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
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.294
EC Number
  • 232-223-6
PubChem CID
UNII
CompTox Dashboard (EPA)
Properties
Chemical formula
 CdI2
Molar mass 366.22 g/mol
Appearance white to pale yellow crystals
Density 5.640 g/cm3, 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 cm3/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/m3 (as Cd)[1]
REL (Recommended)
 Ca[1]
IDLH (Immediate danger)
 Ca [9 mg/m3 (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

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

Compounds with the CdI2 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.

Iodides

MgI2, TiI2, VI2, MnI2, FeI2, CoI2, CaI2, PdI2, PbI2.

Chlorides and bromides

TiCl2, VCl2;

MgBr2, TiBr2, VBr2, MnBr2, FeBr2, CoBr2.

Hydroxides of M2+

Mg(OH)2, Ni(OH)2, Ca(OH)2.

Chalcogenides of M4+

TiS2, ZrS2, SnS2, α-TaS2, PtS2;

TiSe2, ZrSe2, SnSe2, PtSe2; CrSe2

SiTe2, TiTe2, CoTe2, NiTe2, PdTe2, PtTe2.

Others

AgF2, W2C.

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.
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