Cobalt(II) hydroxide or cobaltous hydroxide is the inorganic compound with the formula , consisting of

divalent In chemistry, the valence (US spelling) or valency (British spelling) of an chemical element, element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, ...

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...

and

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

anions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

. The pure compound, often called the "beta form" (β-) is a pink solid insoluble in water. The name is also applied to a related compound, often called "alpha" or "blue" form (α-), which incorporates other anions in its molecular structure. This compound is blue and rather unstable.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. 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 Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

and in the manufacture of battery

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...

Preparation

Cobalt(II) hydroxide precipitates as a solid when an alkali metal

is added to an

aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...

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 Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

in water with a solution of

triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...

as both the base and a

complexing agent A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

. It can also be prepared by elecrolysis of a solution of cobalt nitrate with a

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

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.

Reactions

Cobalt(II) hydroxide decomposes to

cobalt(II) oxide Cobalt(II) oxide is an inorganic compound that has been described as an olive-green or gray solid. It is used extensively in the ceramics industry as an additive to create blue colored glazes and enamels as well as in the chemical industry for pr ...

at 168 °C under

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...

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, o(OH)₄sup>2− and o(OH)₆sup>4−.

Structure

The pure (β) form of cobalt(II) hydroxide has the

brucite Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg( OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and ...

crystal structure. As such, the anion and cation packing are like those in

cadmium iodide Cadmium iodide is the inorganic compound with the formula CdI2. It is a white hygroscopic solid. It also can be obtained as a mono- and tetrahydrate. It has few applications. It is notable for its crystal structure, which is typical for compoun ...

, 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 A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride sa ...

, 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. Cobalt hydroxide nanotubes

References

{{DEFAULTSORT:Cobalt(II) Hydroxide Cobalt(II) compounds Hydroxides