Two novel U6+ compounds, Sr-5(UO2)(20)(UO6)(2)O-16(OH)(6)(H2O)(6) (SrFm) and Cs(UO2)(9)U3O16(OH)(5) (CsFm), have been synthesized by mild hydrothermal reactions. The structures of SrFm (orthorhombic, C222(1), a = 11.668(1), b = 21.065 (3), c = 13.273 angstrom, V = 3532.5(1) angstrom(3), Z = 2) and CsFm (trigonal, R (3) over barc, a = 11.395(2), c = 43.722(7) angstrom, V = 4916.7(1) angstrom(3), Z = 6) are rare examples of uranyl compounds that contain cation-cation interactions where an O atom of one uranyl ion is directly linked to another uranyl ion. Both structures are complex frameworks. SrFm contains sheets of polyhedra that are linked through cation-cation interactions with uranyl ions located between the sheets. CsFm possesses an unusually complex framework of vertex- and edge-sharing U6+ polyhedra that incorporates cation-cation interactions.