• journal_title：The Canadian Mineralogist
• Contributor：Andrew J. Locock ; Peter C. Burns ; Theodore M. Flynn
• Publisher：Mineralogical Association of Canada
• Date：2005-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.43.2.721
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：43
• issue：2
• firstpage：721
• section：Articles

Strontium and barium uranyl phosphate and uranyl arsenate hydrates have been synthesized by diffusion in gels (SrUP11, Sr[(UO₂)(PO₄)]₂(H₂O)₁₁, SrUAs11, Sr[(UO₂)(AsO₄)]₂(H₂O)₁₁, synthetic heinrichite, Ba[(UO₂)(AsO₄)]₂(H₂O)₁₀), or by hydrothermal methods (synthetic meta-uranocircite I, Ba[(UO₂)(PO₄)]₂(H₂O)₇), and their crystal structures have been determined. Single-crystal X-ray-diffraction intensity data were collected at room temperature using MoKα radiation and a CCD-based area detector. The crystal structures of the four compounds were solved by direct methods and refined by full-matrix least-squares techniques on the basis of F² for all unique reflections to agreement indices (SrUP11, SrUAs11, synthetic heinrichite and synthetic meta-uranocircite I) R1 of 3.6, 5.2, 4.3 and 5.2%, respectively. These compounds contain the autunite-type sheet of composition [(UO₂)(XO₄)]⁻, X = P or As, which involves the sharing of equatorial vertices of uranyl square bipyramids with tetrahedra. The interlayer region contains cations and H₂O groups, and the sheets are linked by hydrogen bonding and through bonds from the interlayer cations to oxygen atoms of the sheets. SrUP11 is orthorhombic, space group Pnma, a 14.042(6), b 21.008(9), c 6.997(3) Å, V 2064.1(15) ų, Z = 4, D_calc 3.269 g/mL. SrUAs11 is orthorhombic, space group Pnma, a 14.3778(6), b 20.9611(9), c 7.1703(3) Å, V 2160.95(16) ų, Z = 4, D_calc 3.392 g/mL. These Sr compounds are isostructural with autunite, Ca[(UO₂)(PO₄)]₂(H₂O)₁₁. On this basis, uranospinite is predicted to be isostructural with autunite, and have the formula Ca[(UO₂)(AsO₄)]₂(H₂O)₁₁, with expected crystal-data: orthorhombic, space group Pnma, a 14.35, b 20.66, c 7.17 Å, V 2125 ų, Z = 4, D_calc 3.3 g/mL. Synthetic heinrichite is monoclinic, space group P2/c, a 7.1548(11), b 7.1340(11), c 21.290(3) Å, β 104.171(5)°, V 1053.6(3) ų, Z = 2, D_calc 3.579 g/mL. The unit cell of synthetic uranocircite, Ba[(UO₂)(PO₄)]₂(H₂O)₁₀, was measured from a crystal aggregate, but a structure refinement is not presented. Synthetic uranocircite is interpreted to be isostructural with heinrichite: monoclinic, space group P2/c, a 7.01, b 6.99, c 21.2 Å, β 103.9°, V 1008.4 ų, Z = 2, D_calc 3.45 g/ mL. The structure of synthetic meta-uranocircite I was determined from a crystal twinned by pseudomerohedry, and is monoclinic, space group P2₁, a 6.943(2), b 17.634(6), c 6.952(2) Å, β 90.023(7)°, V 851.2(5) ų, Z = 2, D_calc 3.876 g/mL. Metaheinrichite is predicted to be isostructural with synthetic meta-uranocircite I, with the formula Ba[(UO₂)(AsO₄)]₂(H₂O)₇, and expected crystal-data: monoclinic, space group P2₁, a 7.08, b 17.7, c 7.09 Å, β 90.02°, V 889 ų, Z = 2, D_calc 4.0 g/mL.