Article · Wikipedia archive · Last revised Jul 27, 2026

Trimagnesium phosphate

Trimagnesium phosphate describes inorganic compounds with formula Mg3(PO4)2·nH2O. They are magnesium acid salts of phosphoric acid, with varying amounts of water of crystallization: n = 0, 5, 8, 22.

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Jul 27, 2026
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Trimagnesium phosphate
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Names
IUPAC name
Trimagnesium diphosphate
Other names
magnesium phosphate, phosphoric acid, magnesium salt (2:3), tertiary magnesium phosphate, trimagnesium phosphate
Identifiers
3D model (JSmol)
ChEBI
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
1.04×10−241
Solubility Soluble in salt solution
−167·10−6 cm3/mol (+4 H2O)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
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1
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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).

Trimagnesium phosphate describes inorganic compounds with formula Mg3(PO4)2·nH2O. They are magnesium acid salts of phosphoric acid, with varying amounts of water of crystallization: n = 0, 5, 8, 22.2

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

See also

References

References

  1. John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–188. ISBN 978-1138561632.
  2. Klaus Schrödter; Gerhard Bettermann; Thomas Staffel; Friedrich Wahl; Thomas Klein; Thomas Hofmann (2008). "Phosphoric acid and phosphates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. ISBN 978-3527306732. S2CID 94458523.
  3. "Magnesium phosphate – Compound summary". Retrieved 29 May 2012.
  4. Nord, A. G.; Stefanidis, T. (1983). "Structure of cobalt(II) phosphate structure refinements of Co3(PO4)2. A note on the reliability of powder diffraction studies". Acta Chemica Scandinavica A. 37: 715–p721. doi:10.3891/acta.chem.scand.37a-0715 (inactive 9 September 2025).{{cite journal}}: CS1 maint: DOI inactive as of September 2025 (link)
  5. "Trimagnesium phosphate". Retrieved 29 May 2012.