Английская Википедия:Hexafluoroarsenate
The hexafluoroarsenate (sometimes shortened to fluoroarsenate) anion is a chemical species with formula Шаблон:Chem2. Hexafluoroarsenate is relatively inert, being the conjugate base of the notional superacid hexafluoroarsenic acid (Шаблон:Chem2).
Synthesis
The first undisputed synthesis is due to Otto Ruff, Kurt Stäuber and Hugo Graf, who began with the lower-valent arsenic trifluoride, using silver(I) fluoride as both a fluorine source and oxidant:[1] <chem display=block>AsF3 + 3AgF + NOCl -> NOAsF6 + AgCl + 2Ag</chem>In the following reaction, one mole of arsenic trifluoride, three moles of silver fluoride, and one mole of nitrosyl chloride are reacted to produce one mole of nitrosyl hexafluoroarsenate, one mole of silver chloride, and two moles of elemental silver.
Modern syntheses usually begin with arsenic pentafluoride (Шаблон:Chem2), which abstracts fluoride from common donors, such as hydrogen fluoride (Шаблон:Chem2) or cis-difluorodiazine (Шаблон:Chem2).[2] Although the hexafluoroarsenate ion is stable against hydrolysis, the related hydroxyfluoroarsenate ion (Шаблон:Chem2) is not; synthesis of hexafluoroarsenates from pentavalent arsenic oxides and aqueous hydrogen fluoride requires thermal dehydration or extensive stoichiometric excess of the latter.[3][4]
Conjugate acid and other salts
Like its pnictogen congeners, hexafluoroarsenate is a noncoordinating anion, a counterion used to stably store extremely reactive cations.[5] Through the appropriate choice of fluorine donor, the synthesis of hexafluoroarsenate can also double as preparation of an exotic cation.[2][6] The resulting salts are typically stable to metathesis with silver(I), ammonium, potassium, or caesium ions.[3][2] Unlike the former three, caesium hexafluoroarsenate is insoluble in water.
Hexafluoroarsenic acid is an extremely strong acid. The anhydrous compound has been analyzed by X-ray crystallography, which reveals hexafluoroarsenate with a proton attached to one fluoride.[7] The more commonly encountered hydrate is isostructural with the hydrates off hexafluorophosphoric acid and hexafluoroantimonic acid.[8] These salts contain MF6− (M = P, As, Sb), HF, and water.
Applications
Intercalation compounds of graphite and hexafluoroarsenic acid exhibit unusually high conductivity, leading to early proposals that the acid might serve as an electrode or electrolyte in high-energy batteries.[9][4] Subsequent investigation revealed that the high conductivity occurs because both electron holes in the graphite and the hexafluoroarsenate ions themselves serve as charge carriers.[9][10]
See also
- Шаблон:Annotated link
- Hexafluorophosphate — phosphorus analogue
- Шаблон:Annotated link
- Шаблон:Annotated link
References
- ↑ Шаблон:Cite journal
Шаблон:Harvnb cites Шаблон:Cite journal but discounts it as describing an implausibly easy synthesis with a hydrolyzable product.
- ↑ 2,0 2,1 2,2 Шаблон:Cite journal
- ↑ 3,0 3,1 Шаблон:Cite thesis Excerpted in the Journal of the American Chemical Society, DOI 10.1021/ja01564a018.
- ↑ 4,0 4,1 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal Also published as NRCC 18823.
- ↑ 9,0 9,1 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
