Thallium(I) iodide

Thallium(I) iodide
Names
	Other names Thallium monoiodide; Thallous iodide
Identifiers
CAS Number	7790-30-9 ;
3D model (JSmol)	Interactive image;
ChemSpider	56430 ;
ECHA InfoCard	100.029.272
PubChem CID	62679;
UNII	98W17EMO3C ;
CompTox Dashboard (EPA)	DTXSID10894795 ;
	InChI InChI=1S/HI.Tl/h1H;/q;+1/p-1 Key: CMJCEVKJYRZMIA-UHFFFAOYSA-M ; InChI=1/HI.Tl/h1H;/q;+1/p-1 Key: CMJCEVKJYRZMIA-REWHXWOFAG;
	SMILES I[Tl];
Properties
Chemical formula	TlI
Molar mass	331.287 g/mol[1]
Appearance	yellow crystals[1]
Density	7.1 g/cm3[1]
Melting point	441.7 °C (827.1 °F; 714.8 K)[1]
Boiling point	824 °C (1,515 °F; 1,097 K)[1]
Solubility in water	0.085 g/L (25 °C)[1]
Solubility	insoluble in alcohol[1]
Magnetic susceptibility (χ)	−82.2·10−6 cm3/mol[2]
Hazards
EU classification (DSD) (outdated)	Very toxic (T+); Dangerous for the environment (N)
R-phrases (outdated)	R26/28, R33, R51/53
S-phrases (outdated)	(S1/2), S13, S28, S45, S61
Flash point	Non-flammable
Related compounds
Other anions	Thallium(I) fluoride; Thallium(I) chloride; Thallium(I) bromide
Other cations	Gallium(I) iodide; Indium(I) iodide
Related compounds	Mercury(II) iodide; Lead(II) iodide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

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 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, $Tl + I 3 -$ .

Physical properties

The room temperature form of TlI is yellow and has an orthorhombic structure [3] 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 383 pm.[4] At 175 °C the yellow form transforms to a red CsCl form. This phase transition is accompanied by about two orders of magnitude jump in electrical conductivity. The CsI structure can be stabilized down to room temperature by doping $TlI$ with other halides such as RbI, CsI, KI, AgI, TlBr and TlCl.[5] Thus, presence of impurities might be responsible for coexistence of the cubic and orthorombic $TlI$ phases at ambient conditions.[3] Under high pressure, 160 kbar, $TlI$ becomes a metallic conductor. Nanometer-thin $TlI$ films grown on LiF, NaCl or KBr substrates exhibit the cubic rocksalt structure.[6]

Applications

Thallium(I) iodide is added to mercury arc lamps to improve their performance[7] 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.[8] Thallium(I) iodide is also used in trace amounts with NaI or CsI to produce scintillators used in radiation detectors.

Natural occurrence

Natural thallium(I) iodide was only recently found, as a orthorhombic polymorph called nataliyamalikite. It is of a fumarolic origin.[9]

Safety

Like all thallium compounds, thallium(I) iodide is highly toxic.

References

Haynes, p. 4.94
Haynes, p. 4.136
Lowndes, R. P.; Perry, C. H. (1973). "Molecular structure and anharmonicity in thallium iodide". The Journal of Chemical Physics. 58 (1): 271–278. Bibcode:1973JChPh..58..271L. doi:10.1063/1.1678917.
Mudring, Anja-Verena (2007). "Thallium Halides – New Aspects of the Stereochemical Activity of Electron Lone Pairs of Heavier Main-Group Elements". European Journal of Inorganic Chemistry. 2007 (6): 882–890. doi:10.1002/ejic.200600975.
Sultana, Saima; Rafiuddin (2009). "Electrical conductivity in TlI–TiO2 composite solid electrolyte". Physica B: Condensed Matter. 404 (1): 36–40. Bibcode:2009PhyB..404...36S. doi:10.1016/j.physb.2008.10.002.
Schulz, L. G. (1951). "Polymorphism of cesium and thallium halides". Acta Crystallographica. 4 (6): 487–489. doi:10.1107/S0365110X51001641.
Reiling, Gilbert H. (1964). "Characteristics of Mercury Vapor–Metallic Iodide Arc Lamps". Journal of the Optical Society of America. 54 (4): 532. Bibcode:1964JOSA...54..532R. doi:10.1364/JOSA.54.000532.
Underwater Journal and information bulletin, IPC Science and Technology Press, (1973), p 245
"Nataliyamalikite: Mineral information, data and localities". www.mindat.org.

Cited sources

Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. ISBN 1439855110.

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[r1-1] Haynes, p. 4.94

[2] Haynes, p. 4.136

[low-3] Lowndes, R. P.; Perry, C. H. (1973). "Molecular structure and anharmonicity in thallium iodide". The Journal of Chemical Physics. 58 (1): 271–278. Bibcode:1973JChPh..58..271L. doi:10.1063/1.1678917.

[4] Mudring, Anja-Verena (2007). "Thallium Halides – New Aspects of the Stereochemical Activity of Electron Lone Pairs of Heavier Main-Group Elements". European Journal of Inorganic Chemistry. 2007 (6): 882–890. doi:10.1002/ejic.200600975.

[5] Sultana, Saima; Rafiuddin (2009). "Electrical conductivity in TlI–TiO2 composite solid electrolyte". Physica B: Condensed Matter. 404 (1): 36–40. Bibcode:2009PhyB..404...36S. doi:10.1016/j.physb.2008.10.002.

[str-6] Schulz, L. G. (1951). "Polymorphism of cesium and thallium halides". Acta Crystallographica. 4 (6): 487–489. doi:10.1107/S0365110X51001641.

[7] Reiling, Gilbert H. (1964). "Characteristics of Mercury Vapor–Metallic Iodide Arc Lamps". Journal of the Optical Society of America. 54 (4): 532. Bibcode:1964JOSA...54..532R. doi:10.1364/JOSA.54.000532.

[8] Underwater Journal and information bulletin, IPC Science and Technology Press, (1973), p 245

[9] "Nataliyamalikite: Mineral information, data and localities". www.mindat.org.