Mercury(I) iodide is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

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 directly reacting mercury and iodine.

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. Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications 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 was a commonly used as a drug in the 19th century, sometimes under the contemporary name of protiodide of mercury. It was used to treat a wide range of conditions; everything from

acne Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...

to kidney disease and in particular was 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 Liquorice (British English) or licorice (American English) ( ; also ) is the common name of ''Glycyrrhiza glabra'', a flowering plant of the bean family Fabaceae, from the root of which a sweet, aromatic flavouring can be extracted. The liq ...

glycerin Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

and

marshmallow Marshmallow (, ) is a type of confectionery that is typically made from sugar, water and gelatin whipped to a solid-but-soft consistency. It is used as a filling in baking or normally molded into shapes and coated with corn starch. The sugar c ...

. Taken orally, and in low doses, protiodide causes excessive salivation, fetid breath, spongy and bleeding gums and sore

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...

. Excessive use or an overdose causes physical weakness, loss of teeth, hemolysing (destruction of the

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

s) of the blood and necrosis of the bones and tissues of the body. Early signs of an

overdose A drug overdose (overdose or OD) is the ingestion or application of a drug or other substance in quantities much greater than are recommended.

or excessive use are muscular tremors,

chorea Chorea (or choreia, occasionally) is an abnormal involuntary movement disorder, one of a group of neurological disorders called dyskinesias. The term ''chorea'' is derived from the grc, χορεία ("dance"; see choreia), as the quick movem ...

, and

locomotor ataxia Locomotor ataxia is the inability to precisely control one's own bodily movements. __TOC__ Disease People afflicted with this disease may walk in a jerky, non-fluid manner. They will not know where their arms and legs are without looking (i.e. a f ...

. Violent bloody

vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteri ...

and

voiding Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...

also occur. Protiodide is banned as a

medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...

, even though it persisted in use as a

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remedy until the early 20th century.

References

{{Iodides Iodides Metal halides Mercury(I) compounds Withdrawn drugs

Synthesis

Structure

Historical Uses

See also

References