Zinc iodide

Zinc iodide is the inorganic compound with the formula ZnI₂. It exists both in anhydrous form and as a dihydrate. Both are white and readily absorb water from the atmosphere. It has no major application.

Zinc iodide

Names
IUPAC name Zinc iodide
Other names Zinc(II) iodide
Identifiers
CAS Number	10139-47-6 Y
3D model (JSmol)	Interactive image
ChemSpider	59657 Y
ECHA InfoCard	100.030.347
PubChem CID	66278
UNII	762R7A0O0B N
CompTox Dashboard (EPA)	DTXSID5064968
InChI InChI=1S/2HI.Zn/h2*1H;/q;;+2/p-2 Y Key: UAYWVJHJZHQCIE-UHFFFAOYSA-L Y InChI=1/2HI.Zn/h2*1H;/q;;+2/p-2 Key: UAYWVJHJZHQCIE-NUQVWONBAB
SMILES I[Zn]I
Properties
Chemical formula	ZnI2
Molar mass	319.19 g/mol
Appearance	white solid
Density	4.74 g/cm3
Melting point	446 °C (835 °F; 719 K)
Boiling point	1,150 °C (2,100 °F; 1,420 K) decomposes
Solubility in water	450 g/100mL (20 °C)
Magnetic susceptibility (χ)	−98.0·10−6 cm3/mol
Structure
Crystal structure	Tetragonal, tI96
Space group	I41/acd, No. 142
Hazards
Flash point	625 °C (1,157 °F; 898 K)
Safety data sheet (SDS)	External MSDS
Related compounds
Other anions	Zinc fluoride Zinc chloride Zinc bromide
Other cations	Cadmium iodide Mercury(I) iodide
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

Preparation

It can be prepared by the direct reaction of zinc and iodine in water^[1][2] or refluxing ether:^[3]

Zn + I₂ → ZnI₂

Absent a solvent, the elements do not combine directly at room temperature.^[4]

Structure as solid, gas, and in solution

The structure of solid ZnI₂ is unusual relative to the dichloride. While zinc centers are tetrahedrally coordinated, as in ZnCl₂, groups of four of these tetrahedra share three vertices to form “super-tetrahedra” of composition {Zn₄I₁₀}, which are linked by their vertices to form a three-dimensional structure.^[5] These "super-tetrahedra" are similar to the P₄O₁₀ structure.^[5][6]

Molecular ZnI₂ is linear as predicted by VSEPR theory with a Zn-I bond length of 238 pm.^[5]

In aqueous solution the following have been detected: Zn(H₂O)₆²⁺, [ZnI(H₂O)₅]⁺, tetrahedral ZnI₂(H₂O)₂, ZnI₃(H₂O)⁻, and ZnI₄²⁻.^[7]

Applications

• Zinc iodide is often used as an x-ray opaque penetrant in industrial radiography to improve the contrast between the damage and intact composite.^[8][9]
• United States patent 4,109,065 ^[10] describes a rechargeable aqueous zinc-halogen cell that includes an aqueous electrolytic solution containing a zinc salt selected from the class consisting of zinc bromide, zinc iodide, and mixtures thereof, in both positive and negative electrode compartments.
• In combination with osmium tetroxide, ZnI₂ is used as a stain in electron microscopy.^[11]
• As a Lewis acid, zinc iodide catalyzes for the conversion of methanol to triptane and hexamethylbenzene.^[12]
• It can be used as a topical antiseptic.^[13]