Synthesis and Characterization of Heavier Dioxouranium(VI) Dihalides^†

The synthesis and characterization of the dioxouranium(VI) dibromide and iodide hydrates, UO2Br2·3H2O (1), [UO2Br2(OH2)2]2 (2), and UO2I2·2H2O·4Et2O (3), are reported. Moreover, adducts of UO2I2 and UO2Br2 with large, bulky OP(NMe2)3 and OPPh3 ligands such as UO2I2(OP(NMe2)3)2 (4), UO2Br2(OP(NMe2)3)2 (5), and UO2I2(OPPh3)2 (6) are discussed. The structures of the following compounds were determined using single-crystal X-ray diffraction techniques: (1) monoclinic, P21/c, a = 9.7376(8) Å, b = 6.5471(5) Å, c = 12.817(1) Å, β = 94.104(1)°, V = 815.0(1) Å3, Z = 4; (2) monoclinic, P21/c, a = 6.0568(7) Å, b = 10.5117(9) Å, c = 10.362(1) Å, β = 99.62(1)°, V = 650.5(1) Å3, Z = 2; (4) tetragonal, P41212, a = 10.6519(3) Å, b = 10.6519(3) Å, c = 24.0758(6) Å, V = 2731.7(1) Å3, Z = 4; (5) tetragonal, P41212, a = 10.4645(1) Å, b = 10.4645(1) Å, c = 23.7805(3) Å, V = 2604.10(5) Å3, Z = 4, and (6) monoclinic, P21/c, a = 9.6543(1) Å, b = 18.8968(3) Å, c = 10.9042(2) Å, β = 115.2134(5)°, V = 1783.01(5) Å3, Z = 2. Whereas 1 and 2 are the first UO2Br2 hydrates and the last missing members of the UO2X2 hydrate (X = Cl → I) series to be structurally characterized, 4 and 6 contain room-temperature stable UVI−I bonds with 4 being the first structurally characterized room temperature stable UVI−I compound which can be conveniently prepared on a gram scale in quantitative yield. The synthesis and characterization of 5 using an analogous halogen exchange reaction to that used for the preparation of 4 is also reported.