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Mercury(II) iodide

Mercury(II) iodide (α form)
Mercury(II) iodide (β form)
β (left) and α (right) forms
Names
IUPAC name Mercury(II) iodide
Other names Mercury diiodide Mercuric iodide Red mercury (α form only) Coccinite (α form only)
Identifiers
CAS Number	7774-29-0
3D model (JSmol)	Interactive image
ChEBI	CHEBI:49659
ChemSpider	22893
DrugBank	DB04445
ECHA InfoCard	100.028.976
EC Number	231-873-8
Gmelin Reference	277788
PubChem CID	24485
UNII	R03O05RB0P
CompTox Dashboard (EPA)	DTXSID9042124
InChI InChI=1S/Hg.2HI/h;2*1H/q+2;;/p-2Key: YFDLHELOZYVNJE-UHFFFAOYSA-L InChI=1/Hg.2HI/h;2*1H/q+2;;/p-2Key: YFDLHELOZYVNJE-NUQVWONBAE
SMILES II
Properties
Chemical formula	HgI2
Molar mass	454.40 g/mol
Appearance	orange-red powder
Odor	odorless
Density	6.36 g/cm
Melting point	259 °C (498 °F; 532 K)
Boiling point	350 °C (662 °F; 623 K)
Solubility in water	6 mg/100 mL
Solubility product (Ksp)	2.9×10
Solubility	slightly soluble in alcohol, ether, acetone, chloroform, ethyl acetate, CS2, olive oil, castor oil Soluble in excess KI(Potassium iodide) forming soluble complex K2(Potassium tetraiodomercurate(II)) also known as Nessler's reagent
Magnetic susceptibility (χ)	−128.6·10 cm/mol
Refractive index (nD)	2.455
Structure
Crystal structure	Tetrahedral
Pharmacology
ATC code	D08AK30 (WHO)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H300, H310, H330, H373, H410
Precautionary statements	P260, P262, P264, P270, P271, P273, P280, P284, P301+P310, P302+P350, P304+P340, P310, P314, P320, P321, P322, P330, P361, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 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 , 100 kPa). N verify (what is  ?) Infobox references

Mercury(II) iodide is a chemical compound with the molecular formula HgI₂. It is typically produced synthetically but can also be found in nature as the extremely rare mineral coccinite. Unlike the related mercury(II) chloride it is hardly soluble in water (<100 ppm).

Production

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.

HgCl₂ + 2 KI → HgI₂ + 2 KCl

Properties

Mercury(II) iodide displays thermochromism; when heated above 126 °C (400 K) it undergoes a phase transition, from the red alpha crystalline form to a pale yellow beta form. As the sample cools, it gradually reacquires its original colour. It has often been used for thermochromism demonstrations. A third form, which is orange, is also known; this can be formed by recrystallisation and is also metastable, eventually converting back to the red alpha form. The various forms can exist in a diverse range of crystal structures and as a result mercury(II) iodide possesses a surprisingly complex phase diagram.

Uses

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.

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.

See also

• Mercury(I) iodide, Hg₂I₂

References

1. John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
2. Thermochromism: Mercury(II) Iodide. Jchemed.chem.wisc.edu. Retrieved on 2011-06-02.
3. SCHWARZENBACH, D. (1 January 1969). "The crystal structure and one-dimensional disorder of the orange modification of HgI₂". Zeitschrift für Kristallographie - Crystalline Materials. 128 (1–6): 97–114. doi:10.1524/zkri.1969.128.16.97. S2CID 96682743.
4. Hostettler, Marc; Schwarzenbach, Dieter (February 2005). "Phase diagrams and structures of HgX₂ (X = I, Br, Cl, F)". Comptes Rendus Chimie. 8 (2): 147–156. doi:10.1016/j.crci.2004.06.006.
5. Simage, Oy U.S. patent 6,509,203 Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003

• Iodides
• Metal halides
• Mercury(II) compounds
• Semiconductor materials