Triphosphorus pentanitride

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Triphosphorus pentanitride
IUPAC name
Triphosphorus pentanitride
Other names
Phosphorus(V) nitride, Phosphorus nitride
ECHA InfoCard 100.032.018
Molar mass 162.955
Appearance White solid
Density α-P3N5 = 2.77 g/cm3
Melting point decomposes at ≥ 850 °C (1,560 °F; 1,120 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Triphosphorus pentanitride is an inorganic compound with the chemical formula P3N5. Containing only phosphorus and nitrogen, this material is classified as a binary nitride. No applications have been developed for this material, which remains a topic of research. It is a white solid, although samples often appear colored owing to impurities.


Triphosphorus pentanitride can be produced by reactions between various phosphorus(V) and nitrogen compounds (such as ammonia and sodium azide);[1] including a reaction between the elements.[2]

3 PCl5 + 5 NH3 → P3N5 + 15 HCl
3 PCl5 + 15 NaN3 → P3N5 + 15 NaCl + 5 N2

Similar methods are used to prepared boron nitride (BN) and silicon nitride (Si3N4); however the products are generally impure and amorphous.[1][3]

Crystalline samples have been produced by the reaction of ammonium chloride and hexachlorocyclotriphosphazene:[4] or phosphorus pentachloride.[1]

(NPCl2)3 + 2 NH4Cl → P3N5 + 8 HCl
3 PCl5 + 5 NH4Cl → P3N5 + 20 HCl

P3N5 has also been prepared at room temperature, by a reaction between phosphorus trichloride and sodium amide.[5]

3 PCl3 + 5 NaNH2 → P3N5 + 5 NaCl + 4 HCl + 3 H2


P3N5 is thermally less stable than either BN or Si3N4, with decomposition to the elements occurring at temperatures above 850 °C:[1]

2 P3N5 → 6 PN + 2 N2
4 PN → P4 + 2 N2

It is resistant to weak acids and bases, and insoluble in water at room temperature, however it hydrolyzes upon heating to form the ammonium phosphate salts (NH4)2HPO4 and NH4H2PO4.

Triphosphorus pentanitride reacts with lithium nitride and calcium nitride to form the corresponding salts of PN47− and PN34−. Heterogenous ammonolyses of triphosphorus pentanitride gives imides such as HPN2 and HP4N7. It has been suggested that these compounds may have applications as solid electrolytes and pigments.[6]

Structure and properties[edit]

Several different polymorphs are known for triphosphorus pentanitride. The alpha‑form of triphosphorus pentanitride (α‑P3N5) is encountered at atmospheric pressure and exists at pressures up to 6 GPa, at which point it converts to the gamma‑variety (γ‑P3N5) of the compound. Computational chemistry indicates that a third, delta‑variety (δ‑P3N5), will form at around 43 GPa with a Kyanite-like structure.[7]

Polymorph Density (g/cm3)
α‑P3N5 2.77
γ‑P3N5 3.65
δ‑P3N5 4.02

The structure of α‑P3N5 has been determined by single crystal X-ray diffraction, which showed a network structure of edge‑sharing PN4 tetrahedra.[8]


Triphosphorus pentanitride currently has no large scale applications although it had found use as a gettering material for incandescent lamps; replacing various mixtures containing red phosphorus in the late 1960s. The lighting filaments are dipped into a suspension of P3N5 prior to being sealed into the bulb. After bulb closure, but whilst still on the pump, the lamps are lit, causing the P3N5 to thermally decompose into its constituent elements. Much of this is removed by the pump but enough P4 vapor remains to react with any residual oxygen inside the bulb. Once the vapor pressure of P4 is low enough either filler gas is admitted to the bulb prior to sealing off or, if a vacuum atmosphere is desired the bulb is sealed off at that point. The high decomposition temperature of P3N5 allows sealing machines to run faster and hotter than was possible using red phosphorus.

Related halogen containing polymers, trimeric bromophosphonitrile, (PNBr2)3, m.p. 192 °C and tetrameric bromophosphonitrile, (PNBr2)4, m.p. 202 °C find similar lamp gettering applications for tungsten halogen lamps, where they perform the dual processies of gettering and precise halogen dosing. [9]

It has also been investigated as a new material for semiconductor based electronics; particularly as a gate insulator in metal-insulator-semiconductor devices.[10][11]

Several patents have been filed for the use of triphosphorus pentanitride in fire fighting measures.[12][13]

See also[edit]


  1. ^ a b c d Schnick, Wolfgang (1 June 1993). "Solid-State Chemistry with Nonmetal Nitrides". Angewandte Chemie International Edition in English. 32 (6): 806–818. doi:10.1002/anie.199308061. 
  2. ^ Vepřek, S.; Iqbal, Z.; Brunner, J.; Schärli, M. (1 March 1981). "Preparation and properties of amorphous phosphorus nitride prepared in a low-pressure plasma". Philosophical Magazine Part B. 43 (3): 527–547. doi:10.1080/01418638108222114. 
  3. ^ Meng, Zhaoyu; Peng, Yiya; Yang, Zhiping; Qian, Yitai (1 January 2000). "Synthesis and Characterization of Amorphous Phosphorus Nitride.". Chemistry Letters (11): 1252–1253. doi:10.1246/cl.2000.1252. 
  4. ^ Schnick, Wolfgang; Lücke, Jan; Krumeich, Frank (1996). "Phosphorus Nitride P3N5: Synthesis, Spectroscopic, and Electron Microscopic Investigations". Chemistry of Materials. 8: 281. doi:10.1021/cm950385y. 
  5. ^ Chen, Luyang; Gu, Yunle; Shi, Liang; Yang, Zeheng; Ma, Jianhua; Qian, Yitai (2004). "Room temperature route to phosphorus nitride hollow spheres". Inorganic Chemistry Communications. 7 (5): 643. doi:10.1016/j.inoche.2004.03.009. 
  6. ^ Schnick, Wolfgang (1993). "Phosphorus(V) Nitrides: Preparation, Properties, and Possible Applications of New Solid State Materials with Structural Analogies to Phosphates and Silicates". Phosphorus, Sulfur, and Silicon and the Related Elements. 76 (1-4): 183–186. doi:10.1080/10426509308032389. 
  7. ^ Kroll, P; Schnick, W (2002). "A density functional study of phosphorus nitride P3N5: Refined geometries, properties, and relative stability of alpha-P3N5 and gamma-P3N5 and a further possible high-pressure phase delta-P3N5 with kyanite-type structure". Chemistry. 8 (15): 3530–7. PMID 12203333. doi:10.1002/1521-3765(20020802)8:15<3530::AID-CHEM3530>3.0.CO;2-6. 
  8. ^ Horstmann, Stefan; Irran, Elisabeth; Schnick, Wolfgang (1997). "Synthesis and Crystal Structure of Phosphorus(V) Nitrideα-P3N5". Angewandte Chemie International Edition in English. 36 (17): 1873–1875. doi:10.1002/anie.199718731. 
  9. ^ S.T. Henderson and A.M. Marsden, Lamps and Lighting 2nd Ed., Edward Arnlold Press, 1975, ISBN 0 7131 3267 1
  10. ^ Hirota, Yukihiro (1982). "Chemical vapor deposition and characterization of phosphorus nitride (P3N5) gate insulators for InP metal-insulator-semiconductor devices". Journal of Applied Physics. 53 (7): 5037. doi:10.1063/1.331380. 
  11. ^ Jeong, Yoon-Ha; Choi, Ki-Hwan; Jo, Seong-Kue; Kang, Bongkoo (1995). "Effects of Sulfide Passivation on the Performance of GaAs MISFETs with Photo-CVD Grown P3N5 Gate Insulators". Japanese Journal of Applied Physics. 34 (Part 1, No. 2B): 1176–1180. doi:10.1143/JJAP.34.1176. 
  12. ^ Phosphorus nitride agents to protect against fires and explosions, retrieved 2013  Check date values in: |access-date= (help)
  13. ^ Manufacture of flame-retardant regenerated cellulose fibres, December 20, 1977, retrieved 2013  Check date values in: |access-date= (help)