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Mercury(II) iodide

Mercury(II) iodide
Mercury(II) iodide (α form)
Mercury(II) iodide (β form)
Mercury iodide.jpg
β (left) and α (right) forms
IUPAC name
Mercury(II) iodide
Other names
Mercury diiodide
Mercuric iodide
Red mercury (α form only)
Coccinite (α form only)
3D model (JSmol)
ECHA InfoCard 100.028.976
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)
0.006 g/100 mL
Solubility slightly soluble in alcohol, ether, acetone, chloroform, ethyl acetate, CS2, olive oil, castor oil
−128.6·10−6 cm3/mol
D08AK30 (WHO)
Very toxic (T+)
Dangerous for the environment (N)
R-phrases (outdated) R26/27/28, R33, R50/53
S-phrases (outdated) (S1/2), S13, S28, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
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).
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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).


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 + KCl


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 used for thermochromism demonstrations.[1] A third orange form is also known; this can be formed by recrystallisation and is also metastable, eventually converting back to the red alpha form.[2] The various forms can exist in a diverse range of crystal structures and as a result mercury(II) iodide possess a surprisingly complex phase diagram.[3]


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.[4]

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

It can appear as a precipitate in many reactions.

See also


  1. ^ Thermochromism: Mercury(II) Iodide. Retrieved on 2011-06-02.
  2. ^ 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). doi:10.1524/zkri.1969.128.16.97.
  3. ^ 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.
  4. ^ Simage, Oy U.S. Patent 6,509,203 Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003