Cobalt(II) iodide

Cobalt(II) iodide
IUPAC name
Cobalt(II) iodide
Other names
cobaltous iodide, cobalt diiodide
15238-00-3 N
52595-03-6 (hexahydrate) N
3D model (Jmol) Interactive image
ChemSpider 76542 N
ECHA InfoCard 100.035.697
PubChem 419951
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)
67.0 g/100 mL[1]
Harmful (Xn)
R-phrases R20/21/22, R36/37/38
S-phrases S26, S36[2]
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
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).
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Infobox references

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.[3]


Cobalt(II) iodide is prepared by treating cobalt powder with gaseous hydrogen iodide.[3] The hydrated form (CoI2(H2O)6) can be prepared by the reaction of cobalt(II) oxide (or relate 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 sublimes, 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.[3]


The anhydrous salts adopt the cadmium halide structures.

The hexaaquo salt consists of separated [Co(H2O)6]2+ and iodide ions as verified crystallographically.[4][5]

Reactions and applications

Anhydrous cobalt(II) iodide is sometimes used to test for the presence of water in various solvents.[6]

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[7]


  1. Perry, Dale L.; Phillips, Sidney L. (1995), Handbook of Inorganic Compounds, San Diego: CRC Press, pp. 127–8, ISBN 0-8493-8671-3, retrieved 2008-06-03
  2. "429740 Cobalt(II) iodide anhydrous, beads, −10 mesh, 99.999%". Sigma-Aldrich. Retrieved 2008-06-03.
  3. 1 2 3 O. Glemser "Cobalt, Nickel" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1518.
  4. “Structure Cristalline et Expansion Thermique de L’Iodure de Nickel Hexahydrate“ (Crystal structure and thermal expansion of nickel(II) iodide hexahydrate) Louër, Michele; Grandjean, Daniel; Weigel, Dominique Journal of Solid State Chemistry (1973), 7(2), 222-8. doi: 10.1016/0022-4596(73)90157-6
  5. "The crystal structure of the crystalline hydrates of transition metal salts. The structure of CoI2·6H2O" Shchukarev, S. A.; Stroganov, E. V.; Andreev, S. N.; Purvinskii, O. F. Zhurnal Strukturnoi Khimii 1963, vol. 4, pp. 63-6.<!no doi in CAS-->
  6. Armarego, Wilfred L. F.; Chai, Christina L. L. (2003), Purification of Laboratory Chemicals, Butterworth-Heinemann, p. 26, ISBN 0-7506-7571-3, retrieved 2008-06-03
  7. Agreda, V. H.; Zoeller, Joseph R. (1992), Acetic Acid and Its Derivatives, CRC Press, p. 74, ISBN 0-8247-8792-7, retrieved 2008-06-03
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