In chemistry, triiodide (sometimes written tri-iodide) can have several meanings. Triiodide primarily refers to the triiodide ion, i3−, a polyatomic anion composed of three iodine atoms. For some chemical compounds, triiodide indicates a salt of the named cation with the triiodide anion. Examples include sodium triiodide, thallium triiodide, and ammonium triiodide, [nh4][i3]. Each of these compounds has a (mono)iodide counterpart.
Thallium triiodide is a chemical compound of thallium and iodine with formula tli3. Unlike the other thallium trihalides, which contain thallium(iii), tli3 is a thallium(i) compound and contains the triiodide ion, i3−.