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|R-phrases (outdated)||R26/27/28, R33, R50/53|
|S-phrases (outdated)||(S1/2), S13, S28, S45, S60, S61|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
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.
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 orange form 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.
It can appear as a precipitate in many reactions.