Trimagnesium 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.

This article is about Magnesium phosphate tribasic. For other uses, see magnesium phosphate.
Trimagnesium phosphate
Names
IUPAC name
Trimagnesium diphosphate
Other names
magnesium phosphate, phosphoric acid, magnesium salt (2:3), tertiary magnesium phosphate, trimagnesium phosphate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.028.931
EC Number
  • 231-824-0
E number E343 (antioxidants, ...)
15662
UNII
  • 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
  • [O-]P(=O)([O-])[O-].[O-]P(=O)([O-])[O-].[Mg+2].[Mg+2].[Mg+2]
Properties
Mg3O8P2
Molar mass 262.855 g·mol−1
Appearance White crystalline powder
Melting point 1,184 °C (2,163 °F; 1,457 K)
Insoluble
1.04×10−24
Solubility Soluble in salt solution
−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.

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.

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