MOLYBDATE UNITS IN THE STRUCTURES OF Cs4[(UO2)3O(MoO4)2(MoO5)] AND Cs6[(UO2)(MoO4)4]

Two Cs uranyl molybdates, Cs4[(UO2)3O(MoO4)2(MoO5)] and Cs6[(UO2)(MoO4)4], have been synthesized by high-temperature solid-state reactions. The structures of these compounds were solved by direct methods and refined on the basis of F2 for all unique data collected with monochromatic MoK X-radiation and a CCD (charge-coupled device) detector. The structure of Cs4[(UO2)3O(MoO4)2(MoO5)] was refined to an agreement factor (R1) of 4.4%, calculated using the 4873 unique observed reflections (Fo ≥ 4F). It is triclinic, space group P1, a 7.510(2), b 7.897(2), c 9.774(2) Å, 79.279(5), 81.269(5), 87.251(5)°, V 562.8(2) Å3, Z = 1. The structure of Cs6[(UO2)(MoO4)4] was refined to an R1 of 4.9%, calculated using the 4275 unique observed reflections (Fo ≥ 4F). It is triclinic, space group P¯1, a 11.613(3), b 12.545(3), c 14.466(3) Å, 102.713(6), 95.281(6), 106.182(6) o, V 1947.7(8) Å3, Z = 3. These compounds are based upon uranyl molybdate structural units not previously observed in uranyl compounds. The structure of Cs4[(UO2)3O(MoO4)2(MoO5)] contains sheets of composition [(UO2)3Mo3O14]4 – that contain UrO5 pentagonal bipyramids (Ur: uranyl ion), MoO4 tetrahedra and MoO5 polyhedra. The sheets are parallel to (100) and Cs cations are located in the interlayer. The structure of Cs6[(UO2)(MoO4)4] is based upon two symmetrically distinct finite clusters of composition [(UO2)(MoO4)4]6–, each of which contains a central UrO4 square bipyramid that shares all four of its equatorial vertices with MoO4 tetrahedra. Three-dimensional connectivity is provided by Cs cations located between the clusters