Redetermination of brackebuschite, Pb2Mn3+(VO4)2(OH)

Barbara Lafuente, Robert T Downs

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Abstract

The crystal structure of brackebuschite, ideally Pb2Mn3+(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 A2M(T1O4)(T2O4)(OH, H2O), with A = Pb2+, Ba, Ca, Sr; M = Cu2+, Zn, Fe2+, Fe3+, Mn3+, Al; T1 = As5+, P, V5+; and T2 = As5+, P, V5+, S6+. The crystal structure of brackebuschite is based on a cubic closest-packed array of O and Pb atoms with infinite chains of edge-sharing [Mn3+O6] octahedra located about inversion centres and decorated by two unique VO4 tetrahedra (each located on a special position 2e, site symmetry m). One type of VO4 tetrahedra 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 tetrahedra link two adjacent octahedra by sharing two vertices with them and thereby participating in the formation of a three-membered MN2V ring between the central atoms. The 1 ∞[Mn3+(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 ∞[Mn3+(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 hydroxy group bridges one Pb2+ cation with two Mn3+ cations and forms an almost linear hydrogen bond with a vanadate group of a neighbouring chain. The O⋯O distance of this interaction determined from the structure refinement agrees well with Raman spectroscopic data.

Original languageEnglish (US)
Pages (from-to)293-296
Number of pages4
JournalActa Crystallographica Section E: Crystallographic Communications
Volume72
DOIs
Publication statusPublished - 2016

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Keywords

  • brackebuschite
  • crystal structure
  • Raman spectroscopy
  • redetermination

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Materials Science(all)
  • Chemistry(all)

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