Abstract

The crystal structure of chenevixite, Cu2M2(AsO4)2(OH)4 (where M = Fe3+ or Al), pseudo-orthorhombic, monoclinic, a = 5.7012(8), b = 5.1801(7), c = 29.265(2) Å, β = 89.99(1)°, V = 864.3(4) Å3, space group B1211, Z = 4, was solved by direct methods and refined by least-squares techniques to R = 8.4% and a goodness-of-fit (S) of 1.37 for 1176 unique observed (F⩾4σF) reflections collected for a twinned microcrystal using graphite-monochromated Mo-Kα X-rays and a CCD area detector. Vertex- and edge-sharing arsenate tetrahedra, Alϕ6 octahedra, and Jahn-Teller-distorted Cu2+ϕ6 octahedra [ϕ: O2−, (OH) ] form a framework unique from those in Cu2+ oxysalt minerals. Chains of edge-sharing Cu2+ϕ6 octahedra, with Alϕ6 octahedra attached on opposing sides by the sharing of edges, are linked into layers parallel to (001) by sharing vertices with AsO4 tetrahedra, and the layers are linked to form a framework by the sharing of polyhedral elements between adjacent Alϕ6 octahedra, as well as between AsO4 tetrahedra and Alϕ6 octahedra.

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