Tl 2S: Re-Determination of Crystal Structure and Stereochemical Discussion

Abstract

The crystal structure of synthetic carlinite, Tl 2S, was re-determined by single crystal and powder X-ray diffraction methods. The cell parameters obtained from Rietveld refinement are a=12.150(2) Å, c=18.190(4) Å, V=2325.5(7) Å 3. A single crystal data refinement proved Tl 2S crystallizing in the trigonal space group R3 with M=440.8gmol −1, Z=27, R=0.076, and w R=0.145. The atomic arrangement found is that of a strongly deformed anti-CdI 2 type, but the deformation is clearly different from that given by previous workers. In the five crystallographically different STl 6 octahedra the S–Tl distances vary between 2.82 and 3.09Å, the Tl–Tl edges between 3.52 and 4.58Å. The common features of these octahedra are (i) each one with a definitely smaller vs larger Tl 3 face in trans-position, both faces parallel or sub-parallel (00.1), and (ii) each three shorter and longer S–Tl distances to the atoms of the larger and smaller Tl 3 faces, respectively. The Tl–Tl contacts between different Tl 2S sheets are on the average definitely shorter than the ones within the sheet and they can be smaller than the Tl–Tl contacts in the small Tl 3 faces of the STl 6 octahedra. The atomic arrangement indicates that the single electron pairs of the monovalent Tl atoms are not arranged all parallel to the z-axis, as one would expect for Tl 2S with an ideal anti-CdI 2 structure. The surrounding of the S atoms resembles that of one-third of the Cl atoms in yellow InCl. The absorbance of Tl 2S is very low at wave numbers approximately <9000 cm −1.