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 (α form)
Mercury(II) iodide (β form)
β (left) and α (right) forms
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||454.40 g/mol|
|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|
Refractive index (nD)
|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|R-phrases (outdated)||R26/27/28, R33, R50/53|
|S-phrases (outdated)||(S1/2), S13, S28, S45, S60, S61|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 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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. 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 possess a surprisingly complex phase diagram.
Mercury(II) iodide is used for preparation of Nessler's reagent, used for detection of presence of ammonia.
It can appear as a precipitate in many reactions.
- Mercury(I) iodide, Hg2I2
- Thermochromism: Mercury(II) Iodide. Jchemed.chem.wisc.edu. Retrieved on 2011-06-02.
- 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.1918.104.22.168.
- 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.
- Simage, Oy U.S. Patent 6,509,203 Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003