The crystal structure of tetra-arsenic trisulphide

Abstract

The crystal structure of synthetic α-dimorphite, As₄S₃, has been determined by a three-dimensional single-crystal X-ray examination. The crystals, of space group Pnma, have Z= 4 in a unit cell of dimensions a= 9·12, b= 7·99, and c= 10·10 Å. The structure was determined by application of Sayre's equation and electron-density methods, and refined anisotropically to R 0·11 for 575 observed reflections. The crystal consists of As₄S₃ molecules, of symmetry C_3v, with four arsenic atoms in a triangular pyramidal arrangement and sulphur bridges along the three adjacent apical edges. Mean As–As and As–S distances are 2·45 and 2·21 Å.