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.