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Cadmium iodide
IUPAC name	Cadmium(II) iodide
Other names	Cadmium diiodide
Identifiers
CAS number	7790-80-9 Y
EC number	232-223-6
Properties
Molecular formula	CdI2
Molar mass	366.22 g/mol
Appearance	white to pale yellow crystals
Density	5.640 g/cm3, solid
Melting point	387 °C, 660 K, 729 °F
Boiling point	742 °C, 1015 K, 1368 °F
Solubility in water	78.7 g/100 mL (0 °C) 84.7 g/100 mL (20 °C) 125 g/100 mL (100 °C)
Solubility	soluble in ethanol, acetone, ether and ammonia
Structure
Crystal structure	Rhombohedral, hP3, SpaceGroup = P-3m1, No. 164
Coordination geometry	octahedral
Hazards
EU Index	048-007-00-8
EU classification	Toxic (T) Harmful (Xn) Dangerous for the environment (N)
R-phrases	R23/25, R33, R68, R50/53
S-phrases	(S2), S22, S45, S60, S61
Related compounds
Other anions	cadmium fluoride cadmium chloride cadmium bromide
Other cations	zinc iodide mercury(II) iodide
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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.

Uses

Cadmium iodide is used in lithography, photography, electroplating and the manufacturing of phosphors. ^[1]

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.

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 cubic close-packed structure, while the cadmium cations occupy all of the octahedral interstices

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;

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

Others

AgF₂, W₂C.

References

1. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.