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. Thin films of this material are water oxidation catalysts.
A swatch of cobalt violet, popular among the French impressionists.
Preparation and structure
The tetrahydrate Co3(PO4)2•4H2O precipitates as a solid upon mixing aqueous solutions of cobalt(II) and phosphate salts. 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.