Thallium sesquibromide, Tl₂Br₃

Thallium sesquibromide, Tl₂Br₃ or 3TlBr.TlBr₃, is not so readily prepared as the corresponding chloride, since it is decomposed by water. The best method of preparation is to moisten 4 or 5 grams of thallous bromide with 1 or 2 c.c. of water and slowly add 0.5 c.c. of bromine. About 50 grams of water are then added, and the liquid brought to the boiling-point. The slight residue of thallous bromide is filtered off, and the filtrate caught in a vessel that is cooled by immersion in running water. Thallium sesquibromide separates out in bright red crystals. Water decomposes the bromide into thallic bromide and a solid the composition of which depends upon the relative amounts of sesquibromide and water, but which is intermediate between that of the sesquibromide and thallous bromide. Thallium sesquibromide forms orange-yellow or orange-red mixed crystals with thallous bromide.