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Thallium(I) iodide



Thallium(I) iodide
General
Other names thallium monoiodide
thallous iodide
Molecular formula TlI
Molar mass 331.2878 g/mol
Appearance yellow crystals
red crystals above 170 °C
CAS number [7790-30-9]
Properties
Density and phase 7.29 g/cm3, solid
Solubility in water insoluble
Melting point 442°C
Boiling point 823°C
Hazards
EU classification not listed
NFPA 704
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Thallium(I) iodide (TlI) is a chemical compound of formula TlI. It is unusual in being one of the few water-insoluble metal iodides, along with AgI, PbI2 and HgI2.

TlI can be formed in aqueous solution by metathesis of any soluble thallium salt with iodide ion. It is also formed as a by-product in thallium-promoted iodination of phenols with thallium(I) acetate.

Attempts to oxidise TlI to thallium(III) iodide fail, since oxidation produces the thallium(I) triiodide, Tl+I3.

Yellow TlI has an orthorhombic structure which can be considered to be a distorted NaCl structure. The distorted structure is believed to be caused by favourable thallium-thallium interactions, the closest Tl-Tl distance is 383pm.[1] At 175oC it transforms to a red CsCl form. Under high pressure, 160kbar, it becomes a metallic conductor.

Applications include:

  • Added to mercury arc lamps to improve their performance [2] The light produced is mainly in the blue green part of the visible light spectrum least absorbed by water, so these have been used for underwater lighting.[3]
  • Used in trace amounts with NaI or CsI to produce a scintillator used in radiation scintillation detectors.

Thallium(I) iodide is, like all thallium compounds, highly toxic. Conditions/substances to avoid are: heat.


See also

  • Thallium halides
  • Thallium(I) chloride


General references

  • WebElements
  • Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Thallium(I)_iodide". A list of authors is available in Wikipedia.
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