Enclathration and Confinement of Small Gases by the Intrinsically 0D Porous Molecular Solid, Me,H,SiMe2

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• 作者：Christopher M. Kane ; Arash Banisafar ; Timothy P. Dougherty ; Leonard J. Barbour ; K. Travis Holman
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：April 6, 2016
• 年：2016
• 卷：138
• 期：13
• 页码：4377-4392
• 全文大小：823K
• ISSN：1520-5126

文摘

The stable, guest-free crystal form of the simple molecular cavitand, Me,H,SiMe₂, is shown to be intrinsically porous, possessing discrete, zero-dimensional (0D) pores/microcavities of about 28 ų. The incollapsible 0D pores of Me,H,SiMe₂ have been exploited for the enclathration and room temperature (and higher) confinement of a wide range of small gases. Over 20 isostructural x(gas/guest)@Me,H,SiMe₂ (x ≤ 1) clathrates (guest = H₂O, N₂, Ar, CH₄, Kr, Xe, C₂H₄, C₂H₆, CH₃F, CO₂, H₂S, CH₃Cl, CH₃OCH₃, CH₃Br, CH₃SH, CH₃CH₂Cl, CH₂Cl₂, CH₃I, CH₃OH, BrCH₂Cl, CH₃CH₂OH, CH₃CN, CH₃NO₂, I₂), and a propyne clathrate (CH₃CCH@Me,H,SiMe₂·2CHCl₃), have been prepared and characterized, and their single crystal structures determined. Gas enclathration is found to be highly selective for gases that can be accommodated by the predefined, though slightly flexible 0D pore. The structure determinations provide valuable insight, at subangstrom resolution, into the factors that govern inclusion selectivity, gas accommodation, and the kinetic stability of the clathrates, which has been probed by thermal gravimetric analysis. The activation (emptying) of several clathrates (guest = H₂O, N₂, CO₂, Kr, CH₃F) is shown to occur in a single-crystal-to-single-crystal (SC → SC) fashion, often requiring elevated temperatures. Akin to open pore materials, water vapor and CO₂ gas are shown to be taken up by single crystals of empty Me,H,SiMe₂ at room temperature, but sorption rates are slow, occurring over weeks to months. Thus, Me,H,SiMe₂ exhibits very low, but measurable, gas permeability, despite there being no obvious dynamic mechanism to facilitate gas uptake. The unusually slow exchange kinetics has allowed the rates of gas (water vapor and CO₂) sorption to be quantified by single crystal X-ray diffraction. The data are well fit to a simple three-dimensional diffusion model.