Chiral open-framework uranyl molybdates.: 2.: Flexibility of the U:Mo=6:7 frameworks:: syntheses and crystal structures of (UO2)0.82[C8H20N]0.36[(UO2)6(MoO4)7(H2O)2](H2O)n and [C6H14N2][(UO2)6(MoO4)7(H2O)2](H2O)m

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 -127degreesC. The structure of 1 [orthorhombic, C222(1), a = 12.2303(15) b = 18.966(2) c = 22.392(3) Angstrom, V = 5194.0(11) Angstrom(3)] has been refined to R-1 = 0.043 on the basis of 4126 unique observed reflections. The structure of 2 [orthorhombic, C222(1), a = 11.3256(15), b = 19.860(3), c = 23.731(3) Angstrom, V = 5337.8(12) Angstrom(3)] has been refined to R-1 = 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 [(UO7)(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 0.9 Angstrom longer than that of 2, whereas the b and c parameters of 1 are shorter than those of 2 (similar to0.9 and 1.3 Angstrom, 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 146.7degrees to 169.0degrees and from 151degrees to 171degrees, respectively. (C) 2004 Elsevier Inc. All rights reserved.