dTwo polymorphs of Cs-2(UO2)(2)(MoO4)(3) have been synthesized by hydrothermal (alpha-phase) and high-temperature (beta-phase) routes. Both were characterized by single-crystal X-ray diffraction: alpha-Cs-2(UO2)(2)(MoO4)(3), orthorhombic, Pna2(1), a = 20.4302(15) Angstrom, b = 8.5552(7) Angstrom, c = 9.8549(7) Angstrom, Z = 4; beta-Cs-2(UO2)(2)(MoO4)(3), tetragonal, P4(2)/n, a = 10.1367(8) Angstrom, c = 16.2831(17) Angstrom, Z = 4, The structures of both phases consist of linked UO7 pentagonal bipyramids and MoO4 tetrahedra: alpha-Cs-2(UO2)(2)(MoO4)(3) is a framework compound with large channels parallel to the c axis. Two cesium sites are located in these channels and are coordinated by 8 and 10 oxygen atoms. The structure of beta-Cs-2(UO2)(2)(MoO4)(3) contains corrugated [(UO2)(2)(MoO4)(3)] sheets that are parallel to (001). The cesium cations are located between the sheets and are coordinated by eight oxygen atoms, The structures are topologically related; both can be described in terms of chains of 5-connected UO7 pentagonal bipyramids and 3- and 4-connected MoO4 tetrahedra.