Crystal chemistry of anhydrous Li uranyl phosphates and arsenates. II. Tubular fragments and cation–cation interactions in the 3D framework structures of Li6[(UO2)12(PO4)8(P4O13)], Li5[(UO2)13(AsO4)9(As2O7)], Li[(UO2)4(AsO4)3] and Li3[(UO2)7(AsO4)5O)]

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, R1=0.0357 for 3248 unique reflections with |F0|≥4σF; 2—triclinic, P1¯, 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, R1=0.0722 for 9161 unique reflections with |F0|≥4σF; 3—tetragonal, I41/amd, a=7.160(3) Å, c=33.775(9) Å, V=1732(1) Å3, Z=4, R1=0.0356 for 318 unique reflections with |F0|≥4σF; 4—tetragonal, P4¯, a=7.2160(5) Å, c=14.6540(7) Å, V=763.04(8) Å3, Z=1, R1=0.0423 for 1600 unique reflections with |F0|≥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 TO4 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 TO4 tetrahedra into tubular units with external diameters of 11 Å in 1 and 11.5 Å in 2, and internal diameters of 4.1 Å in 1 and 4.5 Å 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.

The crystal structures of Li5[(UO2)13(AsO4)9(As2O7)] separated into tubular units and intertubular complexes.Figure optionsDownload as PowerPoint slide