High-Resolution Structural Characterization of Two Layered Aluminophosphates by Synchrotron Powder Diffraction and NMR Crystallographies

The syntheses and structure resolution process of two highly complex powdered aluminophosphates with an original 5:7 Al/P ratio are presented: [Al5(OH)­(PO4)3(PO3OH)4] [NH3(CH2)2NH3]2 [2H2O], compound 1, and [Al5(PO4)5(PO3OH)2] [NH3(CH2)3NH3]2 [H2O], compound 2. We have previously reported the structure of the periodic part of 1 by coupling synchrotron powder diffraction and solid-state nuclear magnetic resonance (NMR) crystallographies. With a similar strategy, that is, input of large parts of the building blocks determined by analysis of the 27Al–31P correlation pattern of the two-dimensional (2D) NMR spectrum in the structure search process, we first determine the periodic structure of 2, using the powder synchrotron diffraction data as cost function. Both 1 and 2 are layered materials, in which the inorganic layers contain five P and seven Al inequivalent atoms, with aluminum atoms that are found in three different coordination states, AlO4, AlO5, and AlO6, and the interlayer space contains the amines and water molecules. In 1, the inorganic layers are stacked on each other with a 42 element of symmetry along the c-axis, while they are stacked with a 180° rotation angle in 2. By analysis of a set of high-resolution 1D and 2D NMR spectra (31P, 27Al, 1H, 15N, 13C, 27Al–31P, 1H–31P, and 1H–14N), the structure analysis of 1 and 2 is extended beyond the strict periodicity, to which diffraction is restricted, and provides localization of the hydroxyl groups and water molecules in the frameworks and an attempt to correlate the presence of these latter species to the structural features of the two samples is presented. Finally, the dehydration/rehydration processes occurring in these solids are analyzed. The methodology of the structure determination for these dehydrated forms uses the same principles, combining X-ray powder diffraction and solid-state NMR data.本文报道了两种具有新颖5:7 Al/P比的高复杂粉末状铝磷酸盐的合成与结构解析过程：化合物1为[Al5(OH)­(PO4)3(PO3OH)4] [NH3(CH2)2NH3]2 [2H2O]，化合物2为[Al5(PO4)5(PO3OH)2] [NH3(CH2)3NH3]2 [H2O]。此前我们曾结合同步辐射粉末衍射（synchrotron powder diffraction）与固态核磁共振（solid-state nuclear magnetic resonance, NMR）晶体学，解析了化合物1的周期性结构部分。我们采用类似策略，即以二维（2D）核磁共振谱的27Al–31P相关图谱分析所得的大量结构基元（building blocks）作为结构搜索过程的输入，以粉末同步辐射衍射数据作为目标函数（cost function），率先解析了化合物2的周期性结构。化合物1和2均为层状材料，其无机层包含5个不等价（inequivalent）磷原子与7个不等价铝原子，铝原子存在三种不同配位环境（coordination states）：AlO4、AlO5与AlO6，层间空间则填充有机胺与水分子。在化合物1中，无机层沿c轴（c-axis）以42次对称元素（42 element of symmetry）堆叠，而化合物2中的无机层则以180°旋转角进行堆叠。通过对一系列高分辨一维（1D）与二维（2D）核磁共振谱（31P、27Al、1H、15N、13C、27Al–31P、1H–31P及1H–14N）进行分析，我们将化合物1与2的结构解析拓展至衍射方法所局限的严格周期性范围之外，实现了骨架中羟基与水分子的定位，并尝试将上述物种的存在与两个样品的结构特征相关联。最后，我们对这些固体材料所发生的脱水/复水过程进行了分析。针对这些脱水样品的结构解析方法采用了相同的原理，即结合X射线粉末衍射（X-ray powder diffraction）与固态核磁共振数据开展研究。