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Redetermination of conichalcite, CaCu(AsO(4))(OH).

ABSTRACT: The crystal structure of conichalcite [calcium copper(II) arsenate(V) hydroxide], with ideal formula CaCu(AsO(4))(OH), was redetermined from a natural twinned specimen found in the Maria Catalina mine (Chile). In contrast to the previous refinement from photographic data [Qurashi & Barnes (1963 ?). Can. Mineral. 7, 561-577], all atoms were refined with anisotropic displacement parameters and with the H atom located. Conichalcite belongs to the adelite mineral group. The Jahn-Teller-distorted [CuO(6)] octa-hedra share edges, forming chains running parallel to [010]. These chains are cross-linked by eight-coordinate Ca atoms and by sharing vertices with isolated AsO(4) tetra-hedra. Of five calcium arsenate minerals in the adelite group, the [MO(6)] (M = Cu, Zn, Co, Ni and Mg) octa-hedron in conichalcite is the most distorted, and the donor-acceptor O-H?O distance is the shortest.

SUBMITTER: Henderson RR

PROVIDER: S-EPMC2960568 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Redetermination of conichalcite, CaCu(AsO(4))(OH).

Henderson Rachel R RR Yang Hexiong H Downs Robert T RT Jenkins Robert A RA

Acta crystallographica. Section E, Structure reports online 20080806 Pt 9

The crystal structure of conichalcite [calcium copper(II) arsenate(V) hydroxide], with ideal formula CaCu(AsO(4))(OH), was redetermined from a natural twinned specimen found in the Maria Catalina mine (Chile). In contrast to the previous refinement from photographic data [Qurashi & Barnes (1963 ▶). Can. Mineral. 7, 561-577], all atoms were refined with anisotropic displacement parameters and with the H atom located. Conichalcite belongs to the adelite mineral group. The Jahn-Teller-distorted [Cu ...[more]

PMID: 21201563

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Project description:The crystal structure of brackebuschite, ideally Pb2Mn(3+)(VO4)2(OH) [dilead(II) manganese(III) vanadate(V) hydroxide], was redetermined based on single-crystal X-ray diffraction data of a natural sample from the type locality Sierra de Cordoba, Argentina. Improving on previous results, anisotropic displacement parameters for all non-H atoms were refined and the H atom located, obtaining a significant improvement of accuracy and an unambiguous hydrogen-bonding scheme. Brackebuschite belongs to the brackebuschite group of minerals with general formula A 2 M(T1O4)(T2O4)(OH, H2O), with A = Pb(2+), Ba, Ca, Sr; M = Cu(2+), Zn, Fe(2+), Fe(3+), Mn(3+), Al; T1 = As(5+), P, V(5+); and T2 = As(5+), P, V(5+), S(6+). The crystal structure of brackebuschite is based on a cubic closest-packed array of O and Pb atoms with infinite chains of edge-sharing [Mn(3+)O6] octa-hedra located about inversion centres and decorated by two unique VO4 tetra-hedra (each located on a special position 2e, site symmetry m). One type of VO4 tetra-hedra is linked with the (1) ?[MnO4/2O2/1] chain by one common vertex, alternating with H atoms along the chain, while the other type of VO4 tetra-hedra link two adjacent octa-hedra by sharing two vertices with them and thereby participating in the formation of a three-membered Mn2V ring between the central atoms. The (1) ?[Mn(3+)(VO4)2OH] chains run parallel to [010] and are held together by two types of irregular [PbO x ] polyhedra (x = 8, 11), both located on special position 2e (site symmetry m). The magnitude of the libration component of the O atoms of the (1) ?[Mn(3+)(VO4)2OH] chain increases linearly with the distance from the centerline of the chain, indicating a significant twisting to and fro of the chain along [010]. The hy-droxy group bridges one Pb(2+) cation with two Mn(3+) cations and forms an almost linear hydrogen bond with a vanadate group of a neighbouring chain. The O?O distance of this inter-action determined from the structure refinement agrees well with Raman spectroscopic data.

Dataset Information

Redetermination of conichalcite, CaCu(AsO(4))(OH).

Publications

Redetermination of conichalcite, CaCu(AsO(4))(OH).

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