Conformation-Controlled Sorption Properties and Breathing of the Aliphatic Al-MOF [Al(OH)(CDC)]

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• 作者：Felicitas Niekiel ; Jeroen Lannoeye ; Helge Reinsch ; Alexis S. Munn ; Andreas Heerwig ; Ivo Zizak ; Stefan Kaskel ; Richard I. Walton ; Dirk de Vos ; Philip Llewellyn ; Alexandra Lieb ; Guillaume Maurin ; Norbert Stock
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：May 5, 2014
• 年：2014
• 卷：53
• 期：9
• 页码：4610-4620
• 全文大小：593K
• 年卷期：v.53,no.9(May 5, 2014)
• ISSN：1520-510X

文摘

The Al-MOF CAU-13 ([Al(OH)(trans-CDC)]; trans-H₂CDC = trans-1,4-cyclohexanedicarboxylic acid) is structurally related to the MIL-53 compounds that are well-known for their 鈥渂reathing鈥?behavior, i.e., the framework flexibility upon external stimuli such as the presence of adsorbate molecules. The adsorption properties of CAU-13 were investigated in detail. The sorption isotherms of N₂, H₂, CH₄, CO, CO₂, and water were recorded, and the adsorption enthalpies for the gases were determined by microcalorimetry. The structural changes upon adsorption of CO₂ were followed with in situ synchrotron powder X-ray diffraction (PXRD). The patterns were analyzed by parametric unit cell refinement, and the preferential arrangement of the CO₂ molecules was modeled by density functional theory calculations. The adsorption and separation of mixtures of o-, m-, and p-xylene from mesitylene showed a preferred adsorption of o-xylene. The structures of o/m/p-xylene-loaded CAU-13 were determined from PXRD data. The adsorption of xylene isomers induces a larger pore opening than that in the thermal activation of CAU-13. In the crystal structure of the activated sample CAU-13(empty pore), half of the linkers adopt the a,a confirmation and the other half the e,e conformation, and the presence of a,a-CDC^{2鈥?/sup> ions hampers the structural flexibility of CAU-13. However, after the adsorption of xylene, all linkers are present in the e,e conformation, allowing for a wider pore opening by this new type of 鈥渂reathing鈥?}