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Thallium(I) iodide
Encyclopedia
Thallium iodide (Tl
I
) is a chemical compound
of formula TlI. It is unusual in being one of the few water-insoluble metal iodide
s, along with AgI, PbI2
and HgI2
.
with thallium(I) acetate.
Attempts to oxidise
TlI to thallium(III) iodide fail, since oxidation produces the thallium(I) triiodide
, Tl+I3−.
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 iodides such as RbI, CsI, KI, AgI, TlBr and TlCl . Thus, presence of impurities might be responsible for coexistence of the cubic and orthorombic TlI phases at ambient conditions . Under high pressure, 160kbar, TlI becomes a metallic conductor.
.
Thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...
I
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
) is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of formula TlI. It is unusual in being one of the few water-insoluble metal iodide
Iodide
An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
s, along with AgI, PbI2
Lead(II) iodide
Lead iodide or plumbous iodide is a bright yellow solid at room temperature, that reversibly becomes brick red by heating. In its crystalline form it is used as a detector material for high energy photons including x-rays and gamma rays....
and HgI2
Mercury(II) iodide
Mercury iodide is a chemical compound with an appearance of red-orange crystals. Unlike mercury chloride it is hardly soluble in water Mercury(II) iodide (HgI2) is a chemical compound with an appearance of red-orange crystals. Unlike mercury(II) chloride it is hardly soluble in water Mercury(II)...
.
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 phenolsPhenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group...
with thallium(I) acetate.
Attempts to oxidise
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
TlI to thallium(III) iodide fail, since oxidation produces the thallium(I) triiodide
Thallium triiodide
Thallium triiodide is a chemical compound of thallium and iodine with formula TlI3. Unlike the other thallium trihalides, which contain thallium, TlI3 is a thallium compound and contains the triiodide ion, I3−....
, Tl+I3−.
Physical properties
The room temperature form of TlI is yellow and 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. At 175°C the yellow form transforms to a red CsClCaesium chloride
Caesium chloride is the inorganic compound with the formula CsCl. This colorless solid is an important source of caesium ions in a variety of applications. Its crystal structure forms a major structural type where each caesium ion is coordinated by 8 chlorine ions...
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 iodides such as RbI, CsI, KI, AgI, TlBr and TlCl . Thus, presence of impurities might be responsible for coexistence of the cubic and orthorombic TlI phases at ambient conditions . Under high pressure, 160kbar, TlI becomes a metallic conductor.
Applications
- Added to mercury arc lamps to improve their performance 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.
- Used in trace amounts with NaISodium iodideSodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.-Uses:Sodium iodide is commonly used to treat and prevent iodine deficiency....
or CsICaesium iodideCaesium iodide is an ionic compound often used as the input phosphor of an x-ray image intensifier tube found in fluoroscopy equipment....
to produce a scintillatorScintillatorA scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
used in radiation scintillation detectors.
Safety
Thallium(I) iodide is, like all thallium compounds, highly toxic. Conditions/substances to avoid are: heatHeat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
.