Structures and syntheses of layered and framework amine-bearing uranyl phosphate and uranyl arsenates

Abstract

Two hydrated uranyl arsenates and a uranyl phosphate were synthesized by hydrothermal methods in the presence of amine structure-directing agents and their structures determined: (N 2C 6H 14)[(UO 2)(AsO 4)] 2(H 2O) 3, DabcoUAs, {NH(C 2H 5) 3}[(UO 2) 2(AsO 4)(AsO 3OH)], TriethUAs, and (N 2C 4H 12)(UO 2)[(UO 2)(PO 4)] 4(H 2O) 2, PiperUP. Intensity data were collected at room temperature using Mo Kα X-radiation and a CCD-based area detector. The crystal structures were refined by full-matrix least-squares techniques on the basis of F 2 to agreement indices ( DabcoUAs, TriethUAs, PiperUP) w R 2=5.6%, 8.3%, 7.2% for all data, and R 1=2.9%, 3.3%, 4.0%, calculated for 1777, 5822, 9119 unique observed reflections (| F o|⩾4 σ F), respectively. DabcoUAs is monoclinic, space group C2/ m, Z=2, a=18.581(1), b=7.1897(4), c=7.1909(4) Å, β=102.886(1)°, V=936.43(9) Å 3, D calc=3.50 g/cm 3. TriethUAs is monoclinic, space group P2 1/ n, Z=4, a=9.6359(4), b=18.4678(7), c=10.0708(4) Å, β=92.282(1)°, V=1790.7(1) Å 3, D calc=3.41 g/cm 3. PiperUP is monoclinic, space group Pn, Z=2, a=9.3278(4), b=15.5529(7), c=9.6474(5) Å, β=93.266(1)°, V=1397.3(1) Å 3, D calc=4.41 g/cm 3. The structure of DabcoUAs contains the autunite-type sheet formed by the sharing of vertices between uranyl square bipyramids and arsenate tetrahedra. The triethylenediammonium cations are located in the interlayer along with two H 2O groups and are disordered. Both TriethUAs and PiperUP contain sheets formed of uranyl pentagonal bipyramids and tetrahedra (arsenate and phosphate, respectively) with the uranophane sheet-anion topology. In TriethUAs, triethlyammonium cations are located in the interlayer. In PiperUP, the sheets are connected by a uranyl pentagonal bipyramid that shares corners with phosphate tetrahedra of adjacent sheets, resulting in a framework with piperazinium cations and H 2O groups in the cavities of the structure.