mercury(II) iodide
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 470454715
| Name = Mercury(II) iodide
| ImageFile = Mercury(II)-iodide-xtal-3D-SF-A.png
| ImageSize =
| ImageCaption = Mercury(II) iodide (α form)
| ImageFile1 = Mercury(II)-iodide-xtal-3D-SF-B.png
| ImageSize1 =
| ImageCaption1 = Mercury(II) iodide (β form)
| ImageFile2 = Mercury iodide.jpg
| ImageCaption2 = β (left) and α (right) forms
| IUPACName = Mercury(II) iodide
| OtherNames = Mercury diiodide
Mercuric iodide
Red mercury (α form only)
Coccinite (α form only)
|Section1={{Chembox Identifiers
| CASNo = 7774-29-0
| CASNo_Ref = {{cascite|correct|CAS}}
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 49659
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 22893
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB04445
| EINECS = 231-873-8
| Gmelin = 277788
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = R03O05RB0P
| PubChem = 24485
| InChI = 1/Hg.2HI/h;2*1H/q+2;;/p-2
| InChIKey = YFDLHELOZYVNJE-NUQVWONBAE
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Hg.2HI/h;2*1H/q+2;;/p-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = YFDLHELOZYVNJE-UHFFFAOYSA-L
| SMILES = I[Hg]I
}}
|Section2={{Chembox Properties
| Formula = HgI2
| MolarMass = 454.40 g/mol
| Appearance = orange-red powder
| Odor = odorless
| Density = 6.36 g/cm3
| Solubility = 6 mg/100 mL
| SolubleOther = slightly soluble in alcohol, ether, acetone, chloroform, ethyl acetate, CS2, olive oil, castor oil
Soluble in excess KI(Potassium iodide) forming soluble complex K2[HgI4 ](Potassium tetraiodomercurate(II)) also known as Nessler's reagent
| SolubilityProduct = 2.9{{e|−29}}{{cite book |author1=John Rumble |title=CRC Handbook of Chemistry and Physics |date=June 18, 2018 |publisher=CRC Press |isbn=978-1138561632 |pages=5–189|edition=99 |language=English}}
| MeltingPtC = 259
| BoilingPtC = 350
| RefractIndex = 2.455
| MagSus = −128.6·10−6 cm3/mol
}}
|Section3={{Chembox Structure
| CrystalStruct = Tetrahedral
}}
|Section6={{Chembox Pharmacology
| ATCCode_prefix = D08
| ATCCode_suffix = AK30
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| GHSPictograms = {{GHS06}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|300|310|330|373|410}}
| PPhrases = {{P-phrases|260|262|264|270|271|273|280|284|301+310|302+350|304+340|310|314|320|321|322|330|361|363|391|403+233|405|501}}
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| FlashPt = Non-flammable
| PEL =
}}
|Section8={{Chembox Related
| OtherAnions = Mercury(II) fluoride
Mercury(II) chloride
Mercury(II) bromide
| OtherCations = Zinc iodide
Cadmium iodide
| OtherCompounds = Mercury(I) iodide
}}
}}
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).
Production
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 + 2 KCl
Properties
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 been used for thermochromism demonstrations.[http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA2/MAIN/THERMHG/CD2R1.HTM Thermochromism: Mercury(II) Iodide]. Jchemed.chem.wisc.edu. Retrieved on 2011-06-02. 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.{{cite journal|last1=SCHWARZENBACH|first1=D.|title=The crystal structure and one-dimensional disorder of the orange modification of HgI2|journal=Zeitschrift für Kristallographie - Crystalline Materials|date=1 January 1969|volume=128|issue=1–6|pages=97–114|doi=10.1524/zkri.1969.128.16.97|s2cid=96682743}} The various forms can exist in a diverse range of crystal structures and as a result mercury(II) iodide possesses a surprisingly complex phase diagram.{{cite journal|last1=Hostettler|first1=Marc|last2=Schwarzenbach|first2=Dieter|title=Phase diagrams and structures of HgX2 (X = I, Br, Cl, F)|journal=Comptes Rendus Chimie|date=February 2005|volume=8|issue=2|pages=147–156|doi=10.1016/j.crci.2004.06.006|url=https://comptes-rendus.academie-sciences.fr/chimie/articles/10.1016/j.crci.2004.06.006/ }}
Uses
File:Crystal in VCGS furnace.jpg]]
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.Simage, Oy {{US patent|6509203}} Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003
In veterinary medicine, mercury(II) iodide is used in blister ointments in exostoses, bursal enlargement, etc. {{Citation needed|reason=Reliable source needed for the whole sentence|date=March 2017}}
It can appear as a precipitate in many reactions.
See also
- Mercury(I) iodide, Hg2I2
References
{{reflist}}
{{Mercury compounds}}
{{Iodides}}
{{Antiseptics and disinfectants}}