• journal_title：The Canadian Mineralogist
• Contributor：Andrew J. Locock ; Peter C. Burns ; Theodore M. Flynn
• Publisher：Mineralogical Association of Canada
• Date：2004-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.42.6.1699
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：42
• issue：6
• firstpage：1699
• section：Articles

Compounds that contain the autunite-type sheet and divalent cations (Mg, Mn, Fe, Co, Ni) in their interlayers have been synthesized by diffusion in gels or by hydrothermal methods, and their crystal structure determined. Data on single-crystal X-ray-diffraction intensities were collected at room temperature using MoKα radiation and a CCD-based area detector. The autunite-type sheet has the composition [(UO₂)(XO₄)]⁻, X = P or As, and involves the sharing of equatorial vertices of uranyl square bipyramids with phosphate or arsenate tetrahedra. The interlayer region contains H₂O groups and cations in octahedral coordination. The sheets are linked by hydrogen bonding and through bonds from the interlayer cations to oxygen atoms of the sheets. The structural roles of the interlayer cations in determining the symmetries and hydration states observed are discussed. Three different hydration states are observed, and these have characteristic symmetries and basal d-values: dodecahydrates are triclinic (pseudomonoclinic), basal spacing ~11 Å; decahydrates are monoclinic (pseudo-orthorhombic and commonly twinned), basal spacings ~10 Å, and octahydrates are triclinic, basal spacings of ~8.7 Å. Each hydration state corresponds to a different structure-type; the H₂O of hydration of these compounds does not vary in the same fashion as the H₂O content of zeolites, but rather is required to maintain the integrity of the hydrogen-bonding network. Changes in hydration state, whether through dehydration or rehydration, give rise to separate structures. Crystallographic data: Mn[(UO₂)(AsO₄)]₂(H₂O)₁₂: triclinic P1̅, a 7.1359(11), b 7.1439(11), c 11.3616(17) Å, α 81.592(3)°, β 81.639(3)°, γ 88.918(3)°, R1 = 3.3%; Co[(UO₂)(AsO₄)]₂(H₂O)₁₂ (i.e., synthetic “kirchheimerite”): triclinic P1̅, a 7.1552(5), b 7.1586(5), c 11.2912(8) Å, α 81.487(2)°, β 81.410(2)°, γ 88.891(2)°, R1 = 5.1%; Mg[(UO₂)(AsO₄)]₂(H₂O)₁₂ (i.e., synthetic nováčekite I): triclinic P1̅, a 7.1594(5), b 7.1610(5), c 11.3146(7) Å, α 81.391(2)°, β81.177(1)°, γ 88.884(1)°, R1 = 4.3%; Ni[(UO₂)(AsO₄)]₂(H₂O)₁₂: triclinic P1̅, a 7.1523(3), b 7.1583(3), c 11.2564(5) Å, α81.549(1)°, β 81.356(1)°, γ 88.916(1)°, R1 = 2.7%; Ni[(UO₂)(PO₄)]₂(H₂O)₁₂: triclinic P1̅, a 6.9962(15), b 7.0012(15), c 11.171(2) Å, α 81.591(4)°, β 82.189(4)°, γ 88.721(4)°, R1 = 3.2%; Mn[(UO₂)(PO₄)]₂(H₂O)₁₀: monoclinic I2/m, a 6.9656(4), b 20.3768(13), c 6.9775(4) Å, β 91.019(1)°, R1 = 2.7%; Co[(UO₂)(PO₄)]₂(H₂O)₁₀: monoclinic P2₁/n, a 6.9490(5), b 19.9348(16), c 6.9620(5) Å, β 90.440(2)°, R1 = 5.1%; Ni[(UO₂)(PO₄)]₂(H₂O)₁₀: monoclinic P2₁/n, a 6.9506(4), b 19.8215(11), c 6.9711(4) Å, β 90.418(1)°, R1 = 3.1%; Mg[(UO₂)(AsO₄)]₂(H₂O)₁₀ (i.e., synthetic nováčekite II): monoclinic P2₁/n, a 7.1328(11), b 20.085(3), c 7.1569(11) Å, β 90.585(3)°, R1 = 8.5%; Mn[(UO₂)(AsO₄)]₂(H₂O)₈: triclinic P1̅, a 7.2244(5), b 9.9170(8), c 13.337(1) Å, α 75.012(2)°, β84.136(2)°, γ 81.995(2)°, R1 = 2.8%; Fe[(UO₂)(AsO₄)]₂(H₂O)₈ (i.e., synthetic metakahlerite): triclinic P1̅, a 7.2072(3), b 9.8242(4), c 13.2708(6) Å, α 75.370(1)°, β 84.024(1)°, γ 81.839(1)°, R1 = 2.9%; Co[(UO₂)(AsO₄)]₂(H₂O)₈ (i.e., synthetic metakirchheimerite): triclinic P1̅, a 7.1955(3), b 9.7715(4), c 13.2319(6) Å, α 75.525(1)°, β 84.052(1)°, γ 81.661(1)°, R1 = 2.5%.