Cobalt(II) phosphate

Cobalt phosphate is the inorganic compound with the formula Co₃(PO₄)₂. It is a commercial inorganic pigment known as cobalt violet.^[2] Thin films of this material are water oxidation catalysts.^[3]

A swatch of cobalt violet, popular among the French impressionists.

Cobalt(II) phosphate

Names
Other names cobalt violet, cobalt(II) phosphate, cobalt orthophosphate, Pigment Violet 14
Identifiers
CAS Number	(tetrahydrate: 10294-50-5) 13455-36-2 (tetrahydrate: 10294-50-5) Y
3D model (JSmol)	Interactive image
ChemSpider	55523
ECHA InfoCard	100.033.309
EC Number	236-655-6
PubChem CID	61615
UNII	0B5M38T47H Y
CompTox Dashboard (EPA)	DTXSID20893875
InChI InChI=1S/3Co.2H3O4P/c;;;2*1-5(2,3)4/h;;;2*(H3,1,2,3,4)/q3*+2;;/p-6 Key: ZBDSFTZNNQNSQM-UHFFFAOYSA-H InChI=1/3Co.2H3O4P/c;;;2*1-5(2,3)4/h;;;2*(H3,1,2,3,4)/q3*+2;;/p-6 Key: ZBDSFTZNNQNSQM-CYFPFDDLAU
SMILES [O-]P(=O)([O-])[O-].[O-]P(=O)([O-])[O-].[Co+2].[Co+2].[Co+2]
Properties
Chemical formula	Co3(PO4)2
Molar mass	366.74231 g/mol
Appearance	violet solid
Density	3.81 g/cm3
Melting point	1,160 °C (2,120 °F; 1,430 K)
Solubility in water	insoluble
Solubility product (Ksp)	2.05×10−35[1]
Magnetic susceptibility (χ)	28,110.0·10−6 cm3/mol
Refractive index (nD)	1.7
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation and structure

The tetrahydrate Co₃(PO₄)₂•4H₂O precipitates as a solid upon mixing aqueous solutions of cobalt(II) and phosphate salts.^[4][5] Upon heating, the tetrahydrate converts to the anhydrous material. According to X-ray crystallography, the anhydrous Co₃(PO₄)₂ consists of discrete phosphate (PO³⁻
₄) anions that link Co²⁺
centres. The cobalt ions occupy both octahedral (six-coordinate) and pentacoordinate sites in a 1:2 ratio.^[6][7]

See also

• List of inorganic pigments