Accelerated aging: a low energy, solvent-free alternative to solvothermal and mechanochemical synthesis of metal–organic materials

Abstract

We describe a conceptually novel ''accelerated aging'' approach for the synthesis of metal-organic materials. This approach, inspired by natural mineral weathering processes, enables the synthesis of metal-organic structures from simple and inexpensive solid reactants upon exposure to catalytic amounts of an ammonium salt under conditions of high humidity and mild temperatures (up to 45 C). Accelerated aging exploits the inherent mobility of molecules and is entirely different from solutionbased (precipitation, solvothermal synthesis) or other solvent-free (mechanochemical synthesis) approaches to metal-organic materials that require either bulk solvent and/or thermo-or mechanochemical intervention. The present proof-of-principle study of accelerated aging demonstrates the catalysed and topologically specific transformation of ZnO into unusual close-packed varieties of zeolitic imidazolate frameworks (ZIFs) in a static, non-agitated reaction mixture. The reactivity is readily scaled up, as demonstrated by performing selected syntheses of quartz-and diamondoidtopology close-packed ZIFs in ten gram amounts. The latter framework, previously obtained only by using a large excess of reagents under hydrothermal conditions, is transformed into the well-known open framework ZIF-8 by exposure to methanol vapours at room temperature, suggesting an alternative to both solvothermal and mechanochemical approaches to these materials. A tentative proton-transfer mechanism underpinning the catalytic effect in accelerated aging is proposed, involving protonated imidazole as an intermediate.

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

“…Moreover, organic solvents may interact with ZIF-8, and thus reside in the particle which are difficult to be removed in the subsequent separation processes. 26 Other methods have since been developed, such as mechanochemistry, 27 microwave, 28 ultrasonic method 29 and micro-emulsion synthesis. 30 However, the operation is relatively complex and oen needs appropriate special techniques to assist the synthesis.…”

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

“…On the contrary to the solution synthesis, aliquots sampling from the milling jars implied stopping the milling process for 1-2 minutes. As one could suggest that coupling reactions could be continuing even without milling [27][28][29][30], these short pauses were considered as reaction time. As a consequence, the effective milling time was shorter than the reaction time (see Supporting Information File 1 for details).…”

Chapter 7. Ball-milling Mechanochemical Synthesis of Coordination Bonds: Discrete Units, Polymers and Porous Materials

“…While the synthesis of pillared MOFs using ILAG clearly reveals an anion-related effect, ZIF synthesis strongly depends on the use of weakly acidic ammonium salts. 54,79 The topological control in ILAG synthesis of ZIFs appears to arise from the ability of salt additives to control the rate of spontaneous interconversion of porous and non-porous structures, rather than from specific structuretemplating effects. 79 The described mechanochemical methodologies have obvious advantages over solvothermal approaches used for porous MOF synthesis in terms of time (minutes versus days), temperature (near room-temperature versus 100-150 1C) and reactant choice (metal oxides versus soluble salts).…”

“…54,79 The topological control in ILAG synthesis of ZIFs appears to arise from the ability of salt additives to control the rate of spontaneous interconversion of porous and non-porous structures, rather than from specific structuretemplating effects. 79 The described mechanochemical methodologies have obvious advantages over solvothermal approaches used for porous MOF synthesis in terms of time (minutes versus days), temperature (near room-temperature versus 100-150 1C) and reactant choice (metal oxides versus soluble salts). Further advantages are the absence of bulk solvent and a wide choice of catalytic liquid phases, including ethanol, which is one of the more preferred solvents from a green chemistry perspective.…”