Thallium triiodide is a chemical compound of
thallium
Thallium is a chemical element with the Symbol (chemistry), symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists W ...
and
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
with formula . Unlike the other
thallium trihalides, which contain thallium(III), is a thallium(I) salt and contains the
triiodide
In chemistry, triiodide usually refers to the triiodide ion, . This anion, one of the polyhalogen ions, is composed of three iodine atoms. It is formed by combining aqueous solutions of iodide salts and iodine. Some salts of the anion have bee ...
ion, .
An appreciation as to why Tl
+ is not oxidised to Tl
3+ in the reaction:
: Tl
3+ + 2 I
− → Tl
+ + I
2
can be gained by considering the
standard reduction potentials of the half cells which are:
: Tl
3+ + 2 → Tl
+;''E
r''° = 1.252
: I
2 + 2 → 2 I
−;''E
r''° = 0.5355
The favoured reaction is therefore the reduction of Tl
3+ 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. TlI
3 is no exception as it is possible to stabilise thallium(III) with excess I
− forming the ion (
isoelectronic
Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in the ...
with the
tetraiodomercurate anion and with
lead(IV) iodide).
Structure and preparation
TlI
3 is formulated , and has a similar structure to NH
4I
3, CsI
3 and RbI
3.
The triiodide ion in TlI
3 is nearly linear but is asymmetric with one iodine–iodine bond longer than the other. For comparison the dimensions of the triiodide, I
a–I
b–I
c, ions in the different compounds are shown below:
TlI
3 can be prepared by the evaporation of stoichiometric quantities of
thallium(I) iodide
Thallium(I) iodide is a chemical compound with the formula TlI. It is unusual in being one of the few water-insoluble metal iodides, along with AgI, CuI, SnI2, SnI4, PbI2 and HgI2.
Chemistry
TlI can be formed in aqueous solution by metathes ...
() and
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
in concentrated aqueous
hydriodic acid
Hydroiodic acid (or hydriodic acid) is an aqueous solution of hydrogen iodide (HI). It is a strong acid, one that is ionized completely in an aqueous solution. It is colorless. Concentrated solutions are usually 48% to 57% HI.
Reactions
Hy ...
, or by reacting TlI with iodine in
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
.
References
WebElements*
{{Thallium compounds
Thallium(I) compounds
Iodides
Metal halides
Polyhalides