Trimagnesium phosphate

This article is about Magnesium phosphate tribasic. For other uses, see magnesium phosphate.

Trimagnesium phosphate describes inorganic compounds with formula Mg₃(PO₄)₂^.xH₂O. They are magnesium acid salts of phosphoric acid, with varying amounts of water of crystallization: x = 0, 5, 8, 22.^[2]

Trimagnesium phosphate

Names
IUPAC name Trimagnesium diphosphate
Other names magnesium phosphate, phosphoric acid, magnesium salt (2:3), tertiary magnesium phosphate, trimagnesium phosphate
Identifiers
CAS Number	7757-87-1
3D model (JSmol)	Interactive image
ChemSpider	22847
ECHA InfoCard	100.028.931
EC Number	231-824-0
E number	E343 (antioxidants, ...)
Gmelin Reference	15662
PubChem CID	24439
UNII	453COF7817 Y
CompTox Dashboard (EPA)	DTXSID00872527
InChI Key: GVALZJMUIHGIMD-UHFFFAOYSA-H InChI=1S/3Mg.2H3O4P/c;;;2*1-5(2,3)4/h;;;2*(H3,1,2,3,4)/q3*+2;;/p-6
SMILES [O-]P(=O)([O-])[O-].[O-]P(=O)([O-])[O-].[Mg+2].[Mg+2].[Mg+2]
Properties
Chemical formula	Mg3O8P2
Molar mass	262.855 g·mol−1
Appearance	White crystalline powder
Melting point	1,184 °C (2,163 °F; 1,457 K)
Solubility in water	Insoluble
Solubility product (Ksp)	1.04×10−24[1]
Solubility	Soluble in salt solution
Magnetic susceptibility (χ)	−167·10−6 cm3/mol (+4 H2O)
Hazards
NFPA 704 (fire diamond)	1 0 0
Flash point	N/A
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The octahydrate forms upon reaction of stoichiometric quantities of monomagnesium phosphate (tetrahydrate) with magnesium hydroxide.

Mg(H₂PO₄)₂•4H₂O + 2 Mg(OH)₂ → Mg₃(PO₄)₂•8H₂O

The octahydrate is found in nature as the mineral bobierrite.^[3]

The anhydrous compound is obtained by heating the hydrates to 400 °C. It is isostructural with cobalt(II) phosphate. The metal ions occupy both octahedral (six-coordinate) and pentacoordinate sites in a 1:2 ratio.^[4]

Safety

Magnesium phosphate tribasic is listed on the FDA's generally recognized as safe, or GRAS, list of substances.^[5]

See also

• Magnesium phosphate