CRYSTAL CHEMISTRY OF URANYL MOLYBDATES. VIII. CRYSTAL STRUCTURES OF Na3Tl3[(UO2)(MoO4)4], Na13–xTl3+x[(UO2)(MoO4)3]4(H2O)6+x (x = 0.1), Na3Tl5[(UO2)(MoO4)3]2(H2O)3 AND Na2[(UO2)(MoO4)2](H2O)4

Crystals of four sodium uranyl molybdates, Na3Tl3[(UO2)(MoO4)4] (1), Na13–xTl3+x[(UO2)(MoO4)3]4(H2O)6+x (x = 0.1) (2), Na3Tl5[(UO2)(MoO4)3]2(H2O)3 (3) and Na2[(UO2)(MoO4)2](H2O)4 (4), have been synthesized by hydrothermal methods. The structure of each was solved and refined on the basis of F2 for all unique data collected using MoK X-radiation and a CCD-based detector. The structure of 1 [orthorhombic, Pbcn, a 20.5823(14), b 7.4391(5), c 26.2514(17) Å, V 4019.5(5) Å3, Z = 8] was refined to an R1 of 0.060. It is based upon a finite cluster with composition [(UO2)2(MoO4)8] that contains two UrO5 pentagonal bipyramids and eight MoO4 tetrahedra. The clusters are linked into a framework through distorted Na(1)O6 and Na(2)O6 octahedra. The Tl atoms and partially occupied Na(3) and Na(4) sites are located within cavities in the framework. The structure of 2 [monoclinic, P2/c, a 19.7942(11), b 7.1913(4), c 22.8835(13) Å, 97.828(1)o, V 3227.0(3) Å3, Z = 2] was refined to an R1 of 0.050. It contains chains of composition [(UO2)(MoO4)3] that are parallel to the a axis. The chains are linked into a threedimensional framework by Na 5 and Na 6 polyhedra ( : O2–, H2O) that share edges. The Tl atoms are located in cavities within the framework. The structure of 3 [orthorhombic, P212121, a 10.7662(6), b 11.9621(6), c 12.8995(7) Å, V 1661.3(2) Å3, Z = 2] was refined to an R1 of 0.063. It is based on chains of composition [(UO2)(MoO4)3] parallel to the c axis that are linked into a framework by Na(1) 6 octahedra. The Tl atoms and partially occupied Na(2) sites are located in cavities within the framework. The structure of 4 [monoclinic, P21/n, a 8.9023(5), b 11.5149(6), c 13.8151(7) Å, 107.743(1)o, V 1348.8(1) Å3, Z = 4] was refined to an R1 of 0.035. It contains sheets of composition [(UO2)(MoO4)2] that are parallel to the (1̄01) plane. Na 6 octahedra share edges with each other, giving chains parallel to the b axis that link adjacent [(UO2)(MoO4)2] sheets into a framework. The four structures are compared to those of related uranyl molybdates.