Abstract

The crystal structure of elyite, Pb4Cu(SO4)O2(OH)4·H2O, a = 14.233(2), b = 11.532(1), c = 14.611(2) Å, β = 100.45(1)°, V = 2358.4(5) Å3, Z = 8, was solved by direct methods and refined in space group P21/c to R1 = 3.64% and wR2 = 5.10% for the 5861 independent reflections. Data were collected on a tiny untwinned crystal fragment with a four-circle diffractometer (MoKα radiation, CCD area detector). The structure contains eight unique Pb atoms, two isolated Cu atoms in planar fourfold-coordination (<Cu-O> = 1.933, 1.927 Å) and two isolated, almost ideal SO4 tetrahedra. All anions coordinating Cu are OH groups. Two H2O molecules are weakly bound to Pb atoms. The Pb atoms show highly variable coordinations due to variable stereochemical activities of the Pb2+ lone electron pairs. The connectivity of the structure is based on Pb-O polyhedra which are closely linked by common O ligands to form rod-like structure elements parallel to the b axis. The structure frame-work is held together by sharing ligands with CuO4 squares and SO4 tetrahedra. The CuO4 squares can be considered as struts connecting the Pb-O rods along the c axis and, intermittently, along the a axis. A complex hydrogen bond system provides additional strengthening. The non-merohedral twinning parallel to {100} reported previously is explained by the presence of a pseudo-mirror plane in the structure. Comparisons are drawn with the structures of the related Pb-Cu-sulfates chenite, Pb4Cu(SO4)2(OH)6, and linarite, PbCu(SO4)(OH)2. The violet color of elyite and other Cu compounds might be related to the planar fourfold-coordination of Cu.

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