Double Thallic Halide Salts

Double Salts containing Thallic Chloride, Bromide, or Iodide. - A very large number of these double salts is known.

The salts of the type TlX₃.MX.xH₂O appear to possess cubic symmetry, since Pratt and Wallace have shown that the asterisked salts crystallise in combinations of the cube and regular octahedron. Rammelsberg described the potassium salts of the type 2TlX₃.3MX.xH₂O as cubic, but according to Wallace the bromide is tetragonal (a:c = 1:0.7556) and the caesium cliloride is described by Pratt as hexagonal (a:c = 1:0.8257).

Two salts of the type TlX₃.2MX.H₂O crystallise in rhombic bipyramids, isomorphous with the corresponding indium salts and with ammonium and potassium ferric chlorides, FeCl₃.2NH₄Cl.H₂O and FeCl₃.2KCl.H₂O. The data given below are due to Wallace: -

TlCl₃.2RbCl.H₂O; a:b:c = 0.9770:1:1.4388; density = 3.513 at 20°
TlCl₃.2CsCl.H₂O; a:b:c = 0.9690:1:3.4321; density = 3.879 at 20°

The following salts of the type TlX₃.3MX.2H₂O crystallise in tetragonal bipyramids isomorphous with the corresponding indium salts: -

TlCl₃.3KCl.2H₂O; a:c = 1:0.7941; density = 2.859 at 20°
TlCl₃.3NH₄Cl.2H₂O; a:c = 1:0.8097; density = 2.389 at 20°.
TlBr₃.3RbBr.2H₂O; a:c = 1:0.8038; density = 4.077 at 20°

Thallic chloride combines with the chlorides of calcium, strontium, magnesium, zinc, copper, and manganese, forming double salts of the type 2TlCl₃.MCl₂.6H₂O. Thallic beryllium chloride, 2TlCl₃.3BeCl₂,and the ammonia addition-product of thallic cupric iodide, 2TlI₃.CuI₂.4NH₃, have also been described.