Cobalt(II) chloride
Encyclopedia : C : CO : COB : Cobalt(II) chloride
| Cobalt(II) chloride | |
|---|---|
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| General | |
| Systematic name | Cobalt(II) chloride Cobalt dichloride |
| Other names | Cobaltous chloride |
| Molecular formula | CoCl2 |
| Molar mass | 129.84 g/mol (anhydrous) |
| Appearance | see text |
| CAS number | [7646-79-9] (anhydrous) |
| Properties | |
| Density and phase | 3.356 g/cm3, solid |
| Solubility in water | 45 g/100 ml (7 °C) 53 g/100ml (20 °C) |
| Melting point | 735°C |
| Boiling point | 1049°C (1322 K) |
| Structure | |
| Coordination geometry | Octahedral |
| Crystal structure | CdCl2 structure |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Toxic (T) Carc. Cat. 2 Dangerous for the environment (N) |
| NFPA 704 | |
| R-phrases | R49, R22, R42/43, R50/53 |
| S-phrases | S2, S22, S53, S45, S60, S61 |
| Flash point | non flammable |
| RTECS number | ? |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | Cobalt(II) fluoride Cobalt(II) bromide Cobalt(II) iodide |
| Other cations | Rhodium(III) chloride Iridium(III) chloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
Cobalt(II) chloride (CoCl2) is a chemical compound composed of cobalt and chlorine. It is blue when anhydrous, and a deep magenta colour when hydrated- for this reason it is widely used as an indicator for water, for example in drying agents such as silica gel. The magenta hexahydrate is probably the most familiar cobalt compound in the laboratory:
It is ionic and dissolves readily in water and alcohol, and it has the interesting property that a concentrated aqueous solution is red at room temperature, but becomes blue when heated.[#endnote_4] The anhydrous salt is hygroscopic while the hydrated salt is deliquescent
Chemical properties
Since cobalt(II) chloride is soluble in water, it can be used to prepare a variety of cobalt compounds, e.g.,The most common oxidation state for cobalt is +2, so CoCl2 is generally resistant to oxidation. However, in the presence of ammonia or amines, cobalt(II) chloride is easily oxidised (even by oxygen in the air) to give a variety of stable cobalt(III) amine complexes, for example:
The reaction is often performed in the presence of charcoal as a catalyst or hydrogen peroxide is employed in place of air.
Unlike Co(II) complexes, Co(III) complexes are very slow to exchange ligands, so they are said to be kinetically inert. The German chemist Alfred Werner was awarded the Nobel prize in 1913 for his studies on a series of these cobalt(III) compounds, work that led to an understanding of the structures of such coordination compounds.
Regarding the existence of a simple cobalt(III) chloride, CoCl3, the literature is contradictory. The CRC 71 ed[#endnote_2] describes such a compound as known, but Greenwood & Earnshaw [#endnote_1] (which is more recent) states, "Apart from ...CoF3, ....the only known halides of cobalt are the dihalides."
Cobalt(II) chloride is a weak Lewis acid, reacting with chloride ion to produce salts containing the tetrahedral [CoCl4]2- ion. It forms complexes with ligands such as pyridine (see "uses").
Preparation
Cobalt(II) chloride may be prepared in its anhydrous form from cobalt metal and chlorine gas:The hydrated form can be prepared from cobalt(II) hydroxide or cobalt(II) carbonate with hydrochloric acid.
Uses
A popular use for cobalt(II) chloride is for the detection of moisture. For example, in the US calcium sulfate is sold as a drying agent under the trade name [Drierite]. When cobalt(II) chloride is added as an indicator, the drying agent is blue when still active, pink when exhausted, corresponding to the anhydrous and hydrated forms of CoCl2, respectively. Cobalt chloride paper is likewise used to detect the presence of water.In the laboratory, cobalt(II) chloride serves as a starting point for the synthesis of a variety of cobalt compounds. For example, the reaction of 1-norbonyllithium with CoCl2 produces a brown, thermally stable cobalt(IV) tetralkyl[#endnote_5]—the only compound of its kind for which the detailed structure is fully known[3]:
Reaction of anhydrous CoCl2 with cyclopentadienylsodium in THF to give dark-purple cobaltocene, which can readily be oxidised to a Co(III) compound, the cobaltacenium cation which is isoelectronic with ferrocene. CoCl2 also reacts with ligands such as pyridine to produce tetrahedral metal complexes:
- CoCl2 + 2 C5H5N → [CoCl2(C5H5N)2]
Suppliers/Manufacturers
References
- ↑ The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
- ↑ Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
- ↑
- ↑ E. K. Byrne, D. S. Richeson, K. H. Theopold, Journal of the Chemical Society, Chemical Communications, 1491-2 (1986).
- ↑ A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984. ISBN 0198553706.
- ↑ Hill, Petrucci, McCreary, Perry, General Chemistry, 4th ed., Pearson/Prentice Hall, Upper Saddle River, New Jersey, USA. ISBN 0-1314-0283-8.
External links
- [International Chemical Safety Card 0783]
- [National Pollutant Inventory - Cobalt fact sheet]
- [IARC Monograph "Cobalt and Cobalt Compounds"]
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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