Search

Abstract: Single crystals of the new compounds Li6[(UO2)12(PO4)8(P4O13)] (1), Li5[(UO2)13(AsO4)9(As2O7)] (2), Li[(UO2)4(AsO4)3] (3) and Li3[(UO2)7(AsO4)5O)] (4) have been prepared using high-temperature solid state reactions. The crystal structures have been solved by direct methods: 1—monoclinic, C2/m, a=26.963(3)Å, b=7.063(1)Å, c=19.639(1)Å, β=126.890(4)°, V=2991.2(6)Å3, Z=2, R 1=0.0357 for 3248 unique reflections with |F 0|≥4σF ; 2—triclinic, , a=7.1410(8)Å, b=13.959(1)Å, c=31.925(1)Å, α=82.850(2)°, β=88.691(2)°, γ=79.774(3)°, V=3107.4(4)Å3, Z=2, R 1=0.0722 for 9161 unique reflections with |F 0|≥4σF ; 3—tetragonal, I 41/amd, a=7.160(3)Å, c=33.775(9)Å, V=1732(1)Å3, Z=4, R 1=0.0356 for 318 unique reflections with |F 0|≥4σF ; 4—tetragonal, , a=7.2160(5)Å, c=14.6540(7)Å, V=763.04(8)Å3, Z=1, R 1=0.0423 for 1600 unique reflections with |F 0|≥4σF . Structures of all the phases under consideration are based on complex 3D frameworks consisting of different types of uranium polyhedra (UO6 and UO7) and different types of tetrahedral T O4 anions ( T =P or As): PO4 and P4O13 in 1, AsO4 and As2O7 in 2, and single AsO4 tetrahedra in 3 and 4. In the structures of 1 and 2, UO7 pentagonal bipyramids share edges to form (UO5)∞ chains extended along the b axis in 1 and along the a axis in 2. The chains are linked via single T O4 tetrahedra into tubular units with external diameters of 11Å in 1 and 11.5Å in 2, and internal diameters of 4.1Å in 1 and 4.5Å in 2. The channels accommodate Li+ cations. The tubular units are linked into 3D frameworks by intertubular complexes. Structures of 3 and 4 are based on 3D frameworks composed on layers united by (UO5)∞ infinite chains. Cation–cation interactions are observed in 2, 3, and 4. In 2, the structure contains a trimeric unit with composition [OU(1)O]–U(13)–[OU(2)O]. In the structures of 3 and 4, T-shaped dimers are observed. In all the structures, Li+ cations are located in different types of cages and channels and compensate negative charges of anionic 3D frameworks. [Copyright &y& Elsevier]

Abstract: Four new Li uranyl phosphates and arsenates have been prepared by high-temperature solid-state reactions: α-Li[(UO2)(PO4)] (1), α-Li[(UO2)(AsO4)] (2), β-Li[(UO2)(AsO4)] (3) and Li2[(UO2)3(P2O7)2] (4). The structures of the compounds have been solved by direct methods: 1—triclinic, , a=5.0271(1)Å, b=9.8799(2)Å, c=10.8920(2)Å, α=108.282(9)°, β=102.993(8)°, γ=104.13(1)°, V=470.69(2)Å3, Z=4, R 1=0.0415 for 2786 unique reflections with |F 0|⩾4σF ; 2—triclinic, , a=5.129(2)Å, b=10.105(3)Å, c=11.080(3)Å, α=107.70(2)°, β=102.53(3)°, γ=104.74(3)°, V=501.4(3)Å3, Z=4, R 1=0.055 for 1431 unique reflections with |F 0|⩾4σ F; 3—triclinic, , a=5.051(1)Å, b=5.303(1)Å, c=10.101(1)Å, α=90.31(1)°, β=97.49(1)°, γ=105.08(1)°, V=258.80(8)Å3, Z=2, R 1=0.0339 for 2055 unique reflections with |F 0|⩾4σ F; 4—triclinic, , a=5.312(1)Å, b=6.696(1)Å, c=12.542(1)Å, α=94.532(9)°, β=99.059(8)°, γ=110.189(7)°, V=409.17(10)Å3, Z=2, R 1=0.0565 for 1355 unique reflections with |F 0|⩾4σ F. The structures of all four compounds are based upon 3-D frameworks of U and T polyhedra (T=P, As). Phases 1 and 2 are isostructural and consist of U2O12 dimers and UO6 square bipyramids linked by single TO4 tetrahedra. The structure of 3 consists of 3-D framework of corner-sharing UO6 bipyramids and AsO4 tetrahedra. In the structure of 4, the framework is composed of U2O12 dimers, UO6 bipyramids and P2O7 dimers. In all the compounds, Li+ cations reside in framework cavities. The topologies of the 3-D frameworks can be described as derivatives of the PtS (cooperite) network. [Copyright &y& Elsevier]