Layer-chain Structures of Thallium Di-Alkyl Halides

Abstract

DURING the last year we have been studying the crystal structures of a series of compounds R₂TIX, which prove to be of some interest in view of the recent work on the rotation of molecules in crystals. The dimethyl thallium halides are tetragonal and the others orthorhombic, pseudo-tetragonal, and all show a sodium chloride-like structure. Layers of TIX parallel to the ab plane are spaced out at distances depending on the length of the alkyl chains, which are attached to the thallium ions perpendicularly to these layers. The a and b cell dimensions are almost independent of the alkyl group and vary between 4.29 A. (chloride) and 4.76 A. (iodide). These spacings which, except in the case of the iodide, are much lower than the values 4.85 A. (Müller)¹ and 4.76 A. (Bernal)² found for the distance between rotating chains, are in agreement with other indications that the chains in these compounds do not rotate.