Nitrogen pentafluoride

Nitrogen pentafluoride

Names
IUPAC name Nitrogen pentafluoride
Identifiers
CAS Number	13706-13-3[1]
Properties
Chemical formula	NF5
Molar mass	108.999 g/mol
Structure
Molecular shape	trigonal bipyramidal
Dipole moment	0 D
Related compounds
Other cations	Phosphorus pentafluoride Arsenic pentafluoride Antimony pentafluoride Bismuth pentafluoride
Related compounds	Nitrogen trifluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Nitrogen pentafluoride is a theoretical compound of nitrogen and fluorine that is hypothesized to exist based on the existence of the pentafluorides of the atoms below nitrogen in the periodic table, such as phosphorus pentafluoride. Theoretical models of the nitrogen pentafluoride (NF₅) molecule are either a trigonal bipyramidal covalently bound molecule with symmetry group D_3h, or NF+
4F⁻, which would be an ionic solid. Also, a related compound NH+
4F⁻ is known.^[2]

Ionic solid

In 1966 W. E. Tolberg first synthesized a five valent nitrogen compound of nitrogen and fluorine when tetrafluoroammonium compounds, tetrafluoroammonium heaxafluoroantimonate NF₄SbF₆ and tetrafluoroammonium heaxafluoroarsenate NF₄AsF₆ were made.^[3] In 1971 C. T. Goetschel announced the preparation of NF₄BF₄ and also produced a white solid assumed to be tetrafluoroammonium fluoride (NF+
4F⁻). This was made by treating nitrogen trifluoride and fluorine with 3MeV electron radiation at 77K. It decomposed above 143K back into those ingredients.^[3] Theoretical studies also show the ionic compound is very likely to decompose to nitrogen trifluoride and fluorine gas.^[4]

Karl O. Christe synthesised bis(tetrafluoroammonium) hexafluoronickelate (NF₄)₂NiF₆.^[5] He also prepared compounds with manganese, a fluorouranate, a perchlorate, a fluorosulfate and N₂F+
3 salts.^[6] Christe attempted to make NF₄F by metathesis of NF₄SbF₆ with CsF in HF solvent at 20 °C. However, a variant, tetrafluoroammonium bifluoride (NF₄HF₂·nHF), was produced. At room temperature it was a milky liquid, but when cooled turned pasty. At −45 °C it had the form of a white solid. When reheated it frothed, giving off F₂, HF and NF₃ as gases.^[6] This has CAS number 71485-49-9.^[7]

I. J. Solomon believed that nitrogen pentafluoride was produced by the thermal decomposition of NF₄AsF₆, but experimental results were not reproduced.^[8]

Dominik Kurzydłowski and Patryk Zaleski-Ejgierd predict that a mixture of fluorine and nitrogen trifluoride under pressure between 10 and 33 Gpa forms NF+
4F⁻. This is a high pressure oxidation. Over 33 GPa it will form a stable ionic compound with formula (NF+
4)₂NF−
6F^– with space group Ir/m. Over 151 GPa this is predicted to transform to NF+
4NF−
6.^[9] A NF₅ molecular compound is not stable under any pressure conditions.

Molecule

Possible structures of NF₅

For a NF₅ molecule to form, five fluorine atoms have to be arranged around a nitrogen atom. There is insufficient space to do this in the most compact way, so that bond lengths are forced to be longer. Calculations show that the NF₅ molecule is thermodynamically favourably inclined to form NF₄ and F radicals with energy 36 kJ/mol and a transition barrier around 67–84 kJ/mol.^[10] Nitrogen pentafluoride also violates the octet rule in which compounds with eight outer shell electrons are particularly stable.^[2]

References

1. F Fluorine: Compounds with Oxygen and Nitrogen. Gmelin Handbook of Inorganic Chemistry. 4. Berlin: Springer. 1986. p. 163. doi:10.1007/978-3-662-06339-2. ISBN 978-3-662-06341-5. Retrieved 29 August 2015.
2. Lewars, Errol G. (3 November 2008). "Nitrogen Pentafluoride and Related Compounds". Modeling marvels: computational anticipation of novel molecules. Springer. pp. 53–67. doi:10.1007/978-1-4020-6973-4_4. ISBN 978-1-4020-6972-7.
3. Goetschel, C. T.; V. A. Campanile; R. M. Curtis; K. R. Loos; C. D. Wagner; J. N. Wilson (July 1972). "Preparation and properties of perfluoroammonium tetrafluoroborate, NF+
   4BF−
   4, and possible synthesis of nitrogen pentafluoride". Inorganic Chemistry. 11 (7): 1696–1701. doi:10.1021/ic50113a051.
4. Christe, Karl O; William W. Wilson (December 1992). "Nitrogen pentafluoride: covalent NF5 versus ionic NF4+F− and studies on the instability of the latter". Journal of the American Chemical Society. 114 (25): 9934–9936. doi:10.1021/ja00051a027.
5. Christe, Karl O. (September 1977). "Synthesis and characterization of bis(tetrafluoroammonium) hexafluoronickelate". 16 (9): 2238–2241. doi:10.1021/ic50175a017.
6. Christe, Karl O. (23 May 1980). "Research Studies in NF4+ Salts" (PDF). Rockwell. Retrieved 23 February 2012.
7. Tetrafluoroammonium bifluoride
8. Christe, Karl O.; William W. Wilson; Gary J. Schrobilgen; Raman V. Chirakal; George A. Olah (March 1998). "On the existence of pentacoordinated nitrogen". Inorganic Chemistry. 27 (5): 789–790. doi:10.1021/ic00278a009.
9. Kurzydłowski, Dominik; Zaleski-Ejgierd, Patryk (3 November 2016). "Hexacoordinated nitrogen(V) stabilized by high pressure". Scientific Reports. 6: 36049. doi:10.1038/srep36049. open access
10. Holger F. Bettinger, Paul v. R. Schleyer, and Henry F. Schaefer III (27 October 1998). "NF₅ — Viable or Not?". Journal of the American Chemical Society. 120 (44): 11439–11448. doi:10.1021/ja9813921.