Cadmium iodide

Cadmium iodide, CdI₂, is a chemical compound of cadmium and iodine. It is notable for its crystal structure, which is typical for compounds of the form MX₂ with strong polarization effects.

Cadmium iodide

Names
IUPAC name Cadmium(II) iodide
Other names Cadmium diiodide
Identifiers
CAS Number	7790-80-9
3D model (JSmol)	Interactive image
ChemSpider	23037
ECHA InfoCard	100.029.294
EC Number	232-223-6
PubChem CID	277692
UNII	2F2UPU4KCW
CompTox Dashboard (EPA)	DTXSID20894887
InChI InChI=1S/Cd.2HI/h;2*1H/q+2;;/p-2 Key: OKIIEJOIXGHUKX-UHFFFAOYSA-L InChI=1/Cd.2HI/h;2*1H/q+2;;/p-2 Key: OKIIEJOIXGHUKX-NUQVWONBAZ
SMILES [Cd+2].[I-].[I-]
Properties
Chemical formula	CdI2
Molar mass	366.22 g/mol
Appearance	white to pale yellow crystals
Density	5.640 g/cm^3, solid
Melting point	387 °C (729 °F; 660 K)
Boiling point	742 °C (1,368 °F; 1,015 K)
Solubility in water	787 g/L (0 °C) 847 g/L (20 °C) 1250 g/L (100 °C)
Solubility	soluble in ethanol, acetone, ether and ammonia
Magnetic susceptibility (χ)	-117.2·10^−6 cm^3/mol
Structure
Crystal structure	Trigonal, hP3, space group P3m1, No. 164
Coordination geometry	octahedral
Hazards
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H301, H331, H351, H373, H400, H410
GHS precautionary statements	P260, P280, P301+330+331, P310, P304+340, P311, P403+233
NFPA 704 (fire diamond)	0 3 0
NIOSH (US health exposure limits):
PEL (Permissible)	[1910.1027] TWA 0.005 mg/m^3 (as Cd)[1]
REL (Recommended)	Ca[1]
IDLH (Immediate danger)	Ca [9 mg/m^3 (as Cd)][1]
Related compounds
Other anions	cadmium fluoride cadmium chloride cadmium bromide
Other cations	zinc iodide mercury(II) 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

Preparation

Cadmium iodide is prepared by the addition of cadmium metal, or its oxide, hydroxide or carbonate to hydroiodic acid.

Also, the compound can be made by heating cadmium with iodine.

Crystal structure

The iodide anions in CdI₂ form a hexagonal close-packed lattice, while the cadmium cations occupy all of the octahedral holes in alternating layers.

In cadmium iodide the iodide anions form a hexagonal close packed arrangement while the cadmium cations fill all of the octahedral sites in alternate layers. The resultant structure consists of a layered lattice. This same basic structure is found in many other salts and minerals. Cadmium iodide is mostly ionically bonded but with partial covalent character.[2]

Cadmium iodide's crystal structure is the prototype on which the crystal structures many other compounds can be considered to be based. Compounds with any of the following characteristics tend to adopt the CdI₂ structure:

• Iodides of moderately polarising cations; bromides and chlorides of strongly polarising cations
• Hydroxides of dications, i.e. compounds with the general formula M(OH)₂
• Sulfides, selenides and tellurides (chalcogenides) of tetracations, i.e. compounds with the general formula MX₂, where X = S, Se, Te

References

1. NIOSH Pocket Guide to Chemical Hazards. "#0087". National Institute for Occupational Safety and Health (NIOSH).
2. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1211–1212. ISBN 978-0-08-037941-8.