Cobalt(II) iodide

Cobalt(II) iodide or cobaltous iodide are the inorganic compounds with the formula CoI₂ and the hexahydrate CoI₂(H₂O)₆. These salts are the principal iodides of cobalt.^[2]

Cobalt(II) iodide

Names
IUPAC name Cobalt(II) iodide
Other names cobaltous iodide, cobalt diiodide
Identifiers
CAS Number	15238-00-3 (HCl) Y 52595-03-6 (hexahydrate) N
3D model (JSmol)	Interactive image
ChemSpider	76542 N
ECHA InfoCard	100.035.697
EC Number	239-283-2
PubChem CID	419951
UNII	RTJ1W9DF34 Y
CompTox Dashboard (EPA)	DTXSID301014304 DTXSID00329389, DTXSID301014304
InChI InChI=1S/Co.2HI/h;2*1H/q+2;;/p-2 N Key: AVWLPUQJODERGA-UHFFFAOYSA-L N InChI=1/Co.2HI/h;2*1H/q+2;;/p-2 Key: AVWLPUQJODERGA-NUQVWONBAD
SMILES [Co+2].[I-].[I-]
Properties
Chemical formula	CoI2
Molar mass	312.7421 g/mol (anhydrous) 420.83 g/mol (hexahydrate)
Appearance	α-form: black hexagonal crystal β-form: yellow powder
Density	α-form: 5.584 g/cm3 β-form: 5.45 g/cm3 hexahydrate: 2.79 g/cm3
Melting point	α-form: 515-520 °C under vacuum β-form: converts to α-form at 400 °C
Boiling point	570 °C (1,058 °F; 843 K)
Solubility in water	67.0 g/100 mL[1]
Magnetic susceptibility (χ)	+10,760·10−6 cm3/mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312, H315, H319, H332, H335
NFPA 704 (fire diamond)	3 0 1
Related compounds
Other anions	Cobalt(II) fluoride Cobalt(II) chloride Cobalt(II) bromide
Other cations	Nickel(II) iodide Copper(I) iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis

Cobalt(II) iodide is prepared by treating cobalt powder with gaseous hydrogen iodide.^[2] The hydrated form CoI₂.6H₂O can be prepared by the reaction of cobalt(II) oxide (or related cobalt compounds) with hydroiodic acid.

Cobalt(II) iodide crystallizes in two polymorphs, the α- and β-forms. The α-polymorph consists of black hexagonal crystals, which turn dark green when exposed to air. Under a vacuum at 500 °C, samples of α-CoI₂ sublime, yielding the β-polymorph as a yellow crystals. β-CoI₂ also readily absorbs moisture from the air, converting into green hydrate. At 400 °C, β-CoI₂ reverts to the α-form.^[2]

Structures

The anhydrous salts adopt the cadmium halide structures.

The hexaaquo salt consists of separated [Co(H₂O)₆]²⁺ and iodide ions as verified crystallographically.^[3][4]

Reactions and applications

Anhydrous cobalt(II) iodide is sometimes used to test for the presence of water in various solvents.^[5]

Cobalt(II) iodide is used as a catalyst, e.g. in carbonylations. It catalyzes the reaction of diketene with Grignard reagents, useful for the synthesis of terpenoids^[6]