligands, hfac (1,1,1,5,5,5-hexafluoroacetylacetonato-) and bpy (2,2'-bipyridine), the 8- and 10-coordinate series Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 (Ln = La-Sm) are compiled in a single investigation, demonstrating that the desired coordination number can be targeted through stoichiometry. Solvent-free syntheses of Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 complexes from Ln(hfac)3(H2O)3 precursors are investigated using a mechanochemical approach. Structural and spectroscopic properties as well as melting point trends are reported for the series.

Sonochemical fabrication of Cu(II) and Zn(II) metal-organic framework films on metal substrates

In this article, we demonstrate a rapid and facile method for in-situ growth of metal-organic framework (MOF) films on Cu or Zn metal substrates by sonochemical techniques. The substrates were first treated with a strong oxidizing agent to convert the metal to the corresponding metal hydroxide. Ultrasonic irradiation provided the energy to drive the reaction between the metal ion sources and organic ligands. Four MOF films (Cu-BTC, Cu-BDC, ZIF-8 and MOF-5) were successfully fabricated by this approach. The produced films were characterized by scanning electron microscopy and X-ray diffraction analysis. The effects of organic ligand concentration and ultrasonic irradiation time on MOF film synthesis were also systematically investigated. The rapid and facile fabrication method presented in this article could serve a new route to grow MOF films on various gas sensor surfaces. Of the MOF films, ZIF-8 film was tested as a potential methane sensor.

Solvent-Free Enzyme Activity: Quick, High-Yielding Mechanoenzymatic Hydrolysis of Cellulose into Glucose

Mechanochemistry enables enzymatic cleavage of cellulose into glucose without bulk solvents, acids, other aggressive reagents, or substrate pre-treatment. This clean mechanoenzymatic process (coined RAging) is also directly applicable to biomass, avoids many limitations associated with the use of cellulases, and produces glucose concentrations greater than three times that obtained by conventional methods.

Towards medicinal mechanochemistry: evolution of milling from pharmaceutical solid form screening to the synthesis of active pharmaceutical ingredients (APIs)

This overview highlights the emergent area of mechanochemical reactions for making active pharmaceutical ingredients (APIs), and covers the latest advances in the recently established area of mechanochemical screening and synthesis of pharmaceutical solid forms, specifically polymorphs, cocrystals, salts and salt cocrystals. We also provide an overview of the most recent developments in pharmaceutical uses of mechanochemistry, including real-time reaction monitoring, techniques for polymorph control and approaches for continuous manufacture using twin screw extrusion, and more. Most importantly, we show how the overlap of previously unrelated areas of mechanochemical screening for API solid forms, organic synthesis by milling, and mechanochemical screening for molecular recognition, enables the emergence of a new research discipline in which different aspects of pharmaceutical and medicinal chemistry are addressed through mechanochemistry rather than through conventional solution-based routes. The emergence of such medicinal mechanochemistry is likely to have a strong impact on future pharmaceutical and medicinal chemistry, as it offers not only access to materials and reactivity that are sometimes difficult or even impossible to access from solution, but can also provide a general answer to the demands of the pharmaceutical industry for cleaner, safer and efficient synthetic solutions.

Green applications of metal–organic frameworks

MOFs as green materials – a highlight of the environmentally conscious or “green” applications of MOFs.

Kitchen grinder: a tool for the synthesis of metal–organic frameworks towards size selective dye adsorption

A simple, swift mechanochemical approach for MOF synthesis using kitchen grinder has been developed for size selective dye adsorption.

Efficient and Rapid Mechanochemical Assembly of Platinum(II) Squares for Guanine Quadruplex Targeting

We present a rapid and efficient method to generate a family of platinum supramolecular square complexes, including previously inaccessible targets, through the use of ball milling mechanochemistry. This one-pot, two-step process occurs in minutes and enables the synthesis of the squares [Pt₄(en)₄(N∩N)₄][CF₃SO₃]₈ (en= ethylenediamine, N∩N = 4,4'-bipyridine derivatives) from commercially available precursor K₂PtCl₄ in good to excellent yields. In contrast, solution-based assembly requires heating the reagents for weeks and gives lower yields. Mechanistic investigations into this remarkable rate acceleration revealed that solution-based assembly (refluxing for days) results in the formation of large oligomeric side-products that are difficult to break down into the desired squares. On the other hand, ball milling in the solid state is rapid and appears to involve smaller intermediates. We examined the binding of the new supramolecular squares to guanine quadruplexes, including oncogene and telomere-associated DNA and RNA sequences. Sub-micromolar binding affinities were obtained by fluorescence displacement assays (FID) and isothermal titration calorimetry (ITC), with binding preference to telomere RNA (TERRA) sequences. ITC showed a 1:1 binding stoichiometry of the metallosquare to TERRA, while the stoichiometry was more complex for telomeric quadruplex DNA and a double-stranded DNA control.

Peptide synthesis: ball-milling, in solution, or on solid support, what is the best strategy?

While presenting particularly interesting advantages, peptide synthesis by ball-milling was never compared to the two traditional strategies, namely peptide syntheses in solution and on solid support (solid-phase peptide synthesis, SPPS). In this study, the challenging VVIA tetrapeptide was synthesized by ball-milling, in solution, and on solid support. The three strategies were then compared in terms of yield, purity, reaction time and environmental impact. The results obtained enabled to draw some strengths and weaknesses of each strategy, and to foresee what will have to be implemented to build more efficient and sustainable peptide syntheses in the near future.

Mechanically induced pyrogallol[4]arene hexamer assembly in the solid state extends the scope of molecular encapsulation

Ball milling mixtures of pyrogallol[4]arene and guests gives direct access to encapsulation complexes and can be monitored by solid-state NMR.

Pyrogallol[4]arene hexamers are hydrogen-bonded molecular capsules of exceptional kinetic stability that can entrap small molecule guests indefinitely, without exchange, at ambient temperatures. Here, we report on the use of a ball mill to induce self-assembly of the capsule components and the guests in the solid state. Stoichiometric amounts of pyrogallol[4]arene and a guest, which can be an arene, alkane, amine, or carboxylic acid, were milled at 30 Hz for fixed durations, dissolved, and characterization by NMR. Most of the resulting encapsulation complexes were kinetically stable but thermodynamically unstable in solution, and the yield of their formation correlates with the duration of the milling and is related to the structures of guest and host. This method extends the scope of molecular encapsulation, as demonstrated by the preparation of kinetically trapped encapsulation complexes of [2.2]paracyclophane, for which we could find no other method of preparation. To gain mechanistic insights into the solid-state assembly process, we characterized the milled powders using ¹³C CP-MAS NMR, we studied the effects of changing the alkane domain of the host, and we examined how dissolution conditions impact on the distribution of observed encapsulation complexes once in solution. The results support a mechanism comprising mechanically induced solid-state reorganization to produce a mixture rich in nearly or fully assembled guest-filled capsules.

Greening the Processes of Metal-Organic Framework Synthesis and their Use in Sustainable Catalysis

Given the shortage of sustainable resources and the increasingly serious environmental issues in recent decades, the demand for clean technologies and sustainable feedstocks is of great interest to researchers worldwide. With regard to the fields of energy saving and environmental remediation, the key point is the development of efficient catalysts, not only in terms of facile synthesis methods, but also the benign utilization of such catalysts. This work reviews the use of metal-organic frameworks (MOFs) and MOF-based materials in these fields. The definition of MOFs and MOF-based materials will be primarily introduced followed by a brief description of the characterization and stability of MOF-related materials under the applied conditions. The greening of MOF synthesis processes will then be discussed and catalogued by benign solvents and conditions and green precursors of MOFs. Furthermore, their suitable application in sustainable catalysis will be summarized, focusing on several typical atom-economic reactions, such as the direct introduction of H₂ or O₂ and C-C bond formation. Approaches towards reducing CO₂ emission by MOF-based catalysts will be described with special emphasis on CO₂ fixation and CO₂ reduction. In addition, driven by the explosive growth of energy consumption in the last century, much research has gone into biomass, which represents a renewable alternative to fossil fuels and a sustainable carbon feedstock for chemical production. The advanced progress of biomass-related transformations is also illustrated herein. Fundamental insights into the nature of MOF-based materials as constitutionally easily recoverable heterogeneous catalysts and as supports for various active sites is thoroughly discussed. Finally, challenges facing the development of this field and the outlook for future research are presented.

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.

Advances in Solid-State Transformations of Coordination Bonds: From the Ball Mill to the Aging Chamber

Controlling the formation of coordination bonds is pivotal to the development of a plethora of functional metal-organic materials, ranging from coordination polymers, metal-organic frameworks (MOFs) to metallodrugs. The interest in and commercialization of such materials has created a need for more efficient, environmentally-friendly routes for making coordination bonds. Solid-state coordination chemistry is a versatile greener alternative to conventional synthesis, offering quantitative yields, enhanced stoichiometric and topological selectivity, access to a wider range of precursors, as well as to molecules and materials not readily accessible in solution or solvothermally. With a focus on mechanochemical, thermochemical and “accelerated aging” approaches to coordination polymers, including pharmaceutically-relevant materials and microporous MOFs, this review highlights the recent advances in solid-state coordination chemistry and techniques for understanding the underlying reaction mechanisms.

Synthesis and characterization of nanoscale zeolitic imidazolate frameworks with ciprofloxacin and their applications as antimicrobial agents

The present study investigated antibiotic drug loading in metal–organic frameworks (MOFs).

Mechanochemically-assisted solid-state photocatalysis (MASSPC)

Simultaneous milling and visible light irradiation have been utilised to perform the photocatalytic oxidation of an alkyne in the solid state.

Biomimetic mineralization of metal–organic frameworks around polysaccharides

Biomimetic mineralization exploits natural biomineralization processes for the design and fabrication of synthetic functional materials.

Alternative synthetic approaches for metal–organic frameworks: transformation from solid matters

This review summarizes alternative approaches for MOF synthesis by using solvent-insoluble “solid matters” as cation reservoirs and/or templates.

Water-based synthesis of zeolitic imidazolate framework-8 for CO2 capture

ZIF-8 synthesized in aqueous solution has a large surface area and high CO₂ adsorption capacity.

Chemical vapour deposition of zeolitic imidazolate framework thin films

Integrating metal-organic frameworks (MOFs) in microelectronics has disruptive potential because of the unique properties of these microporous crystalline materials. Suitable film deposition methods are crucial to leverage MOFs in this field. Conventional solvent-based procedures, typically adapted from powder preparation routes, are incompatible with nanofabrication because of corrosion and contamination risks. We demonstrate a chemical vapour deposition process (MOF-CVD) that enables high-quality films of ZIF-8, a prototypical MOF material, with a uniform and controlled thickness, even on high-aspect-ratio features. Furthermore, we demonstrate how MOF-CVD enables previously inaccessible routes such as lift-off patterning and depositing MOF films on fragile features. The compatibility of MOF-CVD with existing infrastructure, both in research and production facilities, will greatly facilitate MOF integration in microelectronics. MOF-CVD is the first vapour-phase deposition method for any type of microporous crystalline network solid and marks a milestone in processing such materials.

Mechanochemical and solvent-free assembly of zirconium-based metal-organic frameworks

We develop the first mechanochemical and solvent-free routes for zirconium metal-organic frameworks, making the frameworks UiO-66 and UiO-66-NH2 accessible on the gram scale without strong acids, high temperatures or excess reactants. The frameworks form either by milling, or spontaneous self-assembly by simply exposing solid mixtures of reactants to organic vapour. The generated frameworks exhibit high porosity and catalytic activity in the hydrolysis of model nerve agents, on par with their solvothermally generated counterparts.

Vapour-induced solid-state C–H bond activation for the clean synthesis of an organopalladium biothiol sensor

Room-temperature accelerated aging in the solid state has been applied for quantitative azobenzene C–H bond activation by Pd(OAc)₂. Water-soluble dicyclopalladated methyl orange is a selective chromogenic biothiol sensor at physiologically-relevant micromolar concentrations in aqueous media.

Redox-promoted associative assembly of metal-organic materials

We develop an associative synthesis of metal-organic materials that combines solid-state metal oxidation and coordination-driven self-assembly into a one-step, waste-free transformation. The methodology hinges on the unique reactivity of ortho-quinones, which we introduce as versatile oxidants for mechanochemical synthesis. Our strategy opens a previously unexplored route to paramagnetic metal-organic materials from elementary metals.

Real-Time and In Situ Monitoring of Mechanochemical Reactions: A New Playground for All Chemists

We provide a brief overview of the first techniques for direct, real-time observation of mechanochemical reactions by milling. Whereas mechanisms and kinetics of solid-state reactions induced by temperature or pressure have been extensively investigated, transformations of materials under continuous impact in a milling assembly remain largely unexplored and based on ex situ studies. The recent introduction and development of techniques for in situ monitoring of milling reactions by synchrotron X-ray powder diffraction and Raman spectroscopy has enabled the first direct insight into milling mechanochemistry, opening a new area for studies of chemical reactivity. So far, these techniques have revealed rapid, multistep reaction mechanisms and metastable intermediates that are impossible or difficult to observe or isolate in solution and have highlighted shortcomings of ex situ mechanistic studies. These pioneering advances also highlight the low level of mechanistic understanding and future challenges in developing a clear mechanistic picture of physicochemical transformations by milling.

Quantitative in situ and real-time monitoring of mechanochemical reactions

An experimental technique for in situ and real-time monitoring of mechanochemical reactions in a shaker ball mill was recently described, which utilises highly penetrating X-ray radiation available at the ID15B beamline of the European Synchrotron Radiation Facility. Herein, we describe the first attempts to perform such reaction monitoring in a quantitative fashion, by introducing an internal X-ray diffraction standard. The use of silicon as an internal standard resolved the issue with variations of the amount of the sample in the X-ray beam due to the non-uniform distribution of the sample in the reaction jar and allowed, via Rietveld analysis, the first quantitative estimate of the amorphous phase content in a mechanochemical reaction as it is being milled. We also highlight problems associated with the non-ideal mixing of the reaction mixture.

Rapid mechanochemical synthesis of two new Cd(ii)-based metal–organic frameworks with high removal efficiency of Congo red

Two new three-dimensional porous Cd(ii)-based metal–organic frameworks, TMU-8 and TMU-9, with high performance in adsorption of Congo red.

Synthesis of metal–organic framework particles and thin films via nanoscopic metal oxide precursors

Metal–organic framework films were fabricated on versatile substrates through the nanoscale-facilitated transformation of nanoscopic metal-oxide precursors.

Mechanical properties of zeolitic metal–organic frameworks: mechanically flexible topologies and stabilization against structural collapse

We report the low elastic modulus of a zeolitic MOF, along with stabilization against structural collapse by filling with solvent.

Zn10(Im)20·4DBF: an unprecedented 10-nodal zeolitic topology with a 10-MR channel and 10 crystallographically independent Zn atoms

Zn₁₀(Im)₂₀·4DBF has an unprecedented zeolitic topology and features 10 crystallographically independent Zn atoms and an unusual 4-connected 10-nodal net.

A single precursor approach for ZIF synthesis: transformation of a new 1D [Zn(Im)(HIm)2(OAc)] structure to 3D Zn(Im)2 frameworks

We successfully use a 1-dimensional (1D) chain structure with the formula [Zn(Im)(HIm)₂(OAc)] (Im = imidazolate, HIm = imidazole, OAc = carboxylate) as a single precursor/source of a metal and ligand to directly prepare 3-dimensional (3D) [Zn(Im)₂] frameworks.

Zeolitic imidazolate frameworks: next-generation materials for energy-efficient gas separations

Industrial separation processes comprise approximately 10% of the global energy demand, driven largely by the utilization of thermal separation methods (e.g., distillation). Significant energy and cost savings can be realized using advanced separation techniques such as membranes and sorbents. One of the major barriers to acceptance of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chemically stable subclass of metal organic frameworks (MOFs). The objectives of this paper are (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient separations.