Thallium triiodide

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.
An appreciation as to why Tl is not oxidised to Tl in the reaction: