CRYSTAL STRUCTURES OF SYNTHETIC GOLD-BEARING SULFOSALTS

Abstract

Hydrothermal syntheses in sealed gold tubes produced four distinct sulfosalts of Pb-Bi-Sb-Au, three of them suitable for crystal structure analysis. They have distinct linear-coordinated Au + sites in the structure. The crystal structure of Au 2 Pb 20 (Sb,Bi) 16 S 45 is composed of two types of rods based on SnS archetype, with Pb atoms on the outer surfaces and predominantly Sb and Bi sites in the rod interior. Lead also occurs in the central portions of the larger rod. Linear-coordinated Au and an additional (Pb,Bi) site are interstitial to the rods. The crystal structure of Au 2 Pb 20 (Sb,Bi) 16 S 45 is orthorhombic, space group Cmc 2 1 , with lattice parameters a 4.0260(2), b 75.207(7), and c 27.525(1) A, and unit cell volume 8334.3 A 3 . Two structures, Au 2 Pb 12 (Bi,Sb) 18 S 40 and Au 2 Pb 22 (Bi,Sb) 18 S 50 , are homologues N = 2 and N = 4, of a structural series in which slabs of lillianite structure alternate with wavy (100) PbS layers of incrementally increasing thickness (2 and 4 atomic sheets thick, respectively). Linear-coordinated gold (Au-S distance from 2.20 to 2.46 A) occurs in the former slabs at the boundary to the latter ones. Unit-cell parameters of Au 2 Pb 12 Sb 18 S 40 are as follows: a 4.11(1), b 44.50(1), and c 20.56(1) A (film data), cell volume 3760.3 A 3 , and space group Cmc 2 1 . Those of Au 2 Pb 22 Sb 18 S 50 are a 4.0876(4), b 55.1514(48), and c 20.4219(11) A, cell volume 4604.29 A 3 , and the same space group. The increment of the b parameter reflects the change in the homologue number N.