Munn Alexis S, Pillai Renjith S, Biswas Shyam, Stock Norbert, Maurin Guillaume, Walton Richard I
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK.
Institut Charles Gerhardt Montpellier, UMR CNRS 5253, Université Montpellier, 34095 Montpellier cedex 05, France.
Dalton Trans. 2016 Mar 14;45(10):4162-8. doi: 10.1039/c5dt03438h.
The flexibility of eight aluminium hydroxo terephthalates [Al(OH)(BDC-X)]·n(guest) (BDC = 1,4-benzene-dicarboxylate; X = -H, -CH3, -Cl, -Br, -NH2, -NO2, -(OH)2, -CO2H) crystallising in the MIL-53-type structure was investigated upon thermal dehydration of as-made samples, superhydration and methanol adsorption/desorption using in situ powder X-ray diffraction (PXRD). Profile fitting was used to determine lattice parameters as a function of time and/or temperature to describe their structural evolution. It has thus been shown that while methanol vapour adsorption induces an opening of all the modified frameworks, except the -NH2 material, superhydration only leads to open structures for Al-MIL-53-NO2, -Br and -(OH)2. All the MIL-53 solids, except Al-MIL-53-(OH)2 are present in the open structures upon thermal dehydration. In addition to the exploration of the breathing behavior of this MIL-53 series, the issue of disorder in the distribution of the functional groups between the organic linkers was explored. As a typical illustration, density functional theory calculations were carried out on different structures of Al-MIL-53-Cl, in which the distribution of -Cl within two adjacent BDC linkers is varied. The results show that the most energetically stable configuration leads to the best agreement with the experimental PXRD pattern. This observation supports that the distribution of the selected linker substituent in the functionalised solid is governed by energetics and that there is a preference for an ordering of this arrangement.
利用原位粉末X射线衍射（PXRD）研究了8种具有MIL-53型结构的氢氧化对苯二甲酸铝[Al(OH)(BDC-X)]·n(客体)（BDC = 1,4-苯二甲酸；X = -H、-CH3、-Cl、-Br、-NH2、-NO2、-(OH)2、-CO2H）在制备态样品热脱水、超水化以及甲醇吸附/脱附过程中的灵活性。通过轮廓拟合确定晶格参数随时间和/或温度的变化，以描述其结构演变。结果表明，虽然甲醇蒸汽吸附会使除-NH2材料外的所有改性骨架打开，但超水化仅会使Al-MIL-53-NO2、-Br和-(OH)2形成开放结构。除Al-MIL-53-(OH)2外，所有MIL-53固体在热脱水后均呈现开放结构。除了探索该MIL-53系列的呼吸行为外，还探讨了有机连接体之间官能团分布的无序问题。作为一个典型例子，对Al-MIL-53-Cl的不同结构进行了密度泛函理论计算，其中两个相邻BDC连接体中-Cl的分布有所不同。结果表明，能量最稳定的构型与实验PXRD图谱的吻合度最佳。这一观察结果支持了功能化固体中所选连接体取代基的分布受能量控制，且这种排列存在有序化的偏好。
