| 词条 | Perxenate |
| 释义 |
In chemistry, perxenates are salts of the yellow[1] xenon-containing anion {{chem|XeO|6|4-}}.[1] This anion has octahedral molecular geometry, as determined by Raman spectroscopy, having O–Xe–O bond angles varying between 87° and 93°.[2] The Xe–O bond length was determined by X-ray crystallography to be 1.875 Å.[3] SynthesisPerxenates are synthesized by the disproportionation of xenon trioxide when dissolved in strong alkali:[4] 2 XeO3 (s) + 4 OH− (aq) → Xe (g) + {{chem|XeO|6|4-}} (aq) + O2 (g) + 2 H2O (l) When Ba(OH)2 is used as the alkali, barium perxenate can be crystallized from the resulting solution.[4] Perxenic acidPerxenic acid is the unstable conjugate acid of the perxenate anion, formed by the solution of xenon tetroxide in water. It has not been isolated as a free acid, because under acidic conditions it rapidly decomposes into xenon trioxide and oxygen gas:[5][6] 2 {{chem|HXeO|6|3-}} + 6 {{chem|H|+}} → 2 {{chem|XeO|3}} + 4 {{chem|H|2|O}} + {{chem|O|2}} Its extrapolated formula, H4XeO6, is inferred from the octahedral geometry of the perxenate ion ({{chem|XeO|6|4-}}) in its alkali metal salts.[5][3] The pKa of aqueous perxenic acid has been indirectly calculated to be below 0, making it a very strong acid. Its first ionization yields the anion {{chem|H|3|XeO|6|-}}, which has a pKa value of 4.29, still relatively acidic. The twice deprotonated species {{chem|H|2|XeO|6|2-}} has a pK value of 10.81.[7] Due to its rapid decomposition under acidic conditions as described above, however, it is most commonly encountered as perxenate salts, bearing the anion {{chem|XeO|6|4-}}.[5][1] PropertiesPerxenic acid and the anion {{chem|XeO|6|4-}} are both strong oxidizing agents,[8] capable of oxidising silver(I) to silver(III), copper(II) to copper(III),[15] and Mn2+ to {{chem|MnO|4|-}}.[9] The perxenate anion is unstable in acidic solutions,[15] being almost instantaneously reduced to {{chem|HXeO|4|-}}.[10] The sodium, potassium, and barium salts are soluble.[11] Barium perxenate solution is used as the starting material for the synthesis of xenon tetroxide (XeO4) by mixing it with concentrated sulfuric acid:[12] Ba2XeO6 (s) + 2 H2SO4 (l) → XeO4 (g) + 2 BaSO4 (s) + 2 H2O (l) Most metal perxenates are stable, except silver perxenate, which decomposes violently.[13] ApplicationsSodium perxenate, Na4XeO6, can be used for the analytic separation of trace amounts of americium from curium. The separation involves the oxidation of Am3+ to Am4+ by sodium perxenate in acidic solution in the presence of La3+, followed by treatment with calcium fluoride, which forms insoluble fluorides with Cm3+ and La3+, but retains Am4+ and Pu4+ in solution as soluble fluorides.[8] References1. ^1 {{Holleman&Wiberg|page=399}} {{Xenon compounds}}{{Noble gas compounds}}{{inorganic-compound-stub}}2. ^{{Cite journal| last1 = Peterson | first1 = J. L.| last2 = Claassen | first2 = H. H.| last3 = Appelman | first3 = E. H.| title = Vibrational spectra and structures of xenate(VI) and perxenate(VIII) ions in aqueous solution| journal = Inorganic Chemistry | volume = 9| issue = 3| pages = 619–621 | date=March 1970 | doi = 10.1021/ic50085a037}} 3. ^1 {{Cite journal | author1 = Hamilton| last3 = MacKenzie| last2 = Ibers | first2 = J. | first3 = D. | title = Geometry of the Perxenate Ion | journal = Science | volume = 141 | issue = 3580 | pages = 532–534 | date=Aug 1963 | issn = 0036-8075 | pmid = 17738629 | doi = 10.1126/science.141.3580.532|bibcode = 1963Sci...141..532H }} 4. ^1 {{cite book| title = Elements of the p block (volume 9 of Molecular world)| author1 = Charlie Harding| author2 = David Arthur Johnson| author3 = Rob Janes| publisher = Royal Society of Chemistry| year = 2002| isbn = 0-85404-690-9| page = 93}} 5. ^1 2 {{Cite journal | last1 = Klaening | first1 = U. K.|last2 = Appelman | first2 =E. H.| title = Protolytic properties of perxenic acid| journal = Inorganic Chemistry | volume = 27 | issue = 21| pages = 3760–3762 | date=October 1988 | doi = 10.1021/ic00294a018}} 6. ^{{Holleman&Wiberg|page=400}} 7. ^{{cite book| title = Advances in Inorganic Chemistry| volume = 46| author1 = John H. Holloway| author2 = Eric G. Hope| editor = A. G. Sykes| publisher = Academic Press| year = 1998| isbn = 0-12-023646-X| page = 67}} 8. ^1 {{Cite journal| first1 = H. P. | title = Analytical Oxidation of Americium with Sodium Perxenate | journal = Analytical Chemistry | volume = 37| issue = 3 | page = 415| last1 = Holcomb | date=March 1965 | doi = 10.1021/ac60222a002}} 9. ^{{cite book| title = General chemistry| author = Linus Pauling| edition = 3rd| publisher = Courier Dover Publications| year = 1988| isbn = 0-486-65622-5| page = 251}} 10. ^1 {{Cotton&Wilkinson6th|page=593}} 11. ^{{cite book| title = Concise encyclopedia chemistry| author = Thomas Scott| author2 = Mary Eagleson| publisher = Walter de Gruyter| year = 1994| isbn = 3-11-011451-8| page = 1183}} 12. ^{{cite book| title = Elements of the p block| author = Charlie Harding| author2 = David Arthur Johnson| author3 = Rob Janes| location = Great Britain| publisher = Royal Society of Chemistry| year = 2002| isbn = 0-85404-690-9| pages = 92–93}} 13. ^1 2 {{cite book| title = Standard Potentials in Aqueous Solution| author = Allen J. Bard| author2 = Roger Parsons| author3 = Joseph Jordan| author4 = International Union of Pure and Applied Chemistry| publisher = CRC Press| year = 1985| isbn = 0-8247-7291-1| page = 778}} 3 : Anions|Salts|Xenon compounds |
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