Nitrogen pentafluoride

A variety of other tetrafluoroammonium salts are known ({{chem2|[NF4]+X−}}), as are fluoride salts of other ammonium cations ({{chem2|[NR4]+F−}}).

In 1966, W. E. Tolberg first synthesized a five-valent nitrogen compound of nitrogen and fluorine when tetrafluoroammonium compounds, tetrafluoroammonium hexafluoroantimonate(V) {{chem2|[NF4]+[SbF6]−}} and tetrafluoroammonium hexafluoroarsenate(V) {{chem2|[NF4]+[AsF6]−}} were made.{{cite journal |last=Goetschel |first=C. T. |author2=V. A. Campanile |author3=R. M. Curtis |author4=K. R. Loos |author5=C. D. Wagner |author6=J. N. Wilson |display-authors=3|title=Preparation and properties of perfluoroammonium tetrafluoroborate, [NF₄]⁺[BF₄]⁻, and possible synthesis of nitrogen pentafluoride |date=July 1972 |journal=Inorganic Chemistry |volume=11 |issue=7 |pages=1696–1701 |doi=10.1021/ic50113a051}} In 1971 C. T. Goetschel announced the preparation of {{chem2|[NF4]+[BF4]−}} and also produced a white solid assumed to be tetrafluoroammonium fluoride ({{chem2|[NF4]+F−}}). This was made by treating nitrogen trifluoride and fluorine with 3 MeV electron radiation at 77 K. It decomposed above 143 K back into those ingredients. Theoretical studies also show the ionic compound is very likely to decompose to nitrogen trifluoride and fluorine gas.{{cite journal |last=Christe |first=Karl O. |author2=William W. Wilson |date=December 1992 |title=Nitrogen pentafluoride: covalent NF₅ versus ionic NF₄⁺F⁻ and studies on the instability of the latter |journal=Journal of the American Chemical Society |volume=114 |issue=25 |pages=9934–9936 |doi=10.1021/ja00051a027|bibcode=1992JAChS.114.9934C }}

Karl O. Christe synthesised bis(tetrafluoroammonium) hexafluoronickelate(IV) {{chem2|([NF4]+)2[NiF6](2−)}}.{{cite journal |last=Christe |first=Karl O. |date=September 1977 |title=Synthesis and characterization of bis(tetrafluoroammonium) hexafluoronickelate |journal=Inorganic Chemistry |volume=16 |issue=9 |pages=2238–2241 |doi=10.1021/ic50175a017}} He also prepared compounds with manganese, a fluorouranate, tetrafluoroammonium perchlorate {{chem2|[NF4]+ClO4−}}, tetrafluoroammonium fluorosulfate {{chem2|[NF4]+SO3F−}} and {{chem2|[N2F3]+}} (trifluorodiazenium) salts.{{cite web |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a086981.pdf |archive-url=https://web.archive.org/web/20151227005623/http://www.dtic.mil/dtic/tr/fulltext/u2/a086981.pdf |url-status=live |archive-date=December 27, 2015 |title=Research Studies in NF₄⁺ Salts |last=Christe |first=Karl O. |date=23 May 1980 |publisher=Rockwell |accessdate=23 February 2012}} Christe attempted to make {{chem2|[NF4]+F−}} by metathesis of {{chem2|[NF4]+[SbF6]−}} with CsF in HF solvent at 20 °C. However, a variant, tetrafluoroammonium bifluoride hydrofluorates ({{chem2|[NF4]+[HF2]−*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 Fluorine, HF and Nitrogen trifluoride as gases. This has CAS number 71485-49-9.Tetrafluoroammonium bifluoride

I. J. Solomon believed that nitrogen pentafluoride was produced by the thermal decomposition of {{chem2|[NF4]+[AsF6]−}}, but experimental results were not reproduced.{{cite journal |last=Christe |first=Karl O.|author2=William W. Wilson |author3=Gary J. Schrobilgen |author4=Raman V. Chirakal |author5=George A. Olah |display-authors=3|date=March 1998 |title=On the existence of pentacoordinated nitrogen |journal=Inorganic Chemistry |volume=27 |issue=5 |pages=789–790 |doi=10.1021/ic00278a009}}

Dominik Kurzydłowski and Patryk Zaleski-Ejgierd predict that a mixture of fluorine and nitrogen trifluoride under pressure between 10 and 33 GPa forms {{chem2|[NF4]+F−}} with space group R3m. This is a high-pressure oxidation. Over 33 GPa it will form a stable ionic compound with formula {{chem2|([NF4]+)2[NF6]−F–}} (bis(tetrafluoroammonium) hexafluoronitrate(V) fluoride) with space group I4/m. Over 151 GPa this is predicted to transform to {{chem2|[NF4]+[NF6]−}} (tetrafluoroammonium hexafluoronitrate(V)) with space group P4/n.{{cite journal |last1=Kurzydłowski |first1=Dominik |last2=Zaleski-Ejgierd |first2=Patryk |title=Hexacoordinated nitrogen(V) stabilized by high pressure |journal=Scientific Reports |date=3 November 2016 |volume=6 |pages=36049 |doi=10.1038/srep36049 |pmid=27808104 |pmc=5093683 |bibcode=2016NatSR...636049K}} {{open access}} A {{chem2|NF5}} molecular compound is not stable under any pressure conditions.

NF4F.jpg|{{chem2|[NF4]+F−}} R3m structure

NF4-2NF6F.jpg|{{chem2|([NF4]+)2[NF6]−F−}} I4/m structure

NF4NF6.jpg|{{chem2|[NF4]+[NF6]−}} P4/n structure

File:Nitrogen pentafluoride possible structures.jpg

For a {{chem2|NF5}} molecule to form, five fluorine atoms have to be arranged around a nitrogen atom. There is insufficient space to do this at typical nitrogen–fluorine covalent-bond lengths, so at least some bonds are forced to be longer. Calculations show that fragmentation to form {{chem2|NF4}} and F radicals would have a transition state barrier of around {{convert|15.8-20.0|kcal/mol|kJ/mol|order=flip|abbr=on}} and that this process is thermodynamically favourable (exothermic) by {{convert|9|kcal/mol|kJ/mol|order=flip|abbr=on}}.{{cite journal|author1=Holger F. Bettinger |author2=Paul v. R. Schleyer |author3=Henry F. Schaefer III |title=NF₅ — Viable or Not?|journal=Journal of the American Chemical Society|date=27 October 1998|volume=120|issue=44|pages=11439–11448|doi=10.1021/ja9813921|bibcode=1998JAChS.12011439B }} Nitrogen pentafluoride also violates the octet rule in which compounds with eight outer shell electrons are particularly stable.{{cite book|last=Lewars|first=Errol G. |title=Modeling marvels: computational anticipation of novel molecules|chapter-url=https://books.google.com/books?id=IoFzgBSSCwEC|date=3 November 2008|publisher=Springer|pages=53–67|chapter=Nitrogen Pentafluoride and Related Compounds|isbn=978-1-4020-6972-7|doi=10.1007/978-1-4020-6973-4_4}}{{clear}}

{{reflist|30em}}

{{Nitrogen compounds}}

{{Fluorides}}

Category:Nitrogen fluorides

Category:Hypothetical chemical compounds

Category:Nitrogen(V) compounds