Non-porous organic crystals and their interaction with guest molecules from the gas phase
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Non-porous organic crystals and their interaction with guest molecules from the gas phase Mirian Elizabeth Casco1 · Felix Krupp2 · Sven Grätz3 · Alexander Schwenger2 · Vassiliki Damakoudi2 · Clemens Richert2 · Wolfgang Frey2 · Lars Borchardt3 Received: 6 April 2020 / Revised: 16 July 2020 / Accepted: 25 August 2020 © The Author(s) 2020
Abstract Some organic molecules encapsulate solvents upon crystallization. One class of compounds that shows a high propensity to form such crystalline solvates are tetraaryladamantanes (TAAs). Recently, tetrakis(dialkoxyphenyl)-adamantanes have been shown to encapsulate a wide range of guest molecules in their crystals, and to stabilize the guest molecules against undesired reactions. The term ‘encapsulating organic crystals’ (EnOCs) has been coined for these species. In this work, we studied the behavior of three TAAs upon exposition to different guest molecules by means of sorption technique. We firstly measured the vapor adsorption/desorption isotherms with water, tetrahydrofuran and toluene, and secondly, we studied the uptake of methane on dry and wet TAAs. Uptake of methane beyond one molar equivalent was detected for wet crystals, even though the materials showed a lack of porosity. Thus far, such behavior, which we ascribe to methane hydrate formation, had been described for porous non-crystalline materials or crystals with detectable porosity, not for non-porous organic crystals. Our results show that TAA crystals have interesting properties beyond the formation of conventional solvates. Gas-containing
Mirian Elizabeth Casco and Felix Krupp contributed equally to this study. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10450-020-00259-8) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
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Adsorption
organic crystals may find application as reservoirs for gases that are difficult to encapsulate or are slow to form crystalline hydrates in the absence of a host compound. Wet tetraaryladamantane crystals take up methane in form of methane hydrate structure I, even though they appear nonporous to argon.
Keywords Adamantane · Adsorption isotherms · Methane hydrate
1 Introduction Rationally designed organic molecular crystals are gaining more and more significance in the adsorption fields (e.g. gas storage and separation) (Thallapally et al. 2007; Enright et al. 2003), where traditionally nanoporous materials including carbons, silica, zeolites and, recently, covalentorganic framework (COFs) and metal-organic framework (MOFs) are protagonists (Schüth et al. 2002). Unlike COFs and MOFs, which contain stable and extended nanoporous networks synthesized from organic molecular precursors (Chaoui et al. 2017; Zhou et al. 2012), the direct assembly of discrete organic molecules into porous structures is challenging; because they tend to pack efficiently to maximize the attractive intermolecular contact and t
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