Structural Units in Three Uranyl Perrhenates

Three uranyl perrhenates have been synthesized, and their structures have been determined. (UO2)2(ReO4)4(H2O)3 (1) is triclinic, space group P1̄, a = 5.2771(7), b = 13.100(2), c = 15.476(2) Å, α = 107.180(2), β = 99.131(3), γ = 94.114(2)°, V = 1001.12 Å3, Z = 2. [(UO2)4(ReO4)2O(OH)4(H2O)7](H2O)5 (2) is also triclinic, space group P1̄, a = 7.884(1), b = 11.443(2), c = 16.976(2) Å, α = 83.195(4), β = 89.387(4), γ = 85.289(4)°, V = 1515.70 Å3, Z = 2. Na(UO2)(ReO4)3(H2O)2 (3) is monoclinic, space group C2/m, a = 12.311(3), b = 22.651(6), c = 5.490(1) Å, β = 109.366(6)°, V = 1444.24 Å3, Z = 4. These compounds are the first structurally characterized uranyl perrhenates that do not contain organic ligands. In each structure, perrhenate groups coordinate uranyl ions at the equatorial vertices of pentagonal bipyramids. 1 contains complex chains of uranyl pentagonal bipyramids that are bridged by vertex sharing with perrhenate groups. The structural units in 2 and 3 consist of three novel finite clusters that include the coordination of uranyl ions with perrhenate. In general, weakly coordinating ligands such as perchlorate, perrhenate, and pertechnetate are assumed not to form stable complexes with uranyl in solutions or solids. The current findings, together with other recently reported studies, indicate each of these ligands can coordinate uranyl, and novel structure types result.