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Cobalt(II) hydroxide

cobalt(II) hydroxide
Names
IUPAC name Cobalt(II) hydroxide
Other names Cobaltous hydroxide, cobalt hydroxide, β-cobalt(II) hydroxide
Identifiers
CAS Number	21041-93-0
3D model (JSmol)	Interactive image
ChemSpider	8305419
ECHA InfoCard	100.040.136
EC Number	244-166-4
PubChem CID	10129900
UNII	51B9AYG60K
UN number	3550
CompTox Dashboard (EPA)	DTXSID70894155
InChI InChI=1S/Co.2H2O/h;2*1H2/q+2;;/p-2Key: ASKVAEGIVYSGNY-UHFFFAOYSA-L InChI=1/Co.2H2O/h;2*1H2/q+2;;/p-2Key: ASKVAEGIVYSGNY-NUQVWONBAS
SMILES ..
Properties
Chemical formula	Co(OH)2
Molar mass	92.948 g/mol
Appearance	rose-red powder or bluish-green powder
Density	3.597 g/cm
Melting point	168 °C (334 °F; 441 K) (decomposes)
Solubility in water	3.20 mg/L
Solubility product (Ksp)	1.0×10
Solubility	soluble in acids, ammonia; insoluble in dilute alkalis
Structure
Coordination geometry	rhombohedral
Thermochemistry
Std molar entropy (S298)	79.0 J·mol·K
Std enthalpy of formation (ΔfH298)	-539.7 kJ·mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H317, H319, H330, H334, H360, H372
Precautionary statements	P201, P202, P260, P261, P264, P270, P271, P272, P280, P281, P284, P285, P301+P312, P302+P352, P304+P340, P304+P341, P305+P351+P338, P308+P313, P310, P314, P320, P321, P330, P333+P313, P337+P313, P342+P311, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	1 0 2
Safety data sheet (SDS)	Oxford University
Related compounds
Other anions	Cobalt(II) chloride Cobalt(II) bromide Cobalt(II) iodide
Other cations	Iron(II) hydroxide Nickel(II) hydroxide Copper(II) hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula Co(OH)
₂, consisting of divalent cobalt cations Co
and hydroxide anions OH
. The pure compound, often called the "beta form" (β-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-Co(OH)
₂), which incorporates other anions in its molecular structure. This compound is blue and rather unstable.

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 Co salt. For example,

Co + 2 NaOH → Co(OH)₂ + 2 Na

The compound can be prepared by reacting cobalt(II) nitrate in water with a solution of triethylamine N(C
₂H
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.

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.

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, and .

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. 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.

The beta form can be obtained as platelets with partial hexagonal geometry, 100-300 nm wide and 5-10 nm thick.

Alpha form

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.

Nanotubes

Cobalt hydroxide can be obtained in the form of nanotubes, which may be of interest in nanotechnology and materials science.

References

1. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. p. 513. ISBN 0-8493-0594-2.
2. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. p. 454. ISBN 0-8493-0594-2.
3. ^ 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
4. ^ 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.
5. ^ 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
6. Jayashree, R. S.; Kamath, P. Vishnu (1999). "Electrochemical synthesis of a-cobalt hydroxide". Journal of Materials Chemistry. 9 (4): 961–963. doi:10.1039/A807000H.
7. Xu, Z. P.; Zeng, H. C. (1998). "Thermal evolution of cobalt hydroxides: a comparative study of their various structural phases". Journal of Materials Chemistry. 8 (11): 2499–2506. doi:10.1039/A804767G.
8. ^ Wiberg, Nils; Wiberg, Egon; Holleman, A. F. (2001). Inorganic Chemistry. Academic Press. pp. 1478–1479. ISBN 0-12-352651-5. Retrieved 2009-03-27.
9. Lutz, H.D.; Möller, H.; Schmidt, M. (1994). "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". Journal of Molecular Structure. 328: 121–132. doi:10.1016/0022-2860(94)08355-x.
10. Liu, Zhaoping; Ma, Renzhi; Osada, Minoru; Takada, Kazunori; Sasaki, Takayoshi (2005). "Selective and Controlled Synthesis of α- and β-Cobalt Hydroxides in Highly Developed Hexagonal Platelets". Journal of the American Chemical Society. 127 (40): 13869–13874. doi:10.1021/ja0523338. PMID 16201808.
11. Ni, Bing; Liu, Huiling; Wang, Peng-Peng; He, Jie; Wang, Xun (2015). "General synthesis of inorganic single-walled nanotubes". Nature Communications. 6: 8756. Bibcode:2015NatCo...6.8756N. doi:10.1038/ncomms9756. PMC 4640082. PMID 26510862.

• Cobalt(II) compounds
• Hydroxides