Thallous fluoride, TlF

Thallous fluoride, TlF, is prepared by dissolving thallous hydroxide, carbonate, or sulphide in aqueous hydrofluoric acid, evaporating to dryness, heating to remove hydrogen fluoride, and crystallising the residue from water. It may also be prepared by heating thallous oxide or carbonate to dull redness in a stream of dry hydrogen fluoride. Thallium dissolves slowly in aqueous hydrofluoric acid.

Thallous fluoride is readily soluble in water, from which it crystallises in colourless, lustrous, regular octahedra. At a red heat it may be distilled in a current of hydrogen fluoride. It is insoluble in alcohol and in liquid ammonia; the aqueous solution has an acid reaction.

The monohydrate, TlF.H₂O, is said to separate in monoclinic crystals from a solution of thallous carbonate in aqueous hydrofluoric acid; and thallium hydrogen fluoride, TlF.HF, crystallises out in regular octahedra when a solution of thallous fluoride in concentrated aqueous hydrofluoric acid is evaporated over sulphuric acid. The acid fluoride is stable at 100°, but decomposes at higher temperatures (Buchner).

Aluminium thallous fluoride, 2AlF₃.3TlF, and numerous other double fluorides have been prepared.