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 Y

3D model (JSmol)

* Interactive image

ChemSpider |

* 8305419 Y

EC Number |

* 244-166-4

PubChem CID

* 10129900

UNII |

* 51B9AYG60K Y

UN number | 3550

InChI

* InChI=1S/Co.2H2O/h;2*1H2/q+2;;/p-2 Y

Key: ASKVAEGIVYSGNY-UHFFFAOYSA-L Y

* InChI=1/Co.2H2O/h;2*1H2/q+2;;/p-2

Key: ASKVAEGIVYSGNY-NUQVWONBAS

SMILES

* [Co+2].[OH-].[OH-]

Properties

Chemical formula

| Co(OH)2
Molar mass | 92.948 g/mol
Appearance  | rose-red powder or bluish-green powder
Density | 3.597 g/cm3
Melting point |  168 °C (334 °F; 441 K) (decomposes)[1]

Solubility in water

| 3.20 mg/L

Solubility product (Ksp)

| 1.0×10−15
Solubility | soluble in acids, ammonia; insoluble in dilute alkalis
Structure

Coordination geometry

| rhombohedral
Thermochemistry

Std molar
entropy (S ~~o~~ 298)

| 79.0 J·mol−1·K−1[1]

Std enthalpy of
formation (ΔfH⦵298)

| -539.7 kJ·mol−1
Hazards
Safety data sheet | Oxford University
GHS pictograms |
GHS Signal word | Warning

GHS hazard statements

| H302, H317, H319, H330, H334, H360, H372

GHS precautionary statements

| P201, P202, P260, P261, P264, P270, P271, P272, P280, P281, P284, P285, P301+312, P302+352, P304+340, P304+341, P305+351+338, P308+313, P310, P314, P320, P321, P330, P333+313, P337+313
NFPA 704 (fire diamond)  |

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 [77 °F], 100 kPa).

Y verify (what is YN ?)
Infobox references

Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula Co(OH)2, consisting of divalent cobalt cations Co2+ and hydroxide anions OH−. The pure compound, often called the "beta form" (β-Co(OH)2) is a pink solid insoluble in water.[2][3]

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.[2][3]

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.

## Contents

* 1 Preparation
* 2 Reactions
* 3 Structure
* 3.1 Alpha form
* 3.2 Nanotubes
* 4 References

## Preparation

Cobalt(II) hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of Co2+ salt.[4] 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 N(C2H5)3 as both the base and a complexing agent.[3] It can also be prepared by elecrolysis of a solution of cobalt nitrate with a platinum cathode.[5]

## Reactions

Cobalt(II) hydroxide decomposes to cobalt(II) oxide at 168 °C under vacuum and is oxidized by air.[4] The thermal decomposition product in air above 300 °C is Co3O4.[6][7]

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−.[8]

## Structure

The pure (β) form of cobalt(II) hydroxide has the brucite crystal structure. As such, the anion and cation packing are like those in cadmium iodide, in which the cobalt(II) cations have octahedral molecular geometry.[8]

The beta form can be obtained as platelets with partial hexagonal geometry, 100-300 nm wide and 5-10 nm thick.[5][3]

### 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).[3] 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.[9]

### Nanotubes

Cobalt hydroxide can be obtained in the form of nanotubes, which may be of interest in nanotechnology and materials science. [10]

Cobalt hydroxide nanotubes. Scale bars: (a,b) 500 nm, inset 200 nm; (c,e) 50 nm; (d) 100 nm.

## References

1. ↑ 1.0 1.1 Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. p. 513. ISBN 0-8493-0594-2.
2. ↑ 2.0 2.1 Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. p. 454. ISBN 0-8493-0594-2.
3. ↑ 3.0 3.1 3.2 3.3 3.4 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. ↑ 4.0 4.1 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. ↑ 5.0 5.1 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. ↑ 8.0 8.1 Wiberg, Nils; Wiberg, Egon; Holleman, A. F. (2001). Inorganic Chemistry. Academic Press. pp. 1478–1479. ISBN 0-12-352651-5. https://books.google.com/books?id=LxhQPdMRfVIC&pg=PA1478. Retrieved 2009-03-27.
9. ↑ 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.
10. ↑ Ni, Bing; Liu, Huiling; Wang, Peng-Peng; He, Jie; Wang, Xun (2015). "General synthesis of inorganic single-walled nanotubes". Nature Communications 6: 8756. doi:10.1038/ncomms9756. PMID 26510862. Bibcode: 2015NatCo...6.8756N.

* v
* t
* e

Cobalt compounds

* CoBr2
* Co(CN)2
* CoCO3
* CoC2O4
* CoCl2
* CoCl3
* Co(ClO3)2
* CoF2
* CoF3
* CoI2
* Co(NO3)2
* Co(NO3)3
* CoO
* Co(OH)2
* CoS
* CoSO4
* CoSe
* Co2O3
* Co2P
* Co3O4
* Co3(PO4)2
* Co(Ac)2

* v
* t
* e

Hydroxides

| H2O |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | He

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LiOH | Be(OH)2 |  |  |  |  |  |  |  |  |  |  | B | C | NH3.H2O | O | F | Ne
NaOH | Mg(OH)2 |  |  |  |  |  |  |  |  |  |  | Al(OH)3 | Si | P | S | Cl | HArF (ArHF)
KOH | Ca(OH)2 | Sc(OH)3 | Ti | V | Cr(OH)2
Cr(OH)3 | Mn(OH)2 | Fe(OH)2
Fe(OH)3 | Co(OH)2 | Ni(OH)2 | CuOH
Cu(OH)2 | Zn(OH)2 | Ga(OH)3 | Ge(OH)2 | As | Se | Br | Kr
RbOH | Sr(OH)2 | Y(OH)3 | Zr(OH)4 | Nb | Mo | Tc | Ru | Rh | Pd | AgOH | Cd(OH)2 | In(OH)3 | Sn(OH)2
Sn(OH)4 | Sb(OH)3 | Te | I | Xe
CsOH | Ba(OH)2 | *  | Hf | Ta | W | Re | Os | Ir | Pt | Au(OH)3 | Hg(OH)2 | TlOH
Tl(OH)3 | Pb(OH)2
Pb(OH)4 | Bi(OH)3 | Po | At | Rn
Fr | Ra | **  | Rf | Db | Sg | Bh | Hs | Mt | Ds | Rg | Cn | Nh | Fl | Mc | Lv | Ts | Og |  |  |  |  |  |  |  |
|  | ↓ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| * | La(OH)3 | Ce(OH)3 | Pr(OH)3 | Nd(OH)3 | Pm(OH)3 | Sm(OH)3 | Eu(OH)3 | Gd(OH)3 | Tb(OH)3 | Dy(OH)3 | Ho(OH)3 | Er(OH)3 | Tm(OH)3 | Yb(OH)3 | Lu(OH)3 |
| ** | Ac | Th(OH)4 | Pa | UO2(OH)2 | Np | Pu | Am | Cm(OH)3 | Bk | Cf | Es | Fm | Md | No | Lr |

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*[CID]: Compound ID
*[H302]: Harmful if swallowed
*[H317]: May cause an allergic skin reaction
*[H319]: Causes serious eye irritation
*[H330]: Fatal if inhaled
*[H334]: May cause allergy or asthma symptoms of breathing difficulties if inhaled
*[H360]: May damage fertility or the unborn child
*[H372]: Causes damage to organs through prolonged or repeated exposure
*[P201]: Obtain special instructions before use
*[P202]: Do not handle until all safety precautions have been read and understood
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*[P264]: Wash … thoroughly after handling
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*[P272]: Contaminated work clothing should not be allowed out of the workplace
*[P280]: Wear protective gloves/protective clothing/eye protection/face protection
*[P281]: Use personal protective equipment as required
*[P284]: Wear respiratory protection
*[P285]: In case of inadequate ventilation wear respiratory protection
*[P301+312]: IF SWALLOWED: Call a POISON CENTER or doctor/physician if you feel unwell
*[P302+352]: IF ON SKIN: Wash with soap and water
*[P304+340]: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing
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*[P305+351+338]: IF IN EYES: Rinse continuously with water for several minutes. Remove contact lenses if present and easy to do – continue rinsing
*[P308+313]: IF exposed or concerned: Get medical advice/attention
*[P310]: Immediately call a POISON CENTER or doctor/physician
*[P314]: Get Medical advice/attention if you feel unwell
*[P320]: Specific treatment is urgent (see … on this label)
*[P321]: Specific treatment (see … on this label)
*[P330]: Rinse mouth
*[P333+313]: If skin irritation or a rash occurs: Get medical advice/attention
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