Research output: Contribution to journal › Article › peer-review
A new chiral 6:7 open-framework uranyl molybdate, [C6H 16N]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 -127°C. The 20°C structure [orthorhombic, C2221; a = 11.3045(14), b = 19.962(6), c = 24.416(5)Å, V = 5510(2)Å3] has been refined to R1 = 0.046 on the basis of 6093 unique observed reflections. The -127°C structure [orthorhombic, P212 121, a = 11.211(4), b= 19.880(10), c = 24.421(8) Å, V= 5443(4)Å3] 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 [C 6H16N]+ molecules filling the chiral channels along [001] are disordered, whereas, in the P21212 1 structure at -127°C, they are perfectly ordered. The symmetry difference between structures at 20°C and -127°C is the result of a C2221 → P212121 second order phase transition that involves ordering of extra-framework protonated amine molecules and H2O groups, and distortion of the flexible [(UO 2)6(MoO4)7(H2O) 2]2- 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 -11°C.
Original language | English |
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Pages (from-to) | 225-234 |
Number of pages | 10 |
Journal | Microporous and Mesoporous Materials |
Volume | 78 |
Issue number | 2-3 |
DOIs | |
State | Published - 1 Mar 2005 |
ID: 36550351