A new uranyl phosphate chain in the structure of parsonsite

The structure of parsonsite, Pb-2[(UO2)(PO4)(2)], Z= 2, triclinic, space group P (1) over bar, a = 6.842(4), b = 10.383(6), c = 6.670(4) Angstrom, alpha = 101.26(7)degrees, beta = 98.17(7)degrees, gamma = 86.38(7)degrees, V= 459.8(7) Angstrom(3), has been solved by direct methods and refined to R = 6.0 and a goodness-of-fit (S) of 0.92 using 1187 unique observed reflections (\ F \ greater than or equal to 4 sigma(F)) collected with MoK alpha X-rays and a CCD-based detector. The single unique U6+ cation is present as a (UO2)(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, which are cross-linked by edge- and vertex-sharing with two distinct phosphate tetrahedra, resulting in a new uranyl phosphate chain. Two symmetrically distinct Pb2+ 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.