Cobalt(II) iodide
Chemical compound
From Wikipedia, the free encyclopedia
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.[2]
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| Names | |
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| IUPAC name
Cobalt(II) iodide | |
| Other names
cobaltous iodide, cobalt diiodide | |
| Identifiers | |
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3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.035.697 |
| EC Number |
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PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| 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] | |
| +10,760·10−6 cm3/mol | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H302, H312, H315, H319, H332, H335 | |
| NFPA 704 (fire 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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Structure
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 sublime, 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. The anhydrous salts adopt the cadmium halide structures.
The hexaaquo salt consists of separated [Co(H2O)6]2+ and iodide ions as verified crystallographically.[3][4]
Synthesis
Cobalt(II) iodide is prepared by treating cobalt powder with gaseous hydrogen iodide[2] The hydrated form CoI2.6H2O can be prepared by the reaction of cobalt(II) oxide (or related cobalt compounds) with hydroiodic acid.
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]