| 词条 | Tetrafluoroammonium |
| 释义 |
The tetrafluoroammonium cation (also known as perfluoroammonium) is a positively charged polyatomic ion with chemical formula {{chem|NF|4|+}}. It is equivalent to the ammonium ion where the hydrogen atoms surrounding the central nitrogen atom have been replaced by fluorine.[1] Tetrafluoroammonium ion is isoelectronic with tetrafluoromethane {{chem|CF|4}} and the tetrafluoroborate {{chem|BF|4|-}} anion. The tetrafluoroammonium ion forms salts with a large variety of fluorine-bearing anions. These include the bifluoride anion ({{chem|HF|2|-}}), tetrafluorobromate ({{chem|BrF|4|-}}), metal pentafluorides ({{chem|XF|5|-}} where X is Ge, Sn, or Ti), hexafluorides ({{chem|XF|6|-}} where X is P, As, Sb, Bi, or Pt), heptafluorides ({{chem|XF|7|-}} where X is W, U, or Xe), octafluorides ({{chem|XeF|8|2-}}),[2] various oxyfluorides ({{chem|XF|5|O|-}} where X is W or U; {{chem|link=fluorosulfuric acid|FSO|3|-}}, {{chem|BrF|4|O|-}}), and perchlorate ({{chem|ClO|4|-}}).[3] Attempts to make the nitrate salt, {{chem|NF|4|NO|3}}, were unsuccessful because of quick fluorination: {{chem|NF|4|+}} + {{chem|NO|3|-}} → {{chem|NF|3}} + {{chem|FONO|2}}.[4] StructureThe geometry of the tetrafluoroammonium ion is tetrahedral, with an estimated nitrogen-fluorine bond length of 124 pm. All fluorine atoms are in equivalent positions.[5] SynthesisTetrafluoroammonium salts are prepared by oxidising nitrogen trifluoride with fluorine in the presence of a strong Lewis acid which acts as a fluoride ion acceptor. The original synthesis by Tolberg, Rewick, Stringham, and Hill in 1966 employs antimony pentafluoride as the Lewis acid:[5] {{chem|NF|3}} + {{chem|F|2}} + {{chem|SbF|5}} → {{chem|NF|4|SbF|6}} The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride at 120 °C:[5] {{chem|NF|3}} + {{chem|F|2}} + {{chem|AsF|5}} → {{chem|NF|4|AsF|6}} The reaction of nitrogen trifluoride with fluorine and boron trifluoride at 800 °C yields the tetrafluoroborate salt:[5] {{chem|NF|3}} + {{chem|F|2}} + {{chem|BF|3}} → {{chem|NF|4|BF|4}}{{chem|NF|4|+}} salts can also be prepared by fluorination of {{chem|NF|3}} with krypton difluoride ({{chem|KrF|2}}) and fluorides of the form {{chem|MF|n}}, where M is Sb, Nb, Pt, Ti, or B. For example, reaction of {{chem|NF|3}} with {{chem|KrF|2}} and {{chem|TiF|4}} yields {{chem|[NF|4|+|]|2|TiF|6|2-}}.[6] Many tetrafluoroammonium salts can be prepared with metathesis reactions. ReactionsTetrafluoroammonium salts are extremely hygroscopic. The {{chem|NF|4|+}} ion is readily hydrolysed into nitrogen trifluoride, {{chem|H|2|F|+}}, and oxygen gas: 2 {{chem|NF|4|+}} + 2 {{chem|H|2|O}} → 2 {{chem|NF|3}} + 2 {{chem|H|2|F|+}} + {{chem|O|2}} Some hydrogen peroxide ({{chem|H|2|O|2}}) is also formed during this process.[5] Reaction of {{chem|NF|4|+|SbF|6|-}} with alkali metal nitrates yields fluorine nitrate, {{chem|FONO|2}}.[4] PropertiesBecause tetrafluoroammonium salts are destroyed by water, it cannot be used as a solvent. Instead anhydrous hydrogen fluoride or bromine pentafluoride can be used as a solvent to dissolve these salts.[7] Tetrafluoroammonium salts usually have no colour. However some are coloured due to other metals in them. Red salts include {{chem|(|NF|4|+|)|2|CrF|6|2-}}, {{chem|(|NF|4|+|)|2|NiF|6|2-}} and {{chem|(|NF|4|+|)|2|PtF|6|2-}}. {{chem|(|NF|4|+|)|2|MnF|6|2-}}, {{chem|NF|4|+|UF|7|-}}, {{chem|NF|4|+|UOF|5|-}} and {{chem|NF|4|+|XeF|7|-}} are yellow.[7] Applications{{chem|NF|4|+}} salts are important for solid propellant {{chem|NF|3|–F|2}} gas generators. They are also used as reagents for electrophilic fluorination of aromatic compounds in organic chemistry.[8]See also
References1. ^{{Cite journal| first1 = I. V.| first2 = V. Y.| title = Tetrafluoroammonium Salts| last1 = Nikitin| journal = Russian Chemical Reviews| volume = 54| issue = 5| pages = 426| year = 1985| doi = 10.1070/RC1985v054n05ABEH003068| last2 = Rosolovskii|bibcode = 1985RuCRv..54..426N }} 2. ^{{Cite journal | journal = Inorganic Chemistry | title = Perfluoroammonium and alkali-metal salts of the heptafluoroxenon(VI) and octafluoroxenon(VI) anions| last1 = Christe| issue = 12| first2 = W. W. | volume = 21 | year = 1982 | doi = 10.1021/ic00142a001| last2 = Wilson| first1 = K. O. | pages = 4113–4117}} 3. ^{{Cite journal| first1 = K. O.| first2 = W. W.| title = Synthesis and characterization of tetrafluoroammonium(1+) tetrafluorobromate(1-) and tetrafluoroammonium(1+) tetrafluorooxobromate(1-)| journal = Inorganic Chemistry| volume = 25| issue = 11| pages = 1904–1906| year = 1986| last1 = Christe| doi = 10.1021/ic00231a038| last2 = Wilson}} 4. ^1 {{Cite journal| first1 = B.| last2 = Christe | first2 = K. O.| title = On the stability of NF{{su|b=4|p=+}}NO{{su|b=3|p=−}} and a new synthesis of fluorine nitrate| journal = Journal of Fluorine Chemistry| last1 = Hoge| volume = 110| issue = 2| pages = 87–88| year = 2001| doi = 10.1016/S0022-1139(01)00415-8}} 5. ^{{cite book|first1 = Pradyot|last1 = Patnaik|title = Handbook of inorganic chemicals|publisher = McGraw-Hill Professional|year = 2002|isbn = 0-07-049439-8}} 6. ^{{cite book| title = Advances in Inorganic Chemistry| author = John H. Holloway| author2 = Eric G. Hope| editor = A. G. Sykes| publisher = Academic Press| year = 1998| isbn = 0-12-023646-X| pages = 60–61}} 7. ^1 {{cite book|last=Sykes|first=A. G.|title=Advances in Inorganic Chemistry|url=https://books.google.com/books?id=qzN5pnPwuaoC&pg=PA154|accessdate=22 June 2014|date=1989-07-17|publisher=Academic Press|isbn=9780080578828|page=154}} 8. ^1 2 3 4 {{cite book| last1 = Sykes| first1 = A. G.| title = Advances in Inorganic Chemistry| publisher = Academic Press| year = 1989| isbn = 0-12-023633-8}} 3 : Cations|Nitrogen fluorides|Fluorinating agents |
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