Trimagnesium phosphate

{{Short description|Inorganic compound: Mg₃(PO₄)₂·nH₂O}}

{{About|Magnesium phosphate tribasic||magnesium phosphate}}

{{Chembox

| verifiedrevid =

| ImageFile = Magnesium_phosphate_tribasic.png

| ImageFile2 = Fosforečnan hořečnatý.PNG

| ImageFile3 = EntryWithCollCode38260.png

| IUPACName = Trimagnesium diphosphate

| OtherNames = magnesium phosphate, phosphoric acid, magnesium salt (2:3), tertiary magnesium phosphate, trimagnesium phosphate

|Section1={{Chembox Identifiers

| CASNo_Ref =

| CASNo = 7757-87-1

| ChemSpiderID = 22847

| EC_number = 231-824-0

| Gmelin = 15662

| PubChem = 24439

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 453COF7817

| SMILES = [O-]P(=O)([O-])[O-].[O-]P(=O)([O-])[O-].[Mg+2].[Mg+2].[Mg+2]

| InChI = 1S/3Mg.2H3O4P/c;;;2*1-5(2,3)4/h;;;2*(H3,1,2,3,4)/q3*+2;;/p-6

| StdInChIKey = GVALZJMUIHGIMD-UHFFFAOYSA-H

}}

|Section2={{Chembox Properties

| Mg=3 | P=2 | O=8

| Appearance = White crystalline powder

| Density =

| MeltingPtC = 1184

| BoilingPt =

| Solubility = Insoluble

| SolubleOther = Soluble in salt solution

| SolubilityProduct = 1.04{{e|−24}}{{cite book |author1=John Rumble |title=CRC Handbook of Chemistry and Physics |date=June 18, 2018 |publisher=CRC Press |isbn=978-1138561632 |pages=5–188|edition=99 |language=English}}

| MagSus = −167·10⁻⁶ cm³/mol (+4 H₂O)

}}

|Section3={{Chembox Hazards

| MainHazards =

| NFPA-H = 1

| NFPA-F = 0

| NFPA-R = 0

| NFPA-S =

| FlashPt = N/A

| AutoignitionPtC = }}

}}

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.{{cite book|author1=Klaus Schrödter|chapter=Phosphoric acid and phosphates|author2=Gerhard Bettermann|author3=Thomas Staffel|author4=Friedrich Wahl|author5=Thomas Klein|author6=Thomas Hofmann|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2008|publisher=Wiley-VCH|place=Weinheim|doi=10.1002/14356007.a19_465.pub3|isbn=978-3527306732|s2cid=94458523 }}

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

: {{Chem2|Mg(H2PO4)2 · 4H2O + 2 Mg(OH)2 → Mg3(PO4)2 · 8H2O}}

The octahydrate is found in nature as the mineral bobierrite.{{cite web|title=Magnesium phosphate – Compound summary|url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=24439&loc=ec_rcs#top|accessdate=29 May 2012}}

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.{{cite journal|title=Structure of cobalt(II) phosphate structure refinements of Co₃(PO₄)₂. A note on the reliability of powder diffraction studies|author1=Nord, A. G. |author2=Stefanidis, T. |journal=Acta Chemica Scandinavica A|year=1983|volume=37|pages=715–p721|doi=10.3891/acta.chem.scand.37a-0715|doi-access=free}}