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An x-ray crystallographic study of the crystal structures of four tellurium oxysalt minerals : dugganite, choloalite, rodalquilarite, and graemite

University of British Columbia

The crystal structures of four tellurium oxysalt minerals, dugganite, choloalite, rodalquilarite, and graemite, were investigated with the use of single crystal X-ray crystallography. The crystal structure of dugganite, ideally Pb₃Zn₃Te⁶⁺As₂O₁₄, a 8.460(2), c 5.206(2) Å, V 322.6(2) ų, space group P321, Z 1, has been solved by direct methods and Patterson techniques, and refined to an R index of 2.7% based on 636 unique reflections measured using MoKα radiation on an automated four-circle diffractometer. The structure consists of heteropolyhedral sheets of edge-sharing TeO₆ octahedra and PbO₈ snub disphenoids, oriented parallel to (001). The sheets are cross-linked by AsO₄ and ZnO₄ tetrahedra, which share corners to form an interlinked, two- and three-connected two-dimensional net parallel to (001). Cheremnykhite and kuksite are considered to be isostructural with dugganite, but with V and P respectively dominant at the As site. The crystal structure of choloalite, ideally Cu₃Pb₃Te⁴⁺₆O₁₈(Cl,H₂O), α 12.520(4) Å, V 1963(2) ų, space group P4₁32, Z4, has been solved by direct methods and Patterson techniques, and refined to an R index of 5.2% based on 956 unique reflections measured using MoKα radiation on an automated four-circle diffractometer. The structure consists of distorted TeO₆ octahedra, CuΦ₅ square pyramids (where Φ = CI and H₂O), Pb(1)O₉ triaugmented trigonal prisms, and Pb(2)O₁₂ icosahedra. The Pb(1)O₉ polyhedra polymerize to form a threedimensional network, as do the CuΦ₅ and Pb(2)O₁₂ polyhedra. The two networks fit together in three-dimensional space, leaving voids which are filled by the TeO₆ octahedra. The crystal structure of rodalquilarite was originally solved, using photographic methods, to an R index of 9.2%by Dusausoy and Protas (1969). Rodalquilarite, ideally H₃Fe₂(TeO₃)₄Cl, a 9.021(1) b 5.1170(7), c 6.6539(8) Å, α 103.23(1)°, β 106.66(1)°, γ 78.07(1)°, V 283.15(6) ų, space group P1, Z1 was redetermined and refined to an R index of 4.1% based on 1672 unique reflections measured using MoKα radiation on an automated four-circle diffractometer. The structure consists of chains of FeO₆ octahedra parallel to the b-axis connected with tellurium polyhedra to form planes parallel to be. These planes are held together by hydrogen and long (>3.0 Å) Te-Φ) (where Φ = O or CI) bonds. A four-circle diffractometer equipped with synchrotron radiation was used to collect a data set for graemite, CuTeO₆H₂0. Data yielded a 6.816, b 25.627, c 5.784, with all angles 90°. Structural models were refined to an R index of 6.9% in Pmc2₁ and to 7.7% in a reduced cell (1/2 a) using Pna2₁ . Neither of the models gave a satisfactory result although a substructure in Pna2₁ is proposed. Precession photographs show the presence of disorder in the structure. Further study, including upper level precession work and electron microprobe analysis, is required.

Thesis/Dissertation

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2009-05-26

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http://hdl.handle.net/2429/8180

Environmental Sciences

University of British Columbia

UBCV

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