Thallium sesqui-chloride, Tl₂Cl₃

Thallium sesqui-chloride, Tl₂Cl₃ or 3TlCl.TlCl₃, is readily prepared by saturating a boiling solution of thallic chloride with thallous chloride and cooling, or by passing chlorine into water containing thallous chloride in suspension until no more white thallous chloride is left. In each case the product should be recrystallised from boiling water, and in the latter case the too prolonged action of chlorine should be avoided, since it converts the sparingly soluble thallium sesquichloride into very soluble thallic chloride.

Thallium sesquichloride crystallises in yellow, six-sided leaflets, of density 5.9. One litre of water at 25° dissolves 3.43 grams of the chloride. The aqueous solution gives with alkali hydroxides a precipitate of thallic hydroxide, and the filtrate contains thallous salt in solution.

Thallium sesquichloride forms mixed crystals with thallous chloride, on account of which a number of other chlorides have erroneously been described by Werther.