Cobalt(II) iodide

Cobalt(II) iodide
IUPAC name Cobalt(II) iodide
Other names cobaltous iodide, cobalt diiodide
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	0 3 1
Related compounds
Other anions	Cobalt(II) fluoride Cobalt(II) chloride Cobalt(II) bromide
Other cations	Nickel(II) iodide Copper(I) iodide
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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

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

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

1. ^ Perry, Dale L.; Phillips, Sidney L. (1995), Handbook of Inorganic Compounds, San Diego: CRC Press, pp. 127–8, ISBN 0849386713, http://books.google.com/?id=0fT4wfhF1AsC&pg=PA128&dq=%22Cobalt(II)+iodide%22, retrieved 2008-06-03 
2. ^ "429740 Cobalt(II) iodide anhydrous, beads, −10 mesh, 99.999%". Sigma-Aldrich. https://www.sigmaaldrich.com/ProductLookup.html?ProdNo=429740&Brand=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, pp. 26, ISBN 0750675713, http://books.google.com/?id=SYzm1tx2z3QC&pg=PA26&dq=%22Cobalt(II)+iodide%22, retrieved 2008-06-03 
5. ^ Agreda, V. H.; Zoeller, Joseph R. (1992), Acetic Acid and Its Derivatives, CRC Press, pp. 74, ISBN 0824787927, http://books.google.com/?id=3MjdGp1v1YIC&pg=RA1-PA784&dq=%22Cobalt(II)+iodide%22, retrieved 2008-06-03