Mechanochemistry provides a rapid, efficient route to metal−organic framework Zn-MOF-74 directly from a metal oxide and without bulk solvent. In situ synchrotron X-ray diffraction monitoring of the reaction course reveals two new phases and an unusual stepwise process in which a close-packed intermediate reacts to form the open framework. The reaction can be performed on a gram scale to yield a highly porous material after activation.M etal−organic frameworks (MOFs) 1 are advanced materials with applications ranging from storage and separation of fuel gases, 2 CO 2 sequestration, 3 and degradation of nerve agents 4 to fuel cells, 5 catalysis, 6 drug delivery 7 and light harvesting. 8 Commercialization of MOFs has highlighted unique synthetic challenges, 9 often involving solvothermal conditions and soluble reagents which, while common in a laboratory, are intractable in large-scale manufacturing due to issues of cost, toxicity, and explosive (nitrates) or corrosive (chlorides) nature. 9,10 It was recently demonstrated that liquid-catalyzed mechanochemistry 11 (e.g., liquid-assisted grinding, LAG) permits facile, room-temperature transformation of safer metal oxide, carbonate, or hydroxide reactants into MOFs, resulting in cleaner, more atom-efficient processes that avoid external bases and production of mineral acids or their salts as byproducts. 12,13 Indeed, MOFs can now be manufactured mechanochemically on a large scale by extrusion. 14 However, scope of mechanochemistry for making currently relevant MOFs remains modest, limited to HKUST-1 and ZIF-8. 15 We now describe the development and mechanistic investigation of a mechanochemical milling approach to Zn-MOF-74, 16 a member of the popular M-MOF-74 (CPO-27) family of materials, 17−21 from stoichiometric ZnO and 2,5-dihydroxyterephthalic acid (H 4 dhta) (Figure 1). By using the very recently introduced technique for real-time in situ X-ray powder diffraction (XRPD) monitoring, 22,23 we reveal a previously not seen mechanism of mechanochemical MOF synthesis, where the formation of a low-density metal−organic structure proceeds via a close-packed reaction intermediate.Without included guests, Zn-MOF-74 has the composition Zn 2 (H 2 O) 2 (dhta), consisting of Zn 2+ coordinated by H 4 dhta anions and water. We attempted the synthesis of Zn-MOF-74 on 1.1 mmol scale (∼400 mg, see SI) by milling ZnO and H 4 dhta in 2:1 stoichiometric ratio, using 250 μL of water as the grinding liquid. 24 The liquid-to-solid ratio (η) 25 of 0.625 μL/mg was selected based on our previous experience in LAG mechanosynthesis of open MOFs. 13a,15a In situ experiments were done at the European Synchrotron Radiation Facility (ESRF) beamline ID15B using X-rays of 0.142 Å wavelength and also at a new measurement site at the Deutsches Elektronen-Synchroton (DESY) beamline P02.1, which provided improved signal-tonoise ratio and higher resolution data by using 0.207 Å radiation. 22,23 Milling was conducted using a modified Retsch mill operating at 30 Hz, in a 14 mL poly(methy...

The distinct stacking behaviour of two related 2D covalent organic frameworks is traced back to geometric and electronic features of their building blocks. Self-complementarity and donor–acceptor-type interactions are identified as design principles to access highly crystalline COFs.

Reaction of cobalt(ii) and nickel(ii) thiocyanate with ethylisonicotinate leads to the formation of [M(NCS)(ethylisonicotinate)] with M = Co (2-Co) and M = Ni (2-Ni), which can also be obtained by thermal decomposition of M(NCS)(ethylisonicotinate) (M = Co (1-Co), Ni (1-Ni)). The crystal structure of 2-Ni was determined by single crystal X-ray diffraction. The Ni(ii) cations are octahedrally coordinated by two N and two S bonding thiocyanate anions and two ethylisonicotinate ligands and are linked by pairs of anionic ligands into dimers, that are connected into layers by single thiocyanate bridges. The crystal structure of 2-Co was refined by Rietveld analysis and is isostructural to 2-Ni. For both compounds ferromagnetic ordering is observed at 8.7 K (2-Ni) and at 1.72 K (2-Co), which was also confirmed by specific heat measurements. Similar measurements on [Co(NCS)(4-acetylpyridine)] that exhibits the same layer topology also prove magnetic ordering at 1.33 K. Constrained DFT calculations (CDFT) support the ferromagnetic interactions within the layers. The calculated exchange constants in 2-Ni were used to simulate the susceptibility by quantum Monte Carlo method. The single-ion magnetic anisotropy of the metal ions has been investigated by CASSCF/CASPT2 calculations indicating significant differences between 2-Ni and 2-Co.

Metal-Organic Frameworks Using Pre-Assembled Precursors. ChemRxiv. Preprint. Ball milling mechanochemistry enables enables targeted, rapid synthesis of mixed-metal metal-organic frameworks (MOFs) with controllable stoichiometric composition. Specifically, the use of ball milling enabled the use of pre-assembled coordination polymers of zinc, magnesium, nickel(II) and cobalt(II) as precursors in an innovative mechanochemical strategy for the deliberate assembly of mixed-metal MOF-74 materials comprised of pairs of transition of main group metals in a pre-determinmed 1:1 stoichiometric ratio, including ZnMg-, ZnCo, ZnCu, MgZn-, MgCo-, MgCa-, NiZn-,NiMg-, NiCo-, CoZn-, CoMg-and CoCu-MOF-74. While this is the first example of target-oriented MOF synthesis using mechanochemistry, it also provides an entry to controlling the stoichiometric composition of mixed-metal frameworks. File list (2) download file view on ChemRxiv manuscript_ChemRxiv.pdf (1.09 MiB) download file view on ChemRxiv SI_ChemRxiv.pdf (2.25 MiB) Mechanochemistry enables targeted synthesis of mixed-metal microporous metal-organic frameworks using pre-assembled precursors

The use of a dodecanuclear zirconium acetate cluster as a precursor enables the rapid, clean mechanochemical synthesis of high-microporosity metal-organic frameworks NU-901 and UiO-67, with surface areas up to 2250 m2 g-1. Real-time X-ray diffraction monitoring reveals that mechanochemical reactions involving the conventional hexanuclear zirconium methacrylate precursor are hindered by the formation of an inert intermediate, which does not appear when using the dodecanuclear acetate cluster as a reactant.

Porphyrin-based metal–organic frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural analysis spanning local and long-range length scales, we show that PCN-221 consists of Zr6O4(OH)4 clusters in four distinct orientations within the unit cell, rather than Zr8O6 clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (dPCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster–linker binding. Our work thus introduces a new perspective on network topology and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties.

The choice of milling assembly (jar and ball material, number and size of balls) can be used to direct polymorphism in mechanochemical cocrystallisation, enabling the selective synthesis, and even reversible interconversion of cocrystal polymorphs.

Tetratopic porphyrin-based MOFs represent a particularly interesting subclass of zirconium MOFs due to the occurrence of several divergent topologies. The control over the target topology is a demanding task and reports often show products containing phase contamination. We demonstrate how mechanochemistry can be exploited for controlling the polymorphism in 12-coordinated porphyrinic zirconium MOFs, gaining pure hexagonal (shp) PCN-223 and cubic (ftw) MOF-525 phases in 20-60 minutes of milling. The reactions are mainly governed by the milling additives and the zirconium precursor. In situ monitoring by synchrotron powder X-ray diffraction (PXRD) revealed that specific reaction conditions resulted in the formation of MOF-525 as an intermediate, which rapidly converted to PCN-223 upon milling. Electron spin resonance (ESR) measurements revealed significant differences between the spectra of paramagnetic centers in two polymorphs, showing a potential of polymorphic Zr-MOFs as tunable supports in spintronics applications. Metal-organic frameworks (MOFs) received wide attention due to their potential for applications in gas storage 1-3 and separation, 4,5 catalysis, 6,7 drug delivery, 8 light-harvesting, 9,10 and destruction of harmful compounds such as chemical warfare agents. 11 Their superior performance stems from the existence of pores and channels enabling easy access of substrates to the active sites inside the MOF crystals. The use of MOFs as heterogeneous catalysts and catalysts supports is broadened after the introduction of Zr-MOFs based on zirconium [Zr6(OH)4O4] 12+ oxo-clusters and carboxylate linkers, 12 which provided a way to overcome challenges related to the robustness of MOFs under humid, acidic or basic media. 11,13 They also drew significant interest in an area of MOF-polymorphism. Zr-MOFs based on tetratopic tetrakis(4-carboxyphenyl) porphyrin (TCPP) linkers displayed unprecedented flexibility in topological ordering. They are known to exist in six different topologies, 14,15-22 12-connected cubic ftw (MOF-525) 21 and hexagonal shp (PCN-223), 16 8-connected sqc (PCN-225), 17 csq (PCN-222/MOF-545), 19,21 and scu (NU-902), 15 and 6-connected she (PCN-224). 20 Recent studies have been focused on establishing different reaction