Chemistry:Thallium triiodide
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| Names | |
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| IUPAC name
Thallium(I) triiodide
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| Other names
thallous triiodide
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| TlI 3 | |
| Molar mass | 585.09 g·mol−1 |
| Appearance | black crystalline solid |
| Hazards | |
| GHS pictograms |   
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| GHS Signal word | Danger |
| H300, H330, H373, H411 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other cations
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Related compounds
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Phosphorus heptabromide ([PBr 4]+ [Br 3]− ) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
 verify (what is   ?)
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| Infobox references | |
Thallium triiodide, more precisely thallium(I) triiodide is a chemical compound of thallium and iodine with empirical formula TlI
3. Unlike the other thallium trihalides, which contain thallium(III), TlI
3 is actually a thallium(I) salt containing thallium(I) cations Tl+
and triiodide anions [I
3]−
, and thus has the chemical formula Tl+
[I
3]−
. It is a black crystalline solid.
An appreciation as to why Tl+
is not oxidised to Tl3+ in the reaction:
- Tl3+ + 2 I−
→ Tl+
+ I
2
can be gained by considering the standard reduction potentials of the half-cells which are:
- Tl3+ + 2 e−
→ Tl+
; Er° = 1.252 - I
2 + 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. TlI
3 is no exception as it is possible to stabilise thallium(III) with excess I−
forming the tetraiodothallate(III) ion [TlI
4]−
(isoelectronic with the tetraiodomercurate anion [HgI
4]2− and with lead(IV) iodide PbI
4).
Structure and preparation
TlI
3 is formulated Tl+
[I
3]−
, and has a similar structure to NH
4I
3, CsI
3 and RbI
3.[1] 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, Ia–Ib–Ic, ions in the different compounds are shown below:
| compound | Ia–Ib (pm) | Ib–Ic (pm) | angle (°) |
|---|---|---|---|
| TlI 3 |
306.3 | 282.6 | 177.90 |
| RbI 3 |
305.1 | 283.3 | 178.11 |
| CsI 3 |
303.8 | 284.2 | 178.00 |
| NH 4I 3 |
311.4 | 279.7 | 178.55 |
TlI
3 can be prepared by the evaporation of stoichiometric quantities of thallium(I) iodide (TlI) and iodine in concentrated aqueous hydriodic acid, or by reacting TlI with iodine in ethanol.
References
- WebElements
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- ↑ Tebbe, K.F.; Georgy, U. (1985-12-15). "Die Kristallstrukturen von Rubidiumtriiodid und Thalliumtriiodid" (in de). Acta Crystallographica C 42 (12): 1675–1678. doi:10.1107/S0108270186090972.
| HI | He | ||||||||||||||||
| LiI | BeI2 | BI3 | CI4 | NI3 | I2O4, I2O5, I4O9 |
IF, IF3, IF5, IF7 |
Ne | ||||||||||
| NaI | MgI2 | AlI3 | SiI4 | PI3, P2I4 |
S | ICl, ICl3 |
Ar | ||||||||||
| KI | CaI2 | Sc | TiI4 | VI3 | CrI3 | MnI2 | FeI2 | CoI2 | NiI2 | CuI | ZnI2 | Ga2I6 | GeI2, GeI4 |
AsI3 | Se | IBr | Kr |
| RbI | SrI2 | YI3 | ZrI4 | NbI5 | Mo | Tc | Ru | Rh | Pd | AgI | CdI2 | InI3 | SnI4, SnI2 |
SbI3 | TeI4 | I | Xe |
| CsI | BaI2 | HfI4 | TaI5 | W | Re | Os | Ir | Pt | AuI | Hg2I2, HgI2 |
TlI | PbI2 | BiI3 | Po | AtI | Rn | |
| Fr | RaI2 | Rf | Db | Sg | Bh | Hs | Mt | Ds | Rg | Cn | Nh | Fl | Mc | Lv | Ts | Og | |
| ↓ | |||||||||||||||||
| La | Ce | Pr | Nd | Pm | SmI2 | Eu | Gd | TbI3 | Dy | Ho | Er | Tm | Yb | Lu | |||
| Ac | ThI4 | Pa | UI3, UI4 |
Np | Pu | Am | Cm | Bk | Cf | EsI3 | Fm | Md | No | Lr | |||
 |  |
