Single-crystal structure determination of perroudite, Hg5Ag4S5(I, Br)2Cl2, from Tsumeb (Namibia), and its structural relationships to other sulfide halides of mercury and cinnabar
Keller, Paul; Lissner, Falk; Schleid, Thomas
published: Jan 21, 2005
ArtNo. ESP154018101001, Price: 29.00 €
The crystal structure of perroudite, Hg5Ag4S5(I, Br)2Cl2, orthorhombic, P21212 (No. 18), a = 17.4198(9), b = 12.2032(6) and c = 4.2088(2) Å, Z = 2, has been determined by using a single crystal from Tsumeb, Namibia. The refinement of 1761 unique reflections converged to R1 = 5.21%. The results of a previous structure determination on a "fused bundle of several small crystals" have been significantly improved: (i) The structural formula is Hg5Ag4S5(I, Br)2Cl2 without any coupled substitution, (ii) Cl and I occupy individual sites and (iii) only I is replaced by significant amounts of Br. Three symmetrically distinct Hg2+ form distorted octahedra with two short bonds HgS = 2.346 2.372 Å and four longer bonds: HgS = 3.088 3.364 Å, HgCl = 3.114 3.338 Å, and Hg(I, Br) = 3.421 3.436 Å. Two unique Ag + are four-coordinated in a strongly distorted tetrahedral arrangement. Their bond lengths are: AgS = 2.519 2.685 Å, AgCl = 2.549, and Ag(I, Br) = 2.661 3.035 Å. Typical features of the structure are (i) helical HgS chains, similar to those of cinnabar (HgS), but different from any other Hg sulfide halide and (ii) face sharing Hg2+ octahedra that form [Hg(1)Hg(2)2S4Cl2(I, Br)2]6 triple chains topologically comparable with a fragment of the NiAs structure type. They are further linked by [Hg(3)2S3Cl2(I, Br)2]6 double chains to a framework structure with open channels along . These are occupied by the Ag+ cations and their linkages. Structural relationships with capgaronnite, corderoite, cinnabar and the chemical compounds HgCuSCl, βHg3S2Br2 and Hg3S2I3 are discussed on the basis of crankshaft and zigzag HgS chains as well as face-sharing octahedra as fundamental building units.