Thallium triiodide

Thallium triiodide
Thallium triiodide
Names
IUPAC name
thallium(I) (triiodide)
Other names
thallous triiodide
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 236-627-3
  • InChI=1S/I3.Tl/c1-3-2;/q-1;+1
    Key: CFEVJLSKLTWQJS-UHFFFAOYSA-N
  • [Tl+].I[I-]I
Properties
I3Tl
Molar mass 585.09 g·mol−1
Hazards
GHS labelling:
GHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard
Danger
H300, H330, H373, H411
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability (red): no hazard codeInstability (yellow): no hazard codeSpecial hazards (white): no code
4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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) salt and contains the triiodide ion, I−
3.

An appreciation as to why Tl+ is not oxidised to Tl3+ in the reaction:

Tl3+ + 2 I− → Tl+ + I2

can be gained by considering the standard reduction potentials of the half cells which are:

Tl3+ + 2
e−
 → Tl+; Er° = 1.252
I2 + 2
e−
 → 2 I−; Er° = 0.5355

The favoured reaction is therefore the reduction of Tl3+ to Tl+ (1.252 > 0.5355).

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(III) with excess I− forming the tetraiodothallate (TlI−
4) ion (isoelectronic with the tetraiodomercurate anion and with lead(IV) iodide).