Chiral open-framework uranyl molybdates

Abstract: Two new chiral open-framework uranyl molybdates, (UO2)0.82[C8H20N]0.36[(UO2)6(MoO4)7(H2O)2](H2O)n (1) and [C6H14N2][(UO2)6(MoO4)7(H2O)2](H2O)m (2) have been synthesized by hydrothermal methods. The structures of 1 and 2 have been refined using X-ray diffraction data collected at −127°C. The structure of 1 [orthorhombic, C2221, a=12.2303(15), b=18.966(2), c=22.392(3) Å, V=5194.0(11) Å3] has been refined to R1=0.043 on the basis of 4126 unique observed reflections. The structure of 2 [orthorhombic, C2221, a=11.3256(15), b=19.860(3), c=23.731(3) Å, V=5337.8(12) Å3] has been refined to R1=0.056 on the basis of 3519 unique observed reflections. The structures of 1 and 2 are based upon complex chiral [(UO2)6(MoO4)7(H2O)2] frameworks of corner-sharing UO7 bipyramids and MoO4 tetrahedra. In addition to framework U sites, the structure of 1 contains an additional, partially-occupied and disordered U(4) site, located within the framework cavities and coordinated by several disordered anions to form the complex [(UO2)(H2O)5]2+ cation. The structure of 2 contains disordered DABCO (1,4-diazabicyclo[2.2.2]-octane) molecules. The geometrical parameters of the uranyl molybdate frameworks in the structures of 1 and 2 are significantly different. The a parameter of 1 is about 0.9Å longer than that of 2, whereas the b and c parameters of 1 are shorter than those of 2 (∼0.9 and 1.3Å, respectively). This occurs due to the adaptation of the [(UO2)6(MoO4)7(H2O)2]2− framework to the shape of the complex [(UO2)(H2O)5]2+ cation in 1. Analysis of the U–O–Mo bond angles of the frameworks indicates the U–O(15)–Mo and U–O(20)–Mo links are the most flexible. The transition from 2 to 1 involves an increase of the U–O(15)–Mo and U–O(20)–Mo angles from 146.7° to 169.0° and from 151° to 171°, respectively. [Copyright &y& Elsevier]