Thallous dithionate, Tl₂S₂O₆

Thallous dithionate, Tl₂S₂O₆, is prepared in aqueous solution from barium dithionate and thallous sulphate in equivalent proportions. It crystallises in shining, monoclinic prisms (a:b:c = 0.9292:1:0.3986; β = 96°58') of density 5.573, and one gram of the salt at 18.5° dissolves in 2.39 grams of water.

Potassium dithionate forms trigonal crystals, but with thallous dithionate it gives two series of mixed crystals, so that each salt is probably dimorphous. Thallous dithionate is isomorphous and forms monoclinic mixed crystals with barium dithionate. It also forms a triclinic, double salt with thallous sulphate, 3Tl₂S₂O₆.Tl₂SO₄, and a monoclinic compound with thallous hydroxide, Tl₂S₂O₆.TlOH.H₂O.