Thallium halide

The thallium halides come in two oxidation states: monohalides, where thallium has the oxidation state +1, and trihalides, where thallium generally has oxidation state +3.

Monohalides

Thallium(I) iodide has a distorted rock salt structure

The monohalides all contain thallium with oxidation state +1.

• Thallium(I) fluoride, a white crystalline solid. It is soluble in water, unlike the other thallium monohalides.
• Thallium(I) chloride, sensitive to light. It is a white crystalline solid.
• Thallium(I) bromide, sensitive to light. A pale yellow crystalline solid.
• Thallium(I) iodide, at room temperature it is a yellow crystalline solid. At higher temperatures the colour changes to red.

Trihalides

Thallium(III) halides are very rare. Some of them are unstable. The thallium(III) iodide does not form. They are quite different to aluminium, gallium and indium trihalides.

• Thallium(III) fluoride, also known as thallic fluoride, is made of thallium in its +3 oxidation state and fluoride ions. It is made by reacting thallium(III) oxide with bromine trifluoride, fluorine, or sulfur tetrafluoride at a warm temperature.
• Thallium(III) chloride, also known as thallic chloride, is made of thallium in its +3 oxidation state and chloride ions. It disproportionates above 40°C, making thallium(I) chloride and chlorine. It is made by reacting thallium(I) chloride with chlorine in an organic solution.
• Thallium(III) bromide, also known as thallic bromide, is made of thallium in its +3 oxidation state and bromide ions. It disproportionates at a low temperature to thallium(I) bromide and bromine. It can be made by reacting thallium(I) bromide with bromine in water or an organic solution.
• Thallium(I) triiodide, a black crystalline solid. It does not contain thallium(III), but has the same structure as CsI₃ containing the linear I₃^- ion.