Synthesis, Structural Characterization, and Topological Rearrangement of a Novel Open Framework U−O Material: (NH₄)₃(H₂O)₂{[(UO₂)₁₀O₁₀(OH)][(UO₄)(H₂O)₂]}

A novel open framework U−O material with composition (NH 4 ) 3 (H 2 O) 2 {[(UO 2 ) 10 O 10 (OH)][(UO 4 )(H 2 O) 2 ]} was synthesized hydrothermally. The structure [monoclinic, a = 11.627(2) Å, b = 21.161(3) Å, c = 14.706(2) Å, β = 103.930(3)°, V = 3511.97 Å 3 ] was solved by direct methods and refined on the basis of F 2 for all 4230 unique reflections in space group C 2/ c to an agreement factor (R1) of 7.7%, calculated using 2180 unique observed reflections (| F o | ≥ 4σ F ). The structure contains six symmetrically distinct U 6+ sites, five of which occur as approximately linear (UO 2 ) 2+ uranyl ions that are coordinated by four or five additional ligands, giving square and pentagonal bipyramids. One U 6+ cation occurs in distorted octahedral coordination. The structure contains β-U 3 O 8 -type sheets parallel to (001) that are cross-linked through U 2 O 12 pentagonal bipyramid dimers, resulting in an open framework structure composed only of uranium polyhedra. The (NH 4 ) + and H 2 O groups 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 [(UO 2 ) 3 O 2 (OH) 3 ] 2 Cl(H 2 O) 3 was obtained by treatment of the framework phase in CsCl solution at 180 °C for 33 h. The structure [monoclinic, space group C 2, a = 19.615(5) Å, b = 7.239(2) Å, c = 12.064(3) Å, β = 127.929(4)°, V = 1351.2(6) Å 3 ] was refined on the basis of F 2 using 2462 unique reflections to R1 = 7.2%, calculated using the 1800 unique observed reflections (| F o | ≥ 4σ F ). The structure contains α-U 3 O 8 -type sheets of uranyl pentagonal bipyramids, with two symmetrically distinct Cs cations, a single Cl anion, and two H 2 O groups located in the interlayer regions.