 cobalt(II) hydroxide | |
| Names | |
|---|---|
| IUPAC name Cobalt(II) hydroxide | |
| Other names Cobaltous hydroxide, cobalt hydroxide, β-cobalt(II) hydroxide | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
|
| ECHA InfoCard | 100.040.136 |
| EC Number |
|
| UNII | |
| UN number | 3550 |
| |
| |
| Properties | |
| Co(OH)2 | |
| Molar mass | 92.9468 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 product (Ksp) | 1.0×10−15 |
| Solubility | soluble inacids,ammonia; insoluble in dilutealkalis |
| Structure | |
| rhombohedral | |
| Thermochemistry | |
Std molar entropy(S⦵298) | 79.0 J·mol−1·K−1[1] |
Std enthalpy of formation(ΔfH⦵298) | −539.7kJ·mol−1 |
| Hazards | |
| GHS labelling: | |
    | |
| Warning | |
| H302,H317,H319,H330,H334,H360,H372 | |
| 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) | |
| Safety data sheet (SDS) | Oxford University |
| Related compounds | |
Otheranions | Cobalt(II) chloride Cobalt(II) bromide Cobalt(II) iodide |
Othercations | Iron(II) hydroxide Nickel(II) hydroxide Copper(II) hydroxide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Cobalt(II) hydroxide orcobaltous hydroxide is theinorganic compound with the formulaCo(OH)
2, consisting ofdivalentcobaltcationsCo2+
andhydroxideanionsOH−
. 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 adrying agent forpaints,varnishes, andinks, in the preparation of other cobalt compounds, as acatalyst and in the manufacture ofbatteryelectrodes.
Cobalt(II) hydroxideprecipitates as a solid when analkali metalhydroxide is added to anaqueous solution of Co2+ salt.[4] For example,
The compound can be prepared by reactingcobalt(II) nitrate in water with a solution oftriethylamineN(C
2H
5)
3 as both the base and acomplexing agent.[3] It can also be prepared by elecrolysis of a solution of cobalt nitrate with aplatinum cathode.[5]
Cobalt(II) hydroxide decomposes tocobalt(II) oxide at 168 °C undervacuum and is oxidized by air.[4] The thermal decomposition product in air above 300 °C isCo3O4.[6][7]
Likeiron(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]
The (β) form of cobalt(II) hydroxide has thebrucite 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 hydroxideligands. Each hydroxide ligandbridges 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.[9] Ignoring the H atoms, the packing of the anion and cations is also described as thecadmium iodide structure, in which the cobalt(II) cations haveoctahedral molecular geometry.[8]
The beta form can be obtained as platelets with partial hexagonal geometry, 100-300nm wide and 5-10 nm thick.[5][3]
The so-called "alpha form" (α-Co(OH)2) is not apolymorph 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 asnitrate,carbonate,chloride, etc. (thehydrotalcite structure).[3] It is usually obtained as a blue precipitate when a base likesodium hydroxide is added to a solution of a cobalt(II) salt. The precipitate slowly converts to the beta form.[10]
Cobalt hydroxide can be obtained in the form ofnanotubes, which may be of interest innanotechnology andmaterials science.[11]
