Magnesium diphosphate

Crystal structure
__ Mg 2+ __ P 5+ __ O 2−
Crystal system	monoclinic
Space group	P 2 1 / c (No. 14)
Lattice parameters	a = 13.198 Å, b = 8.259 Å, c = 13.198 Å, β = 104.9 °, Z = 2
General
Surname	Magnesium diphosphate
other names	Magnesium pyrophosphate
Ratio formula	Mg 2 P 2 O 7
Brief description	White solid
External identifiers / databases
CAS number 10102-34-8 (dihydrate) 13446-24-7 (hexahydrate) EC number 236-595-0 ECHA InfoCard 100.033.254 PubChem 122213 Wikidata Q18211724
properties
Molar mass	222.551 g mol −1
Physical state	firmly
density	3.14 g cm −3
Melting point	1395 ± 5 ° C
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 315-319-335 P: 280-302 + 352-304 + 340-312-332 + 313-337 + 313
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Magnesium diphosphate (alternatively: magnesium pyrophosphate ) is the salt of magnesium with diphosphoric acid .

presentation

Magnesium pyrophosphate can be prepared by thermal decomposition of magnesium hydrogen phosphate or magnesium ammonium phosphate .

${\displaystyle {\ce {2MgHPO4 ->[\Delta] Mg2P2O7 + H2O}}}$

${\displaystyle {\ce {2MgNH4PO4 ->[\Delta] Mg2P2O7 + 2 NH3 ^ + H2O}}}$

Alternatively, precipitation from aqueous solution is also possible, in which case the hexahydrate is obtained.

${\displaystyle {\ce {Mg^{2}+ + P2O7^{2}- + 6H2O -> Mg2P2O7.6H2O v}}}$

use

Magnesium diphosphate was used in analysis for the quantitative determination of magnesium ions in solution. Alternatively, the connection can also be used for gravimetric determination of the concentration of phosphoric acid solutions.

Magnesium diphosphate is a plant virus inhibitor and has found corresponding industrial use.

The research investigated the use of magnesium pyrophosphate doped with cerium or thorium as a fluorescent substance in the UV range.

properties

The compound is in the α-modification at room temperature. This crystallizes in the monoclinic space group P 2 ₁ / c (space group no. 14) with the lattice constants a = 13.198 Å, b = 8.259 Å, c = 13.198 Å and β = 104.9 °. There are two formula units in a unit cell. From 68 ° C a transition to the β-modification takes place, which is isostructural to β- zinc pyrophosphate and thortveitite . The space group C 2 / m (space group no. 12) has the dimensions a = 6.494 Å, b = 8.28 Å, c = 4.522 Å and β = 103.8 ° with Z = 2. The dihydrate lies in the P. 2 ₁ / n with the lattice constants a = 7.367 Å, ​​b = 13.906 Å, c = 6.277 Å and β = 94.37 ° with four units per unit cell. The hexahydrate crystallizes in the space group P 2 ₁ / n (space group no. 14, position 2) with the parameters a = 7.189 Å, b = 18.309 Å, c = 7.665 Å and β = 92.360 °. There are four formula units in a unit cell.

The absolute entropy S ₀ is 37.02 ± 0.15  cal · mol ^-1 · K ^-1 , the melting enthalpy .DELTA.H _fus is 32.1 ± 0.4 kcal · mol ^-1 . The enthalpy of the phase transition is 729 cal · mol ⁻¹

Individual evidence

1. ↑ ^{a b c} data sheet magnesium pyrophosphate at AlfaAesar, accessed on February 25, 2019 ( PDF )(JavaScript required) .
2. ↑ ^{a b} Crispin Calvo: The crystal structure of α-Mg ₂ P ₂ O ₇ . In: Acta Crystallographica . tape 23 , 1967, p. 289–295 , doi : 10.1107 / S0365110X67002610 ( Open Access ).
3. ^ ^{A b} F. L. Oetting, RA McDonald: The thermodynamic properties of magnesium orthophosphate and magnesium pyrophosphate . In: The Journal of Physical Chemistry . tape 67 , no. December 12 , 1963, p. 2737-2743 , doi : 10.1021 / j100806a055 .
4. ^ ^{A b} Richard C. Ropp: Encyclopedia of the Alkaline Earth Compounds . Newnes, 2012, ISBN 978-0-444-59553-9 , pp. 266–268 ( limited preview in Google Book Search [accessed February 25, 2019]).
5. ↑ Stanko Stankov Miholić: The pyrophosphate method for the determination of magnesium . In: Journal of the Chemical Society . 1930, p. 200-202 , doi : 10.1039 / JR9300000200 .
6. ↑ Michael Wächter: Book of tables of chemistry . Data on analysis, laboratory practice and theory. John Wiley & Sons , 2012, ISBN 978-3-527-32960-1 , pp. 78 ( limited preview in Google Book Search [accessed February 25, 2019]).
7. ↑ Herman C. Froelich: Double and triple activated magnesium pyrophosphate phosphors . In: Journal of the Electrochemical Society . tape 95 , no. 5 , May 1949, p. 254–266 , doi : 10.1149 / 1.2776753 ( psu.edu [PDF; accessed February 25, 2019]).
8. ↑ Patent US2455415A : Ultraviolet emitting magnesium pyrophosphate phosphorus. Filed April 15, 1947 , published December 7, 1948 , Applicant: General Electric, Inventor: Herman C. Froelich. ‌
9. ^ Crispin Calvo: Refinement of the crystal structure of β-Mg ₂ P ₂ O ₇ . In: Canadian Journal of Chemistry . tape 43 , no. 5 , 1965, pp. 1139-1146 , doi : 10.1139 / v65-151 .
10. ↑ J. Oka, A. Kawahara: The structure of synthetic dimagnesium diphosphate (V) dihydrate . In: Acta Crystallographica . B38, p. 3-5 , doi : 10.1107 / S0567740882001927 .
11. ↑ Mohamed Souhassou, Claude Lecomte, Robert H. Blessing: Crystal Chemistry of Mg ₂ P ₂ O ₇ , n = 0, 2 and 6 . Magnesium-Oxygen coordination and pyrophosphate ligation and conformation. In: Acta Crystallographica . B48, 1992, p. 370–376 , doi : 10.1107 / S0108768191014313 ( Open Access ).