Abstract
Mechanochemical synthesis has recently emerged as a scalable “green” approach for the preparation of MOFs, but current understanding of the underlying reaction mechanisms is limited. In this work, an investigation of the reaction pathway of the mechanochemical synthesis of MOF-74 from ZnO and 2,5-dihydroxyterephthalic acid (H4HDTA), using DMF as a liquid additive, is presented. The complex reaction pathway involves the formation of four short-lived intermediate phases, prior to the crystallization of MOF-74. The crystal structures of three of these intermediates have been determined using a combination of single-crystal and powder X-ray diffraction methods and are described here. The initial stages of the reaction are very fast, with a DMF solvate of H4HDTA forming after only 2 min of milling. This is followed by crystallization, after only 4 min of milling, of a triclinic one-dimensional coordination polymer, Zn(H2DHTA)(DMF)2(H2O)2, which converts into a monoclinic polymorph on additional milling. Highly crystalline MOF-74 appears after prolonged milling, for at least 70 min.
Highlights
Metal−organic frameworks (MOFs) are a fascinating class of porous materials with a host of potential applications, ranging from drug delivery[1−4] to catalysis[5−7] and gas separation and storage.[8−10] In academic research, MOF synthesis is dominated by solvothermal methods, which offer low space− time yields and often require expensive organic solvents,[11] making them unsuitable for industrial production
Small amounts of liquid additives can influence the pathway of the reaction, as exemplified by the synthesis of HKUST-1, for which two previously undetected intermediate phases containing a mononuclear copper core have been identified, depending on the milling conditions and the additives used.[25]
We demonstrate that the mechanosynthesis of MOF
Summary
Metal−organic frameworks (MOFs) are a fascinating class of porous materials with a host of potential applications, ranging from drug delivery[1−4] to catalysis[5−7] and gas separation and storage.[8−10] In academic research, MOF synthesis is dominated by solvothermal methods, which offer low space− time yields and often require expensive organic solvents,[11] making them unsuitable for industrial production. The development of synthetic strategies that enable industrial manufacturing of MOFs at the required scale and cost is essential for the exploitation of these materials in new technologies.[12] Mechanochemistry, a synthetic approach in which chemical reactions occur by grinding or milling in the absence of or with little solvent,[13,14] has emerged as a scalable “green” alternative to solvothermal synthesis. The Cambridge Structural Database or the Inorganic Crystal Structure Database can be used for the identification of previously reported phases,[26] while for previously unreported phases, structure-solution methods using powder diffraction data can be exploited
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