Pore with Gate: Enhancement of the Isosteric Heat of Adsorption of Dihydrogen via Postsynthetic Cation Exchange in Metal鈭扥rganic Frameworks

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• 作者：Sihai Yang ; Gregory S. B. Martin ; Jeremy J. Titman ; Alexander J. Blake ; David R. Allan ; Neil R. Champness ; Martin Schr枚der
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：October 3, 2011
• 年：2011
• 卷：50
• 期：19
• 页码：9374-9384
• 全文大小：1413K
• 年卷期：v.50,no.19(October 3, 2011)
• ISSN：1520-510X

文摘

Three isostructural anionic frameworks {[(Hdma)(H₃O)][In₂(L¹)₂]路4DMF路5H₂O}_{鈭?/sub> (NOTT-206-solv), {[H2ppz][In2(L²)2]路3.5DMF路5H2O}鈭?/sub> (NOTT-200-solv), and {[H2ppz][In2(L³)2]路4DMF路5.5H2O}鈭?/sub> (NOTT-208-solv) (dma = dimethylamine; ppz = piperazine) each featuring organic countercations that selectively block the channels and act as pore gates have been prepared. The organic cations within the as-synthesized frameworks can be replaced by Li⁺ ions to yield the corresponding Li⁺-containing frameworks {Li1.2(H3O)0.8[In2(L¹)2]路14H2O}鈭?/sub> (NOTT-207-solv), {Li1.5(H3O)0.5[In2(L²)2]路11H2O}鈭?/sub> (NOTT-201-solv), and {Li1.4(H3O)0.6[In2(L³)2]路4acetone路11H2O}鈭?/sub> (NOTT-209-solv) in which the pores are now unblocked. The desolvated framework materials NOTT-200a, NOTT-206a, and NOTT-208a display nonporous, hysteretic and reversible N2 uptakes, respectively, while NOTT-206a and NOTT-200a provide a strong kinetic trap showing adsorption/desorption hysteresis with H2. Single crystal X-ray analysis confirms that the Li⁺ ions are either tetrahedrally (in NOTT-201-solv and NOTT-209-solv) or octahedrally (in NOTT-207-solv) coordinated by carboxylate oxygen atoms and/or water molecules. This is supported by ⁷Li solid-state NMR spectroscopy. NOTT-209a, compared with NOTT-208a, shows a 31% enhancement in H2 storage capacity coupled to a 38% increase in the isosteric heat of adsorption to 12 kJ/mol at zero coverage. Thus, by modulating the pore environment via postsynthetic cation exchange, the gas adsorption properties of the resultant MOF can be fine-tuned. This affords a methodology for the development of high capacity storage materials that may operate at more ambient temperatures.}