TL3AL7S12 - A NOVEL AL-RICH THIOALUMINATE - PREPARATION, CRYSTAL-STRUCTURE, AND PROPERTIES

The new ternary phase Tl3Al7S12 was prepared from the binary compounds Tl2S and Al2S3 at 700-degrees-C under vacuum. The structure of a yellow plateshaped single crystal was determined at room temperature. The compound crystallizes in the monoclinic polar space group P2(1) (No. 4) with a = 9.040(2), b = 12.381(2), c = 9.569(2) angstrom and beta = 95.91(2)-degrees. The polymeric anionic part of the structure can be described as a puckered layer-like arrangement of corner-sharing [AlS4]-tetrahedra parallel to (001). The aluminium-sulfur layers are connected via single sulfur atoms. The voluminous monovalent thallium atoms bridge the layers of the anionic framework. The mean Al-S bond lengths are 2.227 angstrom for mu2-S-Al and 2.298 angstrom for mu3-S-Al. In the strongly asymmetric coordination sphere of thallium the Tl-S bond lengths vary from 3.009(9) to 3.907(9) angstrom and contain four short and two or three longer distances. A rather short Tl...Tl distance of 3.619(3) angstrom is observed between two of the three crystallographically independent Tl atoms, so that a weak bonding interaction has to be discussed. Vibrational spectroscopic data for the new phase are reported and discussed.