Crystal chemistry of mercury sulfohalides of composition Hg3S2Hal2 (Hal: Cl, Br).: II.: Crystal structures of two polymorphic modifications of Hg3S2Br2-xClx (x ≈ 0.5)

Two polymorphic modifications of Hg32+S2Br1.5Cl0.5 (I, II) have been prepared in attempts to obtain a synthetic analogue of arzakite, Hg3S2(Br,Cl)(2) (Br >= Cl), a rare supergene sulfohalide mineral of mercury. The structures of the two phases were solved by direct methods and refined to an R of 0.0513 and 0.0380 using 1539 and 1006 unique observed reflections (vertical bar F-o vertical bar > 4 sigma(F)) for compounds I and 11, respectively. Compound I is monoclinic, space group C2/m, a 17.824(4), b 9.238(2), c 10.269(2) angstrom, beta 115.69(1)degrees, V 1523.8(5) angstrom(3), Z = 8. Compound II is cubic, space group Pm (3) over barn, a 18.248(2) angstrom, V 6076.4(1) angstrom(3), Z = 32. In both structures, the Hg atoms are covalently bonded to two S atoms each at 2.366(6)-2. 430(5) angstrom[< S-Hg-S 163.03(19)-176.3(2)degrees]. Each S atom is bonded to three mercury atoms to form SHg3 trigonal pyramids with the Hg-S-Hg angles in the range 95.66(19)-97.60(20)degrees. In compounds I and II, the SHg9 fragments share the Hg vertices to form isolated cubes with S atoms at the corner and Hg atoms in the middle of the edges. Halogen atoms are located both within and in between the [Hg12S8] cubes. As in other mercury chalcohalide structures, the halogen atoms determine the structural architecture of the compounds, as they form the cubic sublattices that accommodate the Hg-S units. Taking into account the halogen atoms, the Hg atoms are in distorted octahedral coordination.