Mercury(II) iodide

Mercury(II) iodide

Mercury(II) iodide (α form)
Mercury(II) iodide (β form)
β (left) and α (right) forms
Names
IUPAC name Mercury diiodide
Other names Mercuric iodide Red mercury (α form only)
Identifiers
CAS Number	7774-29-0 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:49659 Y
ChemSpider	22893 Y
DrugBank	DB04445 Y
ECHA InfoCard	100.028.976
PubChem	24485
UNII	R03O05RB0P Y
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
SMILES I[Hg]I
Properties
Chemical formula	HgI2
Molar mass	454.40 g/mol
Appearance	orange-red powder
Odor	odorless
Density	6.36 g/cm3
Melting point	259 °C (498 °F; 532 K)
Boiling point	350 °C (662 °F; 623 K)
Solubility in water	0.006 g/100 mL
Solubility	slightly soluble in alcohol, ether, acetone, chloroform, ethyl acetate, CS2, olive oil, castor oil
Magnetic susceptibility (χ)	−128.6·10−6 cm3/mol
Refractive index (nD)	2.455
Structure
Crystal structure	tetrehedral
Pharmacology
ATC code	D08AK30 (WHO)
Hazards
EU classification (DSD)	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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
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.

Mercury(II) iodide is produced by adding an aqueous solution of potassium iodide to an aqueous solution of mercury(II) chloride with stirring; the precipitate is filtered off, washed and dried at 70 °C.

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.

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