Synthesis, structural characterization, and topological rearrangement of anovel open framework U-O material: (NH4)(3)(H2O)(2) {[(UO2)(10)O-10(OH)][(UO4)(H2O)(2)]}

A novel open framework U-O material with composition (NH4)(3)(H2O)(2){[(UO2 )(10)O-10(OH)][(UO4)(H2O)(2)]} was synthesized hydrothermally. The structur e [monoclinic, a = 11.627(2) Angstrom, b = 21.161(3) Angstrom, c = 14.706(2 ) Angstrom, beta = 103.930(3)degrees, V = 3511.97 Angstrom (3)] was solved by direct methods and refined on the basis of F-2 for all 4230 unique refle ctions in space group C2/c to an agreement factor (R1) of 7.7%, calculated using 2180 unique observed reflections (\F-o\ greater than or equal to 4 si gma (F)). The structure contains six symmetrically distinct U6+ sites, five of which occur as approximately linear (UO2)(2+) uranyl ions that are coor dinated by four or five additional ligands, giving square and pentagonal bi pyramids. One U6+ cation occurs in distorted octahedral coordination. The s tructure contains beta -U3O8-type sheets parallel to (001) that are cross-l inked through U2O12 pentagonal bipyramid dimers, resulting in an open frame work structure composed only of uranium polyhedra. The (NH4)(+) and H2O gro ups are located in the interconnected three-dimensional channels along [100 ] that are bounded by 10-membered rings of uranyl polyhedra. A new layered uranyl material with composition Cs-3[(UO2)(3)O-2(OH)(3)](2)Cl(H2O)(3) was obtained by treatment of the framework phase in CsCl solution at 180 degree sC for 33 h. The structure [monoclinic, space group C2, a = 19.615(5) Angst rom, b = 7.239(2) Angstrom, c = 12.064(3) Angstrom, beta = 127.929(4)degree s, V = 1351.2(6) Angstrom (3)] was refined on the basis of F-2 using 2462 u nique reflections to R1 = 7.2%, calculated using the 1800 unique observed r eflections (\F-o\ greater than or equal to 4 sigma (F)). The structure cont ains alpha -U3O8-type sheets of uranyl pentagonal bipyramids, with two symm etrically distinct Cs cations, a single Cl anion, and two H2O groups locate d in the interlayer regions.