Non-porous organic crystals and their interaction with guest molecules from the gas phase

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 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 non-porous to argon.

Kinetic or Thermodynamic Product? Case Studies on the Formation of Regioisomers of Tetraphenyladamantanes

“…Some tetraaryladamantane ethers have attracted inte­rest because of their ability to include other molecules in their crystalline lattice. 24 25 26 27 28 29 30 31 32 Building on earlier work on diaryladamantanes 17 we recently showed that 1,3,5,7-tetrakis(2,4-dimethoxyphenyl)adamantane (TDA), 1,3,5,7-tetrakis(2,4-diethoxyadamantane (TEO), and 1,3,5,7-tetrakis(2-bromo-4-methoxyphenyl)adamantane (TBro) are able to act as crystalline hosts for liquid compounds. This property makes them useful as crystalline coats for hazardous or reactive compounds, 30 or reversible uptake of volatile organic compounds from the gas phase.…”

“…This property makes them useful as crystalline coats for hazardous or reactive compounds, 30 or reversible uptake of volatile organic compounds from the gas phase. 31 Further, either of these TAAs can be used as crystallization chaperones to determine the absolute configuration of small molecules that are liquids at room temperature. 32 The tetraaryladamantanes mentioned above can be synthesized by a route adapted from the work of Stetter, [19][20][21][22] starting with four-fold bromination of adamantane in the presence of a strong Lewis acid.…”

“…This property makes them useful as crystalline coats for hazardous or reactive compounds, 30 or reversible uptake of volatile organic compounds from the gas phase. 31 Further, either of these TAAs can be used as crystallization chaperones to determine the absolute configuration of small molecules that are liquids at room temperature. 32…”

Controllable Structural Transformation of Non‐Porous Propyl‐Malonate Hexakis[60]fullerene by Chloroform Uptake/Release

“…Engineered organic molecular crystals are steadily gaining attention in the adsorption field, where conventionally nanoporous materials are playing a leading role. [1] Compared to COFs and MOFs, which commonly tend to contain pores in their crystal structures [2][3][4][5][6][7] direct assembly of discrete organic molecules giving rise to porous structures is challenging. Generally, they tend to pack efficiently to maximize attractive intermolec-ular contacts and minimize voids in the crystal lattice, giving rise to stable assemblies.…”

“…Engineered organic molecular crystals are steadily gaining attention in the adsorption field, where conventionally nanoporous materials are playing a leading role [1] . Compared to COFs and MOFs, which commonly tend to contain pores in their crystal structures [2–7] direct assembly of discrete organic molecules giving rise to porous structures is challenging.…”