Cobalt(II) iodide

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Cobalt(II) iodide
Names
IUPAC name
Cobalt(II) iodide
Other names
cobaltous iodide, cobalt diiodide
Identifiers
(hexahydrate: 52595-03-6) 15238-00-3 (hexahydrate: 52595-03-6) N
PubChem 419951
Properties
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)
67.0 g/100 mL[1]
Vapor pressure {{{value}}}
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 is the inorganic compound composed with the formula CoI2. The two forms of CoI2 and the hexahydrate CoI2(H2O)6 are the principal iodides of cobalt.[2]

Synthesis and structure

Cobalt(II) iodide is prepared by treating cobalt powder with gaseous hydrogen iodide.[2] 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. Heating samples of α-CoI2 under a vacuum at 500 C causes sublimation, yielding the β-polymorph is a yellow crystals. β-CoI2 also readily absorbs moisture from the air, converting into green droplets. Upon heating to 400 °C, β-CoI2 converts to the α-form.[2]

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]

References

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  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 O. Glemser "Cobalt, Nickel" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1518.
  3. ↑ “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
  4. ↑ "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.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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