Mercury(II) iodide

Mercury(II) iodide
Mercury(II) iodide (α form)
Mercury(II) iodide (β form)
α (right) and β (left) forms
IUPAC name Mercury diiodide
Other names Mercuric iodide
Identifiers
CAS number	7774-29-0 Y
ChemSpider	22893 Y
UNII	R03O05RB0P Y
DrugBank	DB04445
ChEBI	CHEBI:49659 Y
Jmol-3D images	Image 1
SMILES I[Hg]I
InChI InChI=1S/Hg.2HI/h;2*1H/q+2;;/p-2 Y Key: YFDLHELOZYVNJE-UHFFFAOYSA-L Y InChI=1/Hg.2HI/h;2*1H/q+2;;/p-2 Key: YFDLHELOZYVNJE-NUQVWONBAE
Properties
Molecular formula	HgI2
Molar mass	454.40 g/mol
Appearance	orange-red powder
Density	6.36 g/cm3
Melting point	259 °C
Boiling point	350 °C
Solubility in water	0.06 g/L
Hazards
EU Index	080-002-00-6
EU classification	Very toxic (T+) Dangerous for the environment (N)
R-phrases	R26/27/28, R33, R50/53
S-phrases	(S1/2), S13, S28, S45, S60, S61
NFPA 704	0 3 0
Flash point	Non-flammable
Related compounds
Other anions	Mercury(II) fluoride Mercury(II) chloride Mercury(II) bromide
Other cations	Zinc iodide Cadmium iodide
Related compounds	Mercury(I) iodide
Y iodide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 (<100 ppm).

Conditions/substances to avoid include: heat, light, bromides, chlorides, ammonia, alkalis, cyanides, copper salts, lead salts, iodoform and hydrogen peroxide.

Mercury(II) iodide displays thermochromism; when heated above 126 °C, it undergoes phase transition from the alpha crystalline form to a pale yellow beta form. As the sample cools, it gradually reacquires its original color. It is often used for thermochromism demonstrations.^[1]

Mercury(II) iodide is used for preparation of Nessler's reagent, used for detection of presence of ammonia.

Mercury(II) iodide is a semiconductor material, used in some x-ray and gamma ray detection and imaging devices operating at room temperatures.^[2]

Mercury(II) iodide can be found extremely rarely in nature as mineral coccinite.

In veterinary medicine, mercury(II) iodide is used in blister ointments in exostoses, bursal enlargement, etc.

It can appear as a precipitate in many reactions.

References

1. ^ Thermochromism: Mercury(II) Iodide. Jchemed.chem.wisc.edu. Retrieved on 2011-06-02.
2. ^ Simage, Oy U.S. Patent 6,509,203 Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003