Triphosphorus pentanitride is an inorganic compound with the chemical formulaP3N5. Containing only phosphorus and nitrogen, this material is classified as a binarynitride. While it has been investigated for various applications this has not led to any significant industrial uses. It is a white solid, although samples often appear colored owing to impurities.
Synthesis
Triphosphorus pentanitride can be produced by reactions between various phosphorus(V) and nitrogen anions (such as ammonia and sodium azide):[1]
3 PCl5 + 5 NH3 → P3N5 + 15 HCl
3 PCl5 + 15 NaN3 → P3N5 + 15 NaCl + 20 N2
The reaction of the elements is claimed to produce a related material.[2] Similar methods are used to prepared boron nitride (BN) and silicon nitride (Si3N4); however the products are generally impure and amorphous.[1][3]
P3N5 is thermally less stable than either BN or Si3N4, with decomposition to the elements occurring at temperatures above 850 °C:[1]
P3N5 → 3 PN + 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 [NH4]H2PO4.
Triphosphorus pentanitride reacts with lithium nitride and calcium nitride to form the corresponding salts of PN7−4 and PN4−3. 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
Several 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 11 GPa, at which point it converts to the gamma‑variety (γ‑P3N5) of the compound.[7][8] Upon heating γ‑P3N5 to temperatures above 2000 K at pressures between 67 and 70 GPa, it transforms into δ-P3N5.[9] The release of pressure on the δ-P3N5 polymorph does not revert it back into γ‑P3N5 or α‑P3N5. Instead, at pressures below 7 GPa, δ-P3N5 converts into a fourth form of triphosphorus pentanitride, α′‑P3N5.[9]
Polymorph
Density (g/cm3)
α‑P3N5
2.77
α′‑P3N5
3.11
γ‑P3N5
3.65
δ‑P3N5
5.27 (at 72 GPa)
The structure of all polymorphs of triphosphorus pentanitride was determined by single crystalX-ray diffraction. α‑P3N5 and α′‑P3N5 are formed of a network structure of PN4 tetrahedra with 2- and 3-coordinated nitrides,[7][9] γ‑P3N5 is composed of both PN4 and PN5 polyhedra[8] while δ-P3N5 is composed exclusively of corner- and edge-sharing PN6 octahedra.[9] δ-P3N5 is the most incompressible triphosphorus pentanitride, having a bulk modulus of 313 GPa.[9]
Potential applications
Triphosphorus pentanitride has no commercial applications, although it 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 while 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 (melting point 192 °C) and tetrameric bromophosphonitrile (PNBr2)4 (melting point 202 °C) find similar lamp gettering applications for tungsten halogen lamps, where they perform the dual processies of gettering and precise halogen dosing.[10]
As a fuel in pyrotechnic obscurant mixtures, it offers some benefits over the more commonly used red phosphorus, owing mainly to its higher chemical stability. Unlike red phosphorus, P3N5 can be safely mixed with strong oxidizers, even potassium chlorate. While these mixtures can burn up to 200 times faster than state-of-the-art red phosphorus mixtures, they are far less sensitive to shock and friction. Additionally, P3N5 is much more resistant to hydrolysis than red phosphorus, giving pyrotechnic mixtures based on it greater stability under long-term storage.[13]
Patents have been filed for the use of triphosphorus pentanitride in fire fighting measures.[14][15]
^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 B. 43 (3): 527–547. Bibcode:1981PMagB..43..527V. doi:10.1080/01418638108222114.
^Meng, Zhaoyu; Peng, Yiya; Yang, Zhiping; Qian, Yitai (1 January 2000). "Synthesis and Characterization of Amorphous Phosphorus Nitride". Chemistry Letters. 29 (11): 1252–1253. doi:10.1246/cl.2000.1252.
^Schnick, Wolfgang; Lücke, Jan; Krumeich, Frank (1996). "Phosphorus Nitride P3N5: Synthesis, Spectroscopic, and Electron Microscopic Investigations". Chemistry of Materials. 8: 281–286. doi:10.1021/cm950385y.
^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.
^ abHorstmann, 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.
^S.T. Henderson and A.M. Marsden, Lamps and Lighting 2nd Ed., Edward Arnlold Press, 1975, ISBN0 7131 3267 1
^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): 5037–5043. Bibcode:1982JAP....53.5037H. doi:10.1063/1.331380.
^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. Bibcode:1995JaJAP..34.1176J. doi:10.1143/JJAP.34.1176. S2CID67837168.
^Koch, Ernst-Christian; Cudziło, Stanisław (2016), "Safer Pyrotechnic Obscurants Based on Phosphorus(V) Nitride", Angewandte Chemie International Edition, 55 (49): 15439–15442, doi:10.1002/anie.201609532, PMID27862760
