Cobalt(II) iodide

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Cobalt(II) iodide
Identifiers
CAS number 15238-00-3
PubChem 419951
Properties
Molecular 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: 2.09 g/cm3
Melting point α-form: 515-520°C under vacuum
β-form: converts to α-form at 400°C
Boiling point 570 °C
Solubility in water 67.0 g/100 mL[1]
Hazards
EU classification 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 noted otherwise, 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 Co I2. The two forms of CoI2 and the hydrated form are the principal iodides of cobalt.

Synthesis and structure[edit]

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. 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.[3]

Reactions and applications[edit]

Anhydrous cobalt(II) iodide is sometimes used to test for the presence of water in various solvents.[4]

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[5]

References[edit]

  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. ^ a b Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1518.
  4. ^ 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 
  5. ^ 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