Synthesis and crystal structures of M2[(UO2)3(SeO4)5](H2O)16 (MÂ =Â Co, Zn)

Crystals of two new inorganic compounds, M2[(UO2)3(SeO4)5](H2O)16 (M = Co, Zn), have been prepared by evaporation from aqueous solutions. The structures of the compounds have been determined and refined using single crystal diffraction data. The Co compound is triclinic, space group P1¯, a = 10.458(2), b = 11.032(2), c = 17.893(4) Å, α = 89.451(17), β = 90.280(17), γ = 61.761(14)°, V = 1818.5(6) Å3, R1 = 0.075 for 6611 independent observed reflections. The Zn phase is triclinic as well, space group P1¯, a = 10.438(3), b = 11.063(4), c = 17.895(6) Å, α = 89.19(3), β = 89.85(3), γ = 61.72(2)°, V = 1819.5(10) Å3, R1 = 0.081 for 4134 independent observed reflections. Both compounds are isostructural. Their structures are based upon sheets with the chemical composition [(UO2)3(SeO4)5]4−. The sheets are parallel to (0 0 1) and are formed by corner sharing between UO7 pentagonal bipyramids and SeO42− tetrahedra. The [M2+(H2O)6]2+ octahedra (M = Co, Zn) and additional H2O molecules are located between the sheets providing linkage via hydrogen bonding. Topology of the uranyl selenate sheets in the structures of M2[(UO2)3(SeO4)5](H2O)16 (M = Co, Zn) is discussed and its relation to the known topologies of uranyl compounds are considered on the basis of a nodal representation.