偏钨酸铵，(NH4)6[H2W12O40]：各种水合物种的结晶和热行为,Crystal Growth & Design

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偏钨酸铵，(NH4)6[H2W12O40]：各种水合物种的结晶和热行为
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2021-10-08 , DOI: 10.1021/acs.cgd.1c00639
Felix Eder ₁ , Matthias Weil ₁ , Wolf-Dieter Schubert ₂ , Christian Gierl-Mayer ₃

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各种含水偏钨酸铵相 (NH ₄ ) ₆ [H ₂ W ₁₂ O ₄₀ ]· X H ₂ O (AMT- X ) 以单晶形式获得，使用过饱和溶液、抗溶剂结晶和部分脱水作为策略用于晶体生长。根据实验室X射线衍射数据，X = 22、12.5、9.5、8.5、6、4和2的水相的晶体结构以及X = 12-乙醇和X = 4的共晶的晶体结构-2丙酮已被首次测定。AMT-22形成固溶体系列（NH ₄）_{6– x} K _x [H ₂ W ₁₂ O ₄₀ ]·22H ₂ O 与钾盐 (PMT-22) 无混溶间隙。其四方晶体结构显示球形α-Keggin型[H ₂ W ₁₂ O ₄₀ ] ^6–的扭曲立方密堆积排列空隙中具有无序铵 N 和水 O 原子的阴离子。其他水化程度较低的 AMT 相的晶体结构可以源自 α-Keggin 阴离子的扭曲六方棒堆积，同样带有空隙中的阳离子和结晶水分子。AMT-22 晶体的热行为显示出快速脱水，在环境条件下，AMT-9.5 作为中间体，AMT-4 作为稳定的水合物相。在进一步加热时，材料分解，逐步形成 AMT-2、AMT-1、AMT-0 和无定形相，然后在 400 °C 以上形成正交 WO ₃。市售 AMT 相之一，“(NH ₄ ) ₆ [H ₂ W ₁₂ O ₄₀ ]· X H₂ O”（X = 未指定）的水含量为X = 4，但在 AMT-4 以外的结构中结晶。因此，4-水合物表现出多晶型行为。

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Ammonium Metatungstate, (NH4)6[H2W12O40]: Crystallization and Thermal Behavior of Various Hydrous Species

Various hydrous ammonium metatungstate phases (NH₄)₆[H₂W₁₂O₄₀]·XH₂O (AMT-X) have been obtained in the form of single crystals, using supersaturated solutions, antisolvent crystallization, and partial dehydration as strategies for crystal growth. On the basis of laboratory X-ray diffraction data, the crystal structures of the hydrous phases with X = 22, 12.5, 9.5, 8.5, 6, 4, and 2 as well of the cocrystals with X = 12-ethanol and X = 4-2acetone have been determined for the first time. AMT-22 forms the solid solution series (NH₄)_6–xK_x[H₂W₁₂O₄₀]·22H₂O with the potassium salt (PMT-22) without a miscibility gap. Its tetragonal crystal structure shows a distorted cubic close-packed arrangement of the spherical α-Keggin-type [H₂W₁₂O₄₀]^6– anions with disordered ammonium N and water O atoms in the voids. The crystal structures of the other, less-hydrated AMT phases can be derived from distorted hexagonal rod packings of the α-Keggin anions, likewise with the cations and crystal water molecules in the voids. The thermal behavior of AMT-22 crystals reveals a quick dehydration, with AMT-9.5 as an intermediate and AMT-4 as a stable hydrate phase under ambient conditions. Upon further heating, the material decomposes with stepwise formation of AMT-2, AMT-1, AMT-0, and an amorphous phase, before orthorhombic WO₃ forms above 400 °C. One of the commercially available AMT phases, “(NH₄)₆[H₂W₁₂O₄₀]·XH₂O” (with X = unspecified) has a water content of X = 4 but crystallizes in a structure other than AMT-4. Consequently, the 4-hydrate shows polymorphic behavior.

更新日期：2021-11-03

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