Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9617837 | Microporous and Mesoporous Materials | 2005 | 10 Pages |
Abstract
A new chiral 6:7 open-framework uranyl molybdate, [C6H16N]2[(UO2)6(MoO4)7(H2O)2](H2O)2, has been synthesized by hydrothermal methods. The structure has been refined using single-crystal X-ray diffraction data collected at 20 and â127 °C. The 20 °C structure [orthorhombic, C2221, a = 11.3045(14), b = 19.962(6), c = 24.416(5) Ã
, VÂ =Â 5510(2)Â Ã
3] has been refined to R1 = 0.046 on the basis of 6093 unique observed reflections. The â127 °C structure [orthorhombic, P212121, a = 11.211(4), b = 19.880(10), c = 24.421(8) Ã
, VÂ =Â 5443(4)Â Ã
3] has been refined to R1 = 0.047 on the basis of 6951 unique observed reflections. The structures are based upon topologically identical frameworks of corner-sharing UO7 pentagonal bipyramids and MoO4 tetrahedra. The extra-framework H2O groups and protonated triethylamine molecules reside in the framework cavities. In the C2221 structure at 20 °C, H2O and [C6H16N]+ molecules filling the chiral channels along [0 0 1] are disordered, whereas, in the P212121 structure at â127 °C, they are perfectly ordered. The symmetry difference between structures at 20 °C and â127 °C is the result of a C2221 â P212121 second order phase transition that involves ordering of extra-framework protonated amine molecules and H2O groups, and distortion of the flexible [(UO2)6(MoO4)7(H2O)2]2â uranyl molybdate framework. On the basis of measurements of intensities of reflections that violate absence conditions of C-centering cell, the temperature of the phase transition is estimated as â11 °C.
Related Topics
Physical Sciences and Engineering
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Authors
Sergey V. Krivovichev, Th. Armbruster, Dmitry Yu. Chernyshov, Peter C. Burns, Evgeniy V. Nazarchuk, Wulf Depmeier,