Niekiel Felicitas, Lannoeye Jeroen, Reinsch Helge, Munn Alexis S, Heerwig Andreas, Zizak Ivo, Kaskel Stefan, Walton Richard I, de Vos Dirk, Llewellyn Philip, Lieb Alexandra, Maurin Guillaume, Stock Norbert
Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel , Max-Eyth-Straße 2, 24118 Kiel, Germany.
Inorg Chem. 2014 May 5;53(9):4610-20. doi: 10.1021/ic500288w. Epub 2014 Apr 10.
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 "breathing" 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-) 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 "breathing".
铝基金属有机框架材料CAU - 13（[Al(OH)(反式 - CDC)]；反式 - H2CDC = 反式 - 1,4 - 环己烷二甲酸）在结构上与以“呼吸”行为而闻名的MIL - 53化合物相关，即框架在外部刺激（如吸附质分子的存在）下的灵活性。详细研究了CAU - 13的吸附性能。记录了N2、H2、CH4、CO、CO2和水的吸附等温线，并通过微量量热法测定了气体的吸附焓。利用原位同步辐射粉末X射线衍射（PXRD）跟踪了CO2吸附时的结构变化。通过参数化晶胞精修分析衍射图谱，并通过密度泛函理论计算对CO2分子的优先排列进行建模。从均三甲苯中吸附和分离邻二甲苯、间二甲苯和对二甲苯的混合物显示出对邻二甲苯的优先吸附。根据PXRD数据确定了负载邻/间/对二甲苯的CAU - 13的结构。二甲苯异构体的吸附诱导的孔径开口比CAU - 13热活化时的更大。在活化样品CAU - 13（空孔）的晶体结构中，一半的连接体采用a,a构象，另一半采用e,e构象，并且a,a - CDC(2 - )离子的存在阻碍了CAU - 13的结构灵活性。然而，在吸附二甲苯后，所有连接体均以e,e构象存在，通过这种新型的“呼吸”作用允许更宽的孔径开口。
