Acta Cryst. (2001). E57, i115-i118  [ doi:10.1107/S1600536801020050 ]

Redetermination of the mixed-valence manganese arsenate flinkite, Mn^II₂Mn^III(OH)₄(AsO₄)

U. Kolitsch

Abstract: The crystal structure of the rare mixed-valence manganese(II,III) arsenate mineral flinkite [dimanganese(II) manganese(III) arsenate tetrahydroxide], Mn^II₂Mn^III(OH)₄(AsO₄) has been redetermined from single-crystal X-ray data. The previously unknown positions of both H atoms could be identified. Flinkite contains one unique Mn^IIIO₂(OH)₄ polyhedron with a Jahn-Teller-distorted [4+2]-coordination of Mn^III, one Mn^IIO₃(OH)₃ octahedron, and one fairly regular AsO₄ tetrahedron. Atoms on special sites are Mn1 (site symmetry ), As, O4 and O5 (all with site symmetry  .m.). The structure is based upon pyrochroite [Mn(OH)₂]-type sheets of edge-sharing Mn(O,OH)₆ octahedra parallel to (100). Some Mn(O,OH)₆ octahedra are omitted to allow AsO₄ tetrahedra to connect the sheets via shared corners. Additional strong hydrogen bonds between the sheets provide further strengthening. Relations to the structures of antlerite, Cu₃(SO₄)(OH)₄, synthetic Cu₃(SeO₄)(OH)₄, synthetic Cu₃(CrO₄)(OH)₄, and szenicsite, Cu₃(MoO₄)(OH)₄, are pointed out.

Online 30 November 2001

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