Thallium triiodide


Thallium triiodide is a chemical compound of thallium and iodine with formula. Unlike the other thallium trihalides, which contain thallium, is a thallium compound and contains the triiodide ion, I3−.
An appreciation as to why Tl+ is not oxidised to Tl3+ in the reaction:
can be gained by considering the standard reduction potentials of the half cells which are:
The favoured reaction is therefore the reduction of Tl3+.
Using standard electrode potentials in this way must be done with caution as factors such as complex formation and solvation may affect the reaction. TlI3 is no exception as it is possible to stabilise thallium with excess I− forming the TlI4− ion.

Structure and preparation

is formulated, and has a similar structure to NH4I3, CsI3 and RbI3. The triiodide ion in is nearly linear but is asymmetric with one iodine − iodine bond longer than the other. For comparison the dimensions of the tri-iodide, Ia − Ib − Ic, ions in the different compounds are shown below:
compoundIa − Ib Ib - Ic angle
306.3282.6177.90
305.1283.3178.11
303.8284.2178.00
311.4279.7178.55

can be prepared by the evaporation of stoichiometric quantities of and in concentrated aqueous, or by reacting with in ethanol.