Cobalt(II) hydroxide

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Cobalt(II) hydroxide
Red cobalt hydroxide.JPG
cobalt(II) hydroxide
IUPAC name
Cobalt(II) hydroxide
Other names
Cobaltous hydroxide, cobalt hydroxide, β-cobalt(II) hydroxide
3D model (JSmol)
ECHA InfoCard 100.040.136
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]
3.20 mg/L
Solubility soluble in acids, ammonia; insoluble in dilute alkalis
79.0 J·mol−1·K−1[1]
-539.7 kJ·mol−1
Safety data sheet Oxford University
Harmful Xn
R-phrases (outdated) R20 R21 R22 R36 R37 R38 R43
S-phrases (outdated) S24 S26 S36 S37 S39[2]
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored 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).
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Infobox references

Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula Co(OH)2. It is a rose-red powder. An unstable blue form, so-called α-Co(OH)2, has also been reported.[3] It 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 and reactions[edit]

Cobalt(II) hydroxide precipitates as a solid when an alkali metal hydroxide is added to an aqueous solution of Co2+ salt:[4]

Co2+ + 2 NaOH → Co(OH)2 + 2 Na+

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.[5][6]

Like iron(II) hydroxide, cobalt(II) hydroxide is a basic hydroxide. It form [Co(H2O)6]2+ in acidic aqueous solutions. In strong bases, cobalt(II) hydroxide accepts additional hydroxide ions to form dark blue cobaltates(II) [Co(OH)4]2− and [Co(OH)6]4−.[7]


Cobalt(II) hydroxide has the brucite crystal structure. As such, the anion and cation packing are like those in cadmium iodide. Cadmium has octahedral molecular geometry.[7] The so-called α-Co(OH)2 is related closely to β-Co(OH)2 but adopts the hydrotalcite structure. As such it contains anions in the interlayers, hence it is not a polymorph. α-Co(OH)2 is a precursor to β-Co(OH)2.[8]

Cobalt hydroxide nanotubes. Scale bars: (a,b) 500 nm, inset 200  nm; (c,e) 50 nm; (d) 100  nm.[9]


  1. ^ a b Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. p. 513. ISBN 0-8493-0594-2. 
  2. ^ "Safety (MSDS) data for cobalt (II) hydroxide". Oxford University. Retrieved 2009-03-27. 
  3. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. p. 454. ISBN 0-8493-0594-2. 
  4. ^ a b 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. ^ 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. 
  6. ^ 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. 
  7. ^ a b Wiberg, Nils; Wiberg, Egon; Holleman, A. F. (2001). Inorganic Chemistry. Academic Press. pp. 1478–1479. ISBN 0-12-352651-5. Retrieved 2009-03-27. 
  8. ^ 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: 13869–13874. doi:10.1021/ja0523338. 
  9. ^ Ni, Bing; Liu, Huiling; Wang, Peng-Peng; He, Jie; Wang, Xun (2015). "General synthesis of inorganic single-walled nanotubes". Nature Communications. 6: 8756. PMC 4640082Freely accessible. PMID 26510862. doi:10.1038/ncomms9756.