THE CRYSTAL STRUCTURE OF A POLYMORPH OF Hg2+3S2Br1.0Cl0.5I0.5

Abstract

Grechishchevite, Hg3S2(Br,Cl,1)2, is the only known mercury sulfohalide whose anionic part involves three halogens Cl, Br, and I, in addition to sulfur. The crystal structure of the mineral was not solved. The structure of a synthetic polymorph of Hg2+3S2Br1.0Cl0.5 l0.5 Z = 8, orthorhombic, a 13.249(3), b 13.259(3), c 8.710(2) Å. V 1530.1(5) Å3, space group Pbnm, has been solved by direct methods, and refined to an R of 0.0363 based on 1438 unique reflections (Rint = 0.049) measured with MoKα radiation on a CAD-4 automated diffractometer. The structure contains four independent mercury atoms; each Hg2+ ion is covalently bonded to two sulfur atoms at a diatance of 2.358(4)-2.459(4) Å; the angles S(2)-Hg(2)-S(1) and S(1)'-Hg(4)-S(2) are equal to 172.81(15)° and 172.90(15)°, respectively. It should be noted that the angles S(2)'-Hg(1)-S(2) (141.8(2)'1 and S(1)'-Hg(3)-S(1) [140.9(2)°] greatly deviate from linearity. Each S2- ion is covalently bonded to three mercury atoms at a distance 2.358(4)-2.459(4) Å; the Hg-S-Hg angle ranges from 95.95(14) to 104.91(17)°. These units form the structural motif of the eight-member [Hg4 S4] rings, which are combined into infinite crankshaft-type bands running along [001]. The halogen atoms are located inside and between the crankshaft-type bands, with the Hg-Cl, Hg-Br and Hg-I distances equal to 2.768(6)-2.804(6), 3.040(2)-3.078(2) and 3.259(1)-3.304(1) Å, respectively. Taking into account the halogen atoms, the Hg(1)-Hg(4) atoms have a distorted octahedral coordination. We describe the crystal-chemical peculiarities of the mercury chalcogenide halides, Hg3X2Hal2 (X = S. Se, Te; Hal = F, Cl, Br, I).