:Cobalt(II) chloride

At room temperature, anhydrous cobalt chloride has the cadmium chloride structure ({{chem|CdCl|2}}) (R{{overline|3}}m) in which the cobalt(II) ions are octahedrally coordinated. At about 706 °C (20 degrees below the melting point), the coordination is believed to change to tetrahedral. The vapor pressure has been reported as 7.6 mmHg at the melting point.Yuzo Saeki, Ryoko Matsuzaki, Naomi Aoyama (1977): "The vapor pressure of cobalt dichloride". Journal of the Less Common Metals, volume 55, issue 2, pages 289-291. {{doi|10.1016/0022-5088(77)90204-1}}

Cobalt chloride is fairly soluble in water. Under atmospheric pressure, the mass concentration of a saturated solution of {{chem|CoCl|2}} in water is about 54% at the boiling point, 120.2 °C; 48% at 51.25 °C; 35% at 25 °C; 33% at 0 °C; and 29% at −27.8 °C.

Diluted aqueous solutions of {{chem|CoCl|2}} contain the species {{chem|[|Co|(|H|2|O|)|6|]|2+}}, besides chloride ions. Concentrated solutions are red at room temperature but become blue at higher temperatures.The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.

The crystal unit of the solid hexahydrate {{chem|CoCl|2}}•6{{chem|H|2|O}} contains the neutral molecule trans-{{chem|CoCl|2|(|H|2|O|)|4}} and two molecules of water of crystallization.{{Wells5th}} This species dissolves readily in water and alcohol.

The anhydrous salt is hygroscopic and the hexahydrate is deliquescent.{{citation needed|date=February 2019}} The dihydrate, CoCl₂(H₂O)₂, is a coordination polymer. Each Co center is coordinated to four doubly bridging chloride ligands. The octahedron is completed by a pair of mutually trans aquo ligands.{{cite journal |title=Crystal structures of manganese(II) and iron(II) chloride dihydrate |author1=Morosin, B. |author2=Graeber, E. J. |journal=Journal of Chemical Physics |year=1965 |volume=42 |issue=3 |pages=898–901 |doi=10.1063/1.1696078 |bibcode=1965JChPh..42..898M}}

{{multiple image

| align = center

| width = 200

| footer = Structures of the forms of cobalt(II) chloride

| image1 = Cobalt(II)-chloride-3D-balls.png

| alt1 =

| caption1 = Anhydrous

| image2 = MX2(H2O)2.png

| alt2 =

| caption2 = Dihydrate

| image3 = MCl2(aq)6forFeCoNi.png

| alt3 =

| caption3 = Hexahydrate}}

Cobalt chloride can be prepared in aqueous solution from cobalt(II) hydroxide or cobalt(II) carbonate and hydrochloric acid:

:{{chem|CoCO|3}} + 2 HCl_(aq) → {{chem|CoCl|2}}_(aq) + {{chem|CO|2}} + {{chem|H|2|O}}

:{{chem|Co|(|OH|)|2}} + 2 HCl_(aq) → {{chem|CoCl|2}}_(aq) + 2{{chem|H|2|O}}

The solid dihydrate and hexahydrate can be obtained by evaporation. Cooling saturated aqueous solutions yields the dihydrate between 120.2 °C and 51.25 °C, and the hexahydrate below 51.25 °C. Water ice, rather than cobalt chloride, will crystallize from solutions with concentration below 29%. The monohydrate and the anhydrous forms can be obtained by cooling solutions only under high pressure, above 206 °C and 335 °C, respectively.

The anhydrous compound can be prepared by heating the hydrates.John Dallas Donaldson, Detmar Beyersmann, "Cobalt and Cobalt Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. {{doi|10.1002/14356007.a07_281.pub2}}

On rapid heating or in a closed container, each of the 6-, 2-, and 1- hydrates partially melts into a mixture of the next lower hydrate and a saturated solution—at 51.25 °C, 206 °C, and 335 °C, respectively. On slow heating in an open container, so that the water vapor pressure over the solid is practically zero, water evaporates out of each of the solid 6-, 2-, and 1- hydrates, leaving the next lower hydrate, at about 40°C, 89°C, and 125°C, respectively. If the partial pressure of the water vapor is in equilibrium with the solid, as in a confined but not pressurized container, the decomposition occurs at about 115°C, 145°C, and 195°C, respectively.

Dehydration can also be effected with trimethylsilyl chloride:{{cite book |chapter=Solvated and Unsolvated Anhydrous Metal Chlorides from Metal Chloride Hydrates |title=Inorganic Syntheses |volume=29 |author1=Philip Boudjouk |author2=Jeung-Ho So|pages=108–111 |doi=10.1002/9780470132609.ch26 |date=2007 |isbn=9780470132609}}

:{{chem|CoCl|2}}•6{{chem|H|2|O}} + 12 {{chem|(|CH|3|)|3|SiCl}} → {{chem|CoCl|2}} + 6{{chem|[|(|CH|3|)|3|SiCl|]|2|O}} + 12 HCl

The anhydrous compound can be purified by sublimation in vacuum.{{cite journal |author1=Wojakowska, A. |author2=Krzyżak, E. |author3=Plińska, S. |date=2007 |title=Melting and high-temperature solid state transitions in cobalt(II) halides |journal=Journal of Thermal Analysis and Calorimetry |volume=88 |issue=2 |pages=525–530 |doi=10.1007/s10973-006-8000-9}}

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}}

The hexahydrate and the anhydrous salt are weak Lewis acids. The adducts are usually either octahedral or tetrahedral. It forms an octahedral complex with pyridine ({{chem|C|5|H|5|N}}):{{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}}

:{{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 CoCl₄²⁻ can be prepared using tetraethylammonium chloride:{{cite book|author = Gill, N. S.|author2 = Taylor, F. B.| title=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}}

:{{chem|CoCl|2}} + 2 [(C₂H₅)₄N]Cl → [(C₂H₅)₄N)]₂[CoCl₄]

The tetrachlorocobaltate ion [CoCl₄]²⁻ is the blue ion that forms upon addition of hydrochloric acid to aqueous solutions of hydrated cobalt chloride, which are pink.

File:Co(norbornyl)4.png 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 cobaltocenium cation {{chem|[|Co|(|C|5|H|5|)|2|]|+}}.

Compounds of cobalt in the +3 oxidation state exist, such as cobalt(III) fluoride {{chem|CoF|3}}, nitrate {{chem|Co|(|NO|3|)|3}}, and 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.Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.

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 amines. For example, in the presence of ammonia, cobalt(II) chloride is readily 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 amines. These reactions are often performed in the presence of charcoal as a catalyst, or with hydrogen peroxide {{chem|H|2|O|2}} substituted for atmospheric oxygen. Other highly basic ligands, including carbonate, acetylacetonate, and oxalate, induce the formation of Co(III) derivatives. Simple carboxylates and halides do not.{{cn|date=September 2023}}

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.{{cn|date=September 2023}}

Reaction of 1-norbornyllithium with the {{chem|CoCl|2}}·THF in pentane produces the brown, thermally stable tetrakis(1-norbornyl)cobalt(IV){{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}}{{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}} — a rare example of a stable transition metal/saturated alkane compound, different products are obtained in other solvents.{{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}}

File:Blue silica gel.jpg is due to cobalt chloride. When hydrated the colour changes to a light pink/purple.]]

Cobalt chloride is a common visual moisture indicator due to its distinct colour change when hydrated. The colour change is from some shade of blue when dry, to a pink when hydrated, although the shade of colour depends on the substrate and concentration. It is impregnated into paper to make test strips for detecting moisture in solutions, or more slowly, in air/gas. Desiccants such as silica gel can incorporate cobalt chloride to indicate when it is "spent" (i.e. hydrated).{{Cite journal|last=Solomon|first=M. E.|date=February 1945|title=The use of cobalt salts as indicators of humidity and moisture|url=https://onlinelibrary.wiley.com/doi/10.1111/j.1744-7348.1945.tb06763.x|journal=Annals of Applied Biology|language=en|volume=32|issue=1|pages=75–85|doi=10.1111/j.1744-7348.1945.tb06763.x|issn=0003-4746}}

Cobalt is essential for most higher forms of life, but more than a few milligrams each day is harmful. Although poisonings have rarely resulted from cobalt compounds, their chronic ingestion has caused serious health problems at doses far less than the lethal dose. In 1966, the addition of cobalt compounds to stabilize beer foam in Canada led to a peculiar form of toxin-induced cardiomyopathy, which came to be known as beer drinker's cardiomyopathy.{{cite journal |author= Morin Y |author2= Tětu A |author3= Mercier G|title=Quebec beer-drinkers' cardiomyopathy: Clinical and hemodynamic aspects |journal=Annals of the New York Academy of Sciences |volume=156 |issue= 1 |pages=566–576 |date=1969|pmid=5291148 |doi=10.1111/j.1749-6632.1969.tb16751.x|bibcode = 1969NYASA.156..566M |s2cid= 7422045 }}{{cite journal|title = Cobalt|author = Barceloux, Donald G.|author2 = Barceloux, Donald|name-list-style = amp |doi = 10.1081/CLT-100102420|pmid = 10382556|journal = Clinical Toxicology|volume = 37|issue = 2|date = 1999| pages = 201–216}}[https://pubchem.ncbi.nlm.nih.gov/compound/Cobalt_sulfate#section=Human-Toxicity-Excerpts 11.1.5 The unusual type of myocardiopathy recognized in 1965 and 1966 in Quebec (Canada), Minneapolis (Minnesota), Leuven (Belgium), and Omaha (Nebraska) was associated with episodes of acute heart failure (e/g/, 50 deaths among 112 beer drinkers).]

Furthermore, cobalt(II) chloride is suspected of causing cancer (i.e., possibly carcinogenic, IARC Group 2B) as per the International Agency for Research on Cancer (IARC) Monographs.[http://publications.iarc.fr/_publications/media/download/2705/29aacee6b89ff816188dcd990b61a16ad6486eec.pdf [PDF]

In 2005–06, cobalt chloride was the eighth-most-prevalent allergen in patch tests (8.4%).Zug KA, Warshaw EM, Fowler JF Jr, Maibach HI, Belsito DL, Pratt MD, Sasseville D, Storrs FJ, Taylor JS, Mathias CG, Deleo VA, Rietschel RL, Marks J. Patch-test results of the North American Contact Dermatitis Group 2005–2006. Dermatitis. 2009 May–Jun;20(3):149-60.

• Invisible ink: when suspended in solution, cobalt(II) chloride can be made to appear invisible on a surface; when that same surface is subsequently exposed to significant heat (such as from a handheld heat gun or lighter) the ink reversibly changes to blue.{{cite web|url=https://edu.rsc.org/in-search-of-solutions/making-invisible-ink/1178.article|title=Making invisible ink|accessdate=7 April 2023 |publisher=Royal Society of Chemistry}}
• Cobalt chloride is an established chemical inducer of hypoxia-like responses such as erythropoiesis.{{citation needed|date=November 2019}} Cobalt supplementation is not banned and therefore would not be detected by current anti-doping testing.{{cite journal |pmid=16244201 |doi=10.1136/bjsm.2005.019232 |volume=39 |issue=11 |title=Cobalt chloride administration in athletes: a new perspective in blood doping? |pmc=1725077 |date=November 2005 |journal=Br J Sports Med |pages=872–873 |vauthors=Lippi G, Franchini M, Guidi GC}} Cobalt chloride is a banned substance under the Australian Thoroughbred Racing Board.{{cite news |title=Cobalt crisis turns the eyes of the world onto Australian racing |url=https://www.smh.com.au/sport/racing/cobalt-crisis-turns-the-eyes-of-the-world-onto-australian-racing-20150206-137w22.html |first=Patrick|last=Bartley|newspaper=The Sydney Morning Herald |date=6 February 2015}}
• Cobalt chloride is one method used to induce pulmonary arterial hypertension in animals for research and evaluation of treatment efficacy.

{{Reflist|2}}

{{Commons category|Cobalt(II) chloride|lcfirst=yes}}

• [http://www.inchem.org/documents/icsc/icsc/eics0783.htm International Chemical Safety Card 0783]
• [https://web.archive.org/web/20060219230038/http://www.npi.gov.au/database/substance-info/profiles/26.html National Pollutant Inventory – Cobalt fact sheet]
• [https://web.archive.org/web/20051012230942/http://www-cie.iarc.fr/htdocs/monographs/vol52/11-cobaltandcobaltcomp.htm IARC Monograph "Cobalt and Cobalt Compounds"]

{{Cobalt compounds}}

{{Chlorides}}

Category:Cobalt(II) compounds

Category:Inorganic compounds

Category:Chlorides

Category:Metal halides

Category:IARC Group 2B carcinogens

Category:Deliquescent materials