A new uranyl phosphate chain in the structure of parsonsite

The structure of parsonsite, Pb 2 [(UO 2 )(PO 4 ) 2 ], Z= 2, triclinic, space group P1̅, a = 6.842(4), b = 10.383(6), c = 6.670(4) Å, α = 101.26(7)°, (β = 98.17(7)°, γ = 86.38(7)°, V= 459.8(7) Å 3 , has been solved by direct methods and refined to R = 6.0 and a goodness-of-fit (5) of 0.92 using 1187 unique observed reflections (|F|≥4σ F ) collected with MoKα X-rays and a CCD-based detector. The single unique U 6+ cation is present as a (UO 2 ) 2+ uranyl ion (Ur) and is coordinated by five additional atoms of O arranged at the equatorial corners of a pentagonal bipyramid capped by the O Ur atoms. Uranyl polyhedra share an edge-forming dimers, wh|ich are cross-linked by edge- and vertex-sharing with two distinct phosphate tetrahedra, resulting in a new uranyl phosphate chain. Two symmetrically distinct Pb 2+ cations are coordinated by nine and six oxygen atoms, and link adjacent uranyl phos­phate chains. Parsonsite is the first uranyl phosphate mineral structure that is based upon chains of polymerized polyhedra of higher bond-valence; others contain sheets that are either based upon the autunite or phosphuranylite anion-topologies.