Editing Cobalt(II) chloride (section)

==Reactions==
In the laboratory, cobalt(II) chloride serves as a common precursor to other cobalt compounds. Generally, diluted aqueous solutions of the salt behave like other cobalt(II) salts since these solutions consist of the {{chem|[|Co|(|H|2|O|)|6|]|2+}} ion regardless of the anion. For example, such solutions give a precipitate of [[cobalt sulfide]] {{chem|CoS}} upon treatment with [[hydrogen sulfide]] {{chem|H|2|S}}.{{cn|date=September 2023}}

===Complexed chlorides===
The hexahydrate and the anhydrous salt are weak [[Lewis acid]]s.  The [[adduct]]s are usually either [[octahedral]] or [[tetrahedral]]. It forms an [[metal-pyridine complex|octahedral complex with pyridine]] ({{chem|C|5|H|5|N}}):<ref name=Long>{{cite journal |doi=10.1021/ic50184a002|title=Crystal and Molecular Structures of ''trans''-Tetrakis(pyridine)dichloroiron(II), -Nickel(II), and -Cobalt(II) and ''trans''-Tetrakis(pyridine)dichloroiron(II) Monohydrate|year=1978|last1=Long|first1=Gary J.|last2=Clarke|first2=Peter J.|journal=Inorganic Chemistry|volume=17|issue=6|pages=1394–1401}}</ref>
:{{chem|CoCl|2}}·6{{chem|H|2|O}} + 4 {{chem|C|5|H|5|N}}  →  {{chem|CoCl|2|(|C|5|H|5|N|)|4}} + 6 {{chem|H|2|O}}
With [[triphenylphosphine]] ({{chem|P(C|6|H|5|)|3}}), a tetrahedral complex results:
:{{chem|CoCl|2}}·6{{chem|H|2|O}} + 2 {{chem|P(C|6|H|5|)|3}} → {{chem|CoCl|2|[P(C|6|H|5|)|3|]|2}} + 6 {{chem|H|2|O}}

Salts of the anionic complex CoCl<sub>4</sub><sup>2−</sup> can be prepared using tetraethylammonium chloride:<ref>{{cite book|author = Gill, N. S.|author2 = Taylor, F. B.| title=[[Inorg. Synth.|Inorganic Syntheses]] | chapter=Tetrahalo Complexes of Dipositive Metals in the First Transition Series |name-list-style = amp|year = 1967|volume = 9|pages = 136–142|doi = 10.1002/9780470132401.ch37|isbn = 9780470132401}}</ref>
:{{chem|CoCl|2}} + 2 [(C<sub>2</sub>H<sub>5</sub>)<sub>4</sub>N]Cl → [(C<sub>2</sub>H<sub>5</sub>)<sub>4</sub>N)]<sub>2</sub>[CoCl<sub>4</sub>]
The tetrachlorocobaltate ion [CoCl<sub>4</sub>]<sup>2−</sup> is the blue ion that forms upon addition of [[hydrochloric acid]] to aqueous solutions of hydrated cobalt chloride, which are pink.

===Reduction===
[[File:Co(norbornyl)4.png|thumb|left|The structure of a cobalt(IV) [[coordination complex]] with the [[norbornyl]] anion]]
Reaction of the anhydrous compound with [[sodium cyclopentadienide]] gives [[cobaltocene]] {{chem|Co|(|C|5|H|5|)|2}}. This 19-electron species is a good reducing agent, being readily oxidised to the yellow [[18-Electron rule|18-electron]] cobaltocenium cation {{chem|[|Co|(|C|5|H|5|)|2|]|+}}.

===Oxidation to cobalt(III)===
Compounds of cobalt in the +3 oxidation state exist, such as [[cobalt(III) fluoride]] {{chem|CoF|3}}, [[cobalt(III) nitrate|nitrate]] {{chem|Co|(|NO|3|)|3}}, and [[cobalt(III) sulfate|sulfate]] {{chem|Co|2|(|SO|4|)||3}}; however, [[cobalt(III) chloride]] {{chem|CoCl|3}} is not stable in normal conditions, and would decompose immediately into {{chem|CoCl|2}} and [[chlorine]].<ref>''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990.</ref>

On the other hand, cobalt(III) chlorides can be obtained if the cobalt is bound also to other ligands of greater Lewis basicity than chloride, such as [[amine]]s.  For example, in the presence of [[ammonia]], cobalt(II) chloride is readily [[redox|oxidised]] by atmospheric [[oxygen]] to [[hexamminecobalt(III) chloride]]:
:4 {{chem|CoCl|2}}·6{{chem|H|2|O}} + 4 {{chem|NH|4}}Cl + 20 {{chem|NH|3}} + {{chem|O|2}} → 4 {{chem|[|Co|(|NH|3|)|6|]|Cl|3}} + 26 {{chem|H|2|O}}
Similar reactions occur with other [[amine]]s.  These reactions are often performed in the presence of [[carbon|charcoal]] as a catalyst, or with [[hydrogen peroxide]] {{chem|H|2|O|2}} substituted for atmospheric oxygen. Other highly basic ligands, including [[carbonate]], [[acetylacetone|acetylacetonate]], and [[oxalate]], induce the formation of Co(III) derivatives. Simple carboxylates and halides do not.{{cn|date=September 2023}}

Unlike Co(II) [[Complex (chemistry)|complexes]], Co(III) complexes are very slow to exchange [[ligand]]s, 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 [[Complex (chemistry)|coordination compounds]].{{cn|date=September 2023}}

===Oxidation to cobalt(IV)===
Reaction of 1-norbornyllithium with the {{chem|CoCl|2}}·THF in pentane produces the brown, thermally stable [[tetrakis(1-norbornyl)cobalt(IV)]]<ref>{{cite journal|author = Barton K. Bower|author2 = Howard G. Tennent|name-list-style = amp|title = Transition metal bicyclo[2.2.1]hept-1-yls|journal = [[J. Am. Chem. Soc.]]|year = 1972|volume = 94|issue = 7|pages = 2512–2514|doi = 10.1021/ja00762a056}}</ref><ref>{{cite journal|journal = [[J. Chem. Soc., Chem. Commun.]]|year = 1986|issue = 19|pages = 1491–1492|doi = 10.1039/C39860001491|title = Tetrakis(1-norbornyl)cobalt, a low spin tetrahedral complex of a first row transition metal|author = Erin K. Byrne|author2 = Darrin S. Richeson|author3 = Klaus H. Theopold|name-list-style = amp}}</ref> — a rare example of a stable transition metal/saturated alkane compound,<ref name="g&e" /> different products are obtained in other solvents.<ref>{{cite journal |title = Synthesis, characterization, and electron-transfer reactivity of norbornyl complexes of cobalt in unusually high oxidation states|author = Erin K. Byrne|author2 = Klaus H. Theopold|journal = [[J. Am. Chem. Soc.]]|year = 1989|volume = 111|issue = 11|pages = 3887–3896|doi = 10.1021/ja00193a021}}</ref>