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...

We report on the discovery and characterization of ice β-XV, which represents the second hydrogen ordered polymorph related to ice VI.

Covalent organic frameworks have emerged as a powerful synthetic platform for installing and interconverting dedicated molecular functions on a crystalline polymeric backbone with atomic precision. Here, we present a novel strategy to directly access amine-linked covalent organic frameworks, which serve as a scaffold enabling pore-wall modification and linkage-interconversion by new synthetic methods based on Leuckart−Wallach reduction with formic acid and ammonium formate. Frameworks connected entirely by secondary amine linkages, mixed amine/ imine bonds, and partially formylated amine linkages are obtained in a single step from imine-linked frameworks or directly from corresponding linkers in a one-pot crystallization-reduction approach. The new, 2D amine-linked covalent organic frameworks, rPI-3-COF, rTTI-COF, and rPy1P-COF, are obtained with high crystallinity and large surface areas. Secondary amines, installed as reactive sites on the pore wall, enable further postsynthetic functionalization to access tailored covalent organic frameworks, with increased hydrolytic stability, as potential heterogeneous catalysts.

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.