Zinc iodide

Zinc iodide

Names
IUPAC name Zinc iodide
Other names Zinc(II) iodide
Identifiers
CAS Number	10139-47-6 Y
ChemSpider	59657 Y
Jmol 3D model	Interactive image
PubChem	66278
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	319.22 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)
Structure
Crystal structure	Tetragonal, tI96
Space group	I41/acd, No. 142
Vapor pressure	{{{value}}}
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).
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Infobox references

Zinc iodide is a chemical compound of zinc and iodine, ZnI₂. The anhydrous form is white and readily absorbs water from the atmosphere. It can be prepared by the direct reaction of zinc and iodine in refluxing ether. or by reacting zinc with iodine in aqueous solution:

Zn + I₂→ ZnI₂

At 1150 °C, zinc iodide vapour dissociates into zinc and iodine.
In aqueous solution the following have been detected, octahedral Zn(H₂O)₆²⁺, [ZnI(H₂O)₅]⁺ and tetrahedral ZnI₂(H₂O)₂, ZnI₃(H₂O)⁻ and ZnI₄²⁻.

The structure of crystalline ZnI₂ is unusual, and while zinc atoms 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. These "super-tetrahedra" are similar to the P₄O₁₀ structure. Molecular ZnI₂ is linear as predicted by VSEPR theory with a Zn-I bond length of 238 pm.

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.
• United States Patent 4109065 describes a rechargeable aqueous zinc-halogen cell which 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 conjunction with osmium tetroxide ZnI₂ is used as a stain in electron microscopy.