Crystal data for uranium phosphorus pentoxide, UPO₅, and uranium arsenic pentoxide, UAsO₅

Guinier powder patterns [λ(Cu Kα₁) = 1.5406 Å] of UPO₅ and UAsO₅ have been indexed. UPO₅ is triclinic. The cell dimensions are: a = 5.472(2), b = 5.646(2), c = 7.027(1) Å, α = 87.39(2), β = 93.39(2), γ = 106.51(1)°, V = 207.7 ų, Z = 2, D_x = 5.58 g cm⁻³. The new compound UAsO₅ appears monoclinic. The unit cell has dimensions: a = 8.833(2), b = 6.858(1), c = 7.151(1) Å, β = 96.88(1)°, V = 430.1 ų, Z = 4, D_x = 6.07 g cm⁻³. The space group is P2₁/c. The data show the presence of a strong triclinic C subcell: a = 5.591(1), b = 5.591(1), c = 7.151(1) Å, α = 84.57(1), β = 95.43(1), γ = 104.35(1)°, which suggests that both compounds are structurally related. The JCPDS Diffraction File No. for UPO₅ is 37-1462 and for UAsO₅ 37-1461.