CRYSTAL CHEMISTRY OF MERCURY SULFOHALIDES OF COMPOSITION HG3S2HAL2 (HAL: CL, BR). II. CRYSTAL STRUCTURES OF TWO POLYMORPHIC MODIFICATIONS OF HG3S2BR2-XCLX (X ≈ 0.5)

Abstract

Two polymorphic modifications of Hg2+3 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 ( F0 >4∑F) for compounds I and II, respectively. Compound I is monoclinic, space group C2/m, a 17.824(4), b 9.238(2), c 10.269(2) Å, β 115.69(1)°, V 1523.8(5) Å3, Z = 8. Compound II is cubic, space group Pm3n, a 18.248(2) Å, V 6076.4(1) Å3, Z = 32. In both structures, the Hg atoms are covalently bonded to two S atoms each at 2.366(6)-2.430(5) Å [∠S-Hg-S 163.03(19)-176.3(2)°]. 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)°. In compounds I and II, the SHg3 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.