Cobalt(II) hydroxide
{{chembox
| Watchedfields = changed
| verifiedrevid = 412150315
| Name = Cobalt(II) hydroxide
| ImageFile =
| ImageSize =
| ImageCaption =
| ImageFile2 = Red cobalt hydroxide.JPG
| ImageSize2 =
| ImageCaption2 = cobalt(II) hydroxide
| IUPACName = Cobalt(II) hydroxide
| OtherNames = Cobaltous hydroxide, cobalt hydroxide, β-cobalt(II) hydroxide
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 8305419
| InChI = 1/Co.2H2O/h;2*1H2/q+2;;/p-2
| SMILES = [Co+2].[OH-].[OH-]
| InChIKey = ASKVAEGIVYSGNY-NUQVWONBAS
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Co.2H2O/h;2*1H2/q+2;;/p-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = ASKVAEGIVYSGNY-UHFFFAOYSA-L
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 21041-93-0
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 51B9AYG60K
| PubChem = 10129900
| RTECS =
| UNNumber = 3550
| EINECS = 244-166-4
}}
| Section2 = {{Chembox Properties
| Formula = Co(OH)2
| MolarMass = 92.9468 g/mol
| Appearance = rose-red powder or bluish-green powder
| Density = 3.597 g/cm3
| Solubility = 3.20 mg/L
| SolubleOther = soluble in acids, ammonia; insoluble in dilute alkalis
| SolubilityProduct = 1.0{{e|-15}}
| MeltingPtC = 168
| MeltingPt_notes = (decomposes)
| BoilingPt =
}}
| Section3 = {{Chembox Structure
| MolShape =
| Coordination = rhombohedral
| CrystalStruct =
| Dipole =
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| Section4 = {{Chembox Thermochemistry
| DeltaHf = −539.7 kJ·mol−1
| DeltaHc =
{{Cite book
| last = Lide
| first = David R.
| year = 1998
| title = Handbook of Chemistry and Physics
| edition = 87
| publication-place = Boca Raton, Florida
| publisher = CRC Press
| isbn = 0-8493-0594-2
| page = 513
}}
| HeatCapacity =
}}
| Section7 = {{Chembox Hazards
| ExternalSDS = [http://msds.chem.ox.ac.uk/CO/cobalt_II_hydroxide.html Oxford University]
| GHSPictograms = {{GHS06}}{{GHS07}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|302|317|319|330|334|360|372}}
| PPhrases = {{P-phrases|201|202|260|261|264|270|271|272|280|281|284|285|301+312|302+352|304+340|304+341|305+351+338|308+313|310|314|320|321|330|333+313|337+313|342+311|363|403+233|405|501}}
| MainHazards =
| NFPA-H = 1
| NFPA-F = 0
| NFPA-R = 2
| NFPA-S =
}}
| Section8 = {{Chembox Related
| OtherAnions = Cobalt(II) chloride
Cobalt(II) bromide
Cobalt(II) iodide
| OtherCations = Iron(II) hydroxide
Nickel(II) hydroxide
Copper(II) hydroxide
}}
}}
Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula {{chem|Co|(|OH|)|2}}, consisting of divalent cobalt cations {{chem|Co|2+}} and hydroxide anions {{chem|OH|-}}. The pure compound, often called the "beta form" (β-{{chem|Co|(|OH|)|2}}) is a pink solid insoluble in water.
The name is also applied to a related compound, often called "alpha" or "blue" form (α-{{chem|Co|(|OH|)|2}}), which incorporates other anions in its molecular structure. This compound is blue and rather unstable.{{Cite book|last = Lide|first = David R.|year = 1998|title = Handbook of Chemistry and Physics|edition = 87|publication-place = Boca Raton, Florida|publisher = CRC Press|isbn = 0-8493-0594-2|page = 454}}Xiaohe Liu, Ran Yi, Ning Zhang, Rongrong Shi, Xingguo Li, and Guanzhou Qiu (2008): "Cobalt hydroxide nanosheets and their thermal decomposition to cobalt oxide nanorings". Chemistry: An Asian Journal, volume 3, issue 4, pages 732-738. {{doi|10.1002/asia.200700264}}
Cobalt(II) hydroxide is most used as a drying agent for paints, varnishes, and inks, in the preparation of other cobalt compounds, as a catalyst and in the manufacture of battery electrodes.
Preparation
Cobalt(II) hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of Co2+ salt.O. Glemser "Cobalt(II) Hydroxide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1521. For example,
:Co2+ + 2 NaOH → Co(OH)2 + 2 Na+
The compound can be prepared by reacting cobalt(II) nitrate in water with a solution of triethylamine {{chem|N|(|C|2|H|5|)|3}} as both the base and a complexing agent. It can also be prepared by elecrolysis of a solution of cobalt nitrate with a platinum cathode.P. Benson, G. W. D. Briggs, and W. F. K. Wynne-Jones (1964): "The cobalt hydroxide electrode—I. Structure and phase transitions of the hydroxides". Electrochimica Acta, volume 9, issue 3, pages 275-280. {{doi|10.1016/0013-4686(64)80016-5}}
Reactions
Cobalt(II) hydroxide decomposes to cobalt(II) oxide at 168 °C under vacuum and is oxidized by air. The thermal decomposition product in air above 300 °C is Co3O4.{{cite journal|title=Electrochemical synthesis of a-cobalt hydroxide|author1=Jayashree, R. S. |author2=Kamath, P. Vishnu |journal=Journal of Materials Chemistry|year=1999|volume=9|issue= 4 |pages=961–963|doi=10.1039/A807000H }}{{cite journal|title=Thermal evolution of cobalt hydroxides: a comparative study of their various structural phases|author1=Xu, Z. P. |author2=Zeng, H. C. |journal=Journal of Materials Chemistry |year=1998|volume= 8|issue=11|pages=2499–2506|doi=10.1039/A804767G }}
Like iron(II) hydroxide, cobalt(II) hydroxide is a basic hydroxide, and reacts with acids to form cobalt(II) salts. It also reacts with strong bases to form solutions with dark blue cobaltate(II) anions, [Co(OH)4]2− and [Co(OH)6]4−.
Structure
The (β) form of cobalt(II) hydroxide has the brucite crystal structure, i.e. the arrangement of the atoms in the crystal are the same as the arrangement of the atoms in Mg(OH)2. The Co(II) centers are bonded to six hydroxide ligands. Each hydroxide ligand bridges to three Co(II) sites. The O-H bonds are perpendicular to the planes defined by the oxygen atoms, projecting above and below these layers.{{cite journal |doi=10.1016/0022-2860(94)08355-x |title=Lattice vibration spectra. Part LXXXII. Brucite-type hydroxides M(OH)2 (M = Ca, Mn, Co, Fe, Cd) — IR and Raman spectra, neutron diffraction of Fe(OH)2 |date=1994 |last1=Lutz |first1=H.D. |last2=Möller |first2=H. |last3=Schmidt |first3=M. |journal=Journal of Molecular Structure |volume=328 |pages=121–132 }} Ignoring the H atoms, the packing of the anion and cations is also described as the cadmium iodide structure, in which the cobalt(II) cations have octahedral molecular geometry.{{Cite book|last1 = Wiberg|first1 = Nils|last2 = Wiberg|first2 = Egon|last3 = Holleman|first3 = A. F.|year = 2001|title = Inorganic Chemistry|publisher = Academic Press|isbn = 0-12-352651-5|pages = 1478–1479|url = https://books.google.com/books?id=LxhQPdMRfVIC&pg=PA1478|accessdate = 2009-03-27}}
The beta form can be obtained as platelets with partial hexagonal geometry, 100-300 nm wide and 5-10 nm thick.
=Alpha form=
File:Alpha Cobalt Hydroxide.jpg
The so-called "alpha form" (α-Co(OH)2) is not a polymorph of the pure (β) form, but rather a more complex compound in which hydroxide-cobalt-hydroxide layers have a residual positive charge and alternate with layers of other anions such as nitrate, carbonate, chloride, etc. (the hydrotalcite structure). It is usually obtained as a blue precipitate when a base like sodium hydroxide is added to a solution of a cobalt(II) salt. The precipitate slowly converts to the beta form.{{cite journal|title=Selective and Controlled Synthesis of α- and β-Cobalt Hydroxides in Highly Developed Hexagonal Platelets|author1=Liu, Zhaoping |author2=Ma, Renzhi |author3=Osada, Minoru |author4=Takada, Kazunori |author5=Sasaki, Takayoshi |journal=Journal of the American Chemical Society|year=2005|volume=127|issue=40 |pages=13869–13874|doi=10.1021/ja0523338|pmid=16201808 }}
=Nanotubes=
Cobalt hydroxide can be obtained in the form of nanotubes, which may be of interest in nanotechnology and materials science.
References
{{Commons category|Cobalt(II) hydroxide}}
{{Reflist}}
{{Cobalt compounds}}
{{Hydroxides}}
{{DEFAULTSORT:Cobalt(II) Hydroxide}}