Cobalt iodide or cobaltous iodide is the inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 composed with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 Co

Cobalt

Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

 I

Iodide

An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...

₂. 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 gas

Gas

Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

eous hydrogen iodide

Hydrogen iodide

Hydrogen iodide is a diatomic molecule. Aqueous solutions of HI are known as iohydroic acid or hydroiodic acid, a strong acid. Gas and aqueous solution are interconvertible...

. The hydrated form (CoI₂(H₂O)₆) can be prepared by the reaction of cobalt(II) oxide

Cobalt(II) oxide

Cobalt oxide or cobalt monoxide is an inorganic compound that appears as olive-green to red crystals, or as a greyish or black powder...

 (or relate cobalt compounds) with hydroiodic acid.

Cobalt(II) iodide crystallizes in two polymorph

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

s, 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.

Reactions and applications

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

Cobalt(II) iodide is used as a catalyst, e.g. in carbonylation

Carbonylation

Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry.-Organic chemistry:...

s. It catalyzes the reaction of diketene

Diketene

Diketene is an organic compound formed by dimerization of ketene. Diketene is a member of the oxetane family. It is used as a chemical reagent in organic chemistry. It is a colorless liquid and heating regenerates the ketene monomer...

 with Grignard reagents, useful for the synthesis of terpenoids