Cobalt(II) iodide

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Cobalt(II) iodide
IUPAC name	Cobalt(II) iodide
Other names	cobaltous iodide, cobalt diiodide
Identifiers
CAS number	[15238-00-3]
Properties
Molecular formula	CoI2
Molar mass	312.742 g/mol
Appearance	α-form: black hexagonal crystal β-form: yellow powder
Density	α-form: 5.584 g/cm³ β-form: 5.45 g/cm³
Melting point	α-form: 515-520°C under vacuum β-form: converts to α-form at 400°C
Solubility in water	67.0 g/100 mL[1]
Hazards
EU classification	Harmful (Xn)
NFPA 704	0 1 1
R-phrases	R20/21/22, R36/37/38
S-phrases	S26, S36[2]
Related compounds
Other anions	Cobalt(II) fluoride Cobalt(II) chloride Cobalt(II) bromide
Other cations	Nickel(II) iodide Copper(I) iodide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Cobalt(II) iodide or cobaltous iodide is the chemical compound composed of cobalt and iodine with the formula CoI₂. This hygroscopic crystalline solid is a laboratory reagent used to test for the presence of water in organic solvents or in the atmosphere^[3]. When anhydrous cobalt(II) iodide is added to solvents such as alcohols, ketones, and nitriles, it will turn pick in the presence of water^[4].

[edit] Forms

Cobalt(II) iodide exists in two distinct forms, the α- and β-forms. The α-form consists of black hexagonal crystals which turn dark green when exposed to air. The β-form is a yellow powder which readily absorbs moisture from the air, converting into green droplets. When placed in a vacuum, the α-form sublimes, forming the β-form. When the β-form is heated to 400°C, it converts to the α-form.

[edit] Reactions

Cobalt(II) iodide is formed by heating elemental cobalt in the presence of gaseous hydrogen iodide or elemental iodine vapor^[3].

Cobalt(II) iodide has been used as a catalyst in the reaction of diketene with Grignard reagents in the synthesis of terpenoids^[5].

[edit] References