Mercury(I) iodide

Mercury(I) iodide

Names
IUPAC name Mercury(I) iodide
Other names Mercurous iodide Red mercury
Identifiers
CAS Number	15385-57-6 Y
ChemSpider	21160367 N
EC Number	239-409-6
Jmol 3D model	Interactive image
PubChem	27243
UN number	1638
InChI InChI=1S/2Hg.2I N Key: PRZLIHOGWOTIQA-UHFFFAOYSA-N N
SMILES [I]1=[Hg]2[I]=[Hg]12
Properties
Chemical formula	Hg 2I 2
Molar mass	654.99 g mol−1
Appearance	Dark yellow, opaque crystals
Odor	Odourless
Density	7.7 g mL−1
Thermochemistry
Std molar entropy (So298)	241.47 J K−1 mol−1
Std enthalpy of formation (ΔfHo298)	−119.09 kJ mol−1
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Mercury(I) iodide is a chemical compound of mercury and iodine. The chemical formula is Hg₂I₂. It is photosensitive and decomposes easily to mercury and HgI₂.

Synthesis

Mercury(I) iodide can be prepared by direct combination of mercury and iodine:

2 Hg + I₂ → Hg₂I₂

Structure

In common with other Hg(I) (mercurous) compounds which contain linear X-Hg-Hg-X units, Hg₂I₂ contains linear IHg₂I units with an Hg-Hg bond length of 272 pm (Hg-Hg in the metal is 300 pm) and an Hg-I bond length of 268 pm. The overall coordination of each Hg atom is octahedral as it has in addition to the two nearest neighbours there are four other I atoms at 351 pm. The compound is often formulated as Hg₂²⁺ 2I⁻.

Historical Uses

Mercury(I) iodide, called Protiodide, was a very commonly used drug in the 19th century, prescribed for everything from acne to kidney disease. It was also the treatment of choice for syphilis. It was available over the counter at any drugstore in the world, the most common form being a concoction of protiodide, licorice, glycerin and marshmallow.

Taken orally, and in low doses, protiodide causes excessive salivation, fetid breath, spongy and bleeding gums and sore teeth. Excessive use or an overdose causes physical weakness, loss of teeth, hemolysing (destruction of the red blood cells) of the blood and necrosis of the bones and tissues of the body. Early signs of an overdose or excessive use are muscular tremors, chorea, and locomotor ataxia. Violent bloody vomiting and voiding also occur.

Protiodide is banned as a medication, even though it persisted in use as a quack remedy until the early 20th century.

See also

• Mercury(II) iodide, HgI₂