High-Temperature, High-Pressure Hydrothermal Synthesis, Characterization, and Structural Relationships of Layered Uranyl Arsenates

Five new uranyl arsenates, Na₁₄[(UO₂)₅(AsO₄)₈]·2H₂O (<b>1</b>), K₆[(UO₂)₅O₅(AsO₄)₂] (<b>2a</b>), K₄[(UO₂)₃O₂(AsO₄)₂] (<b>2b</b>), Rb₄[(UO₂)₃O₂(AsO₄)₂] (<b>3</b>), and Cs₆[(UO₂)₅O₂(AsO₄)₄] (<b>4</b>), were synthesized by high-temperature, high-pressure hydrothermal reactions at about 560 °C and 1440 bar and were characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and photoluminescence spectroscopy. Crystal data for compound <b>1</b>: triclinic, <i>P</i>1̅, <i>a</i> = 7.0005(3) Å, <i>b</i> = 12.1324(4) Å, <i>c</i> = 13.7428(5) Å, α = 64.175(2)°, β = 89.092(2)°, γ = 85.548(2)°, <i>V</i> = 1047.26(7) ų, <i>Z</i> = 1, <i>R</i>1 = 0.0185; compound <b>2a</b>: monoclinic, <i>P</i>2₁/<i>c</i>, <i>a</i> = 6.8615(3) Å, <i>b</i> = 24.702(1) Å, <i>c</i> = 7.1269(3) Å, β = 98.749(2)°, <i>V</i> = 1193.89(9) ų, <i>Z</i> = 2, <i>R</i>1 = 0.0225; compound <b>2b</b>: monoclinic, <i>P</i>2₁/<i>c</i>, <i>a</i> = 6.7852(3) Å, <i>b</i> = 17.3640(8) Å, <i>c</i> = 7.1151(3) Å, β = 98.801(3)°, <i>V</i> = 828.42(6) ų, <i>Z</i> = 2, <i>R</i>1 = 0.0269; compound <b>3</b>: monoclinic, <i>P</i>2₁/<i>m</i>, <i>a</i> = 6.9783(3) Å, <i>b</i> = 17.4513(8) Å, <i>c</i> = 7.0867(3) Å, β = 90.808(3)°, <i>V</i> = 862.94(7) ų, <i>Z</i> = 2, <i>R</i>1 = 0.0269; compound <b>4</b>: triclinic, <i>P</i>1̅, <i>a</i> = 7.7628(3) Å, <i>b</i> = 9.3324(4) Å, <i>c</i> = 11.9336(4) Å, α = 75.611(2)°, β = 73.136(2)°, γ = 86.329(2)°, <i>V</i> = 801.37(5) ų, <i>Z</i> = 1, <i>R</i>1 = 0.0336. The five compounds have layer structures consisting of uranyl square, pentagonal, and hexagonal bipyramids as well as AsO₄ tetrahedra. Compound <b>1</b> contains chains of discrete uranyl square and pentagonal bipyramids, <b>2a</b> contains three-polyhedron-wide ribbons of edge- and corner-sharing uranyl square and pentagonal bipyramids, <b>2b</b> and <b>3</b> contain dimers of edge-shairing pentagonal bipyramids that share edges with hexagonal bipyramids to form chains, and <b>4</b> contains one-polyhedron-wide zigzag chains of edge-sharing uranyl polyhedra. The double sheet structure of <b>1</b> is new, but the chain topology has been observed in an organically templated uranyl sulfate. Compound <b>2b</b> is a new geometrical isomer of the phosphuranylite group. The sheet anion topologies of <b>2a</b> and <b>4</b> can be obtained by splitting the β-U₃O₈-type sheet into complex chains and connecting the chains by arsenates