The hexafluoroarsenate (sometimes shortened to fluoroarsenate) anion is a

chemical species A chemical species is a chemical substance or ensemble composed of chemically identical molecular entity, molecular entities that can explore the same set of molecular energy levels on a characteristic or delineated time scale. These energy levels ...

with formula . Hexafluoroarsenate is relatively inert, being the

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

of the notional

superacid In chemistry, a superacid (according to the classical definition) is an acid with an acidity greater than that of 100% pure sulfuric acid (), which has a Hammett acidity function (''H''0) of −12. According to the modern definition, a superacid ...

hexafluoroarsenic acid ().

Synthesis

The first undisputed synthesis is due to

Otto Ruff Otto Ruff (12 December 1871 – 17 September 1939) was a German chemist. Life Otto Ruff was born in Schwäbisch Hall, Württemberg. After becoming a pharmacist under the supervision of Carl Magnus von Hell (known from the Hell-Volhard-Zelinsky ...

, Kurt Stäuber and Hugo Graf, who began with the lower-valent

arsenic trifluoride Arsenic trifluoride is a chemical compound of arsenic and fluorine with the chemical formula AsF3. It is a colorless liquid which reacts readily with water. Preparation and properties It can be prepared by reacting hydrogen fluoride, HF, with ar ...

, using

silver(I) fluoride Silver(I) fluoride is the inorganic compound with the formula AgF. It is one of the three main fluorides of silver, the others being silver subfluoride and silver(II) fluoride. AgF has relatively few niche applications; it has been employed as a ...

as both a fluorine source and

oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

cites but discounts it as describing an implausibly easy synthesis with a hydrolyzable product.

AsF3 + 3AgF + NOCl -> NOAsF6 + AgCl + 2AgIn the following reaction, one mole of arsenic trifluoride, three moles of silver fluoride, and one mole of nitrosyl chloride 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 Arsenic pentafluoride is a chemical compound of arsenic and fluorine. It is a toxic, colorless gas. The oxidation state of arsenic is +5. Synthesis Arsenic pentafluoride can be prepared by direct combination of arsenic and fluorine: :2As + 5F2 � ...

(), which

abstracts An abstract is a brief summary of a research article, thesis, review, academic conference, conference proceedings, proceeding, or any in-depth analysis of a particular subject and is often used to help the reader quickly ascertain the paper's purpo ...

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...

from common donors, such as

hydrogen fluoride Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...

() or ''cis''- difluorodiazine (). Although the hexafluoroarsenate ion is stable against hydrolysis, the related hydroxyfluoroarsenate ion () is not; synthesis of hexafluoroarsenates from

pentavalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of a ...

arsenic

oxides An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

and aqueous

requires thermal

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

or extensive

stoichiometric Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equal ...

excess of the latter. Excerpted in the

Journal of the American Chemical Society The ''Journal of the American Chemical Society'' is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the ''Journal of Analytical ...

, DO
10.1021/ja01564a018

Conjugate acid and other salts

Like its pnictogen congeners, hexafluoroarsenate is a

noncoordinating anion Anions that interact weakly with cations are termed non-coordinating anions, although a more accurate term is weakly coordinating anion. Non-coordinating anions are useful in studying the reactivity of electrophilic cations. They are commonly found ...

, a

counterion 160px, Polystyrene sulfonate, a cation-exchange resin, is typically supplied with as the counterion.">cation-exchange_resin.html" ;"title="Polystyrene sulfonate, a cation-exchange resin">Polystyrene sulfonate, a cation-exchange resin, is typical ...

used to stably store extremely reactive

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s. Through the appropriate choice of fluorine donor, the synthesis of hexafluoroarsenate can also double as preparation of an exotic cation. The resulting salts are typically stable to metathesis with

silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...

(I),

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

, or

cesium Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that ar ...

ions. Unlike the former three, cesium hexafluoroarsenate is

insoluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

in water. Hexafluoroarsenic acid is an extremely

strong acid Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H+, and an anion, A-. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions. ...

and better understood as the

hydron Hydron has the following meanings: * Hydron (chemistry) In chemistry, the hydron, informally called proton, is the cationic form of atomic hydrogen, represented with the symbol . The general term "hydron", endorsed by the IUPAC, encompasses cati ...

salt of hexafluoroarsenate. In solid form, it is

isostructural Isostructural chemical compounds have similar chemical structures. "Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous s ...

with

hexafluorophosphoric acid Hexafluorophosphoric acid is the inorganic compound with the chemical formula (also written ). This strong Brønsted acid features a non-coordinating anion, hexafluorophosphate (). It is formed from the reaction of hydrogen fluoride with phosp ...

and hexafluoroantimonic acid. Also published as NRCC 18823. Nevertheless, the molecule

cocrystal Cocrystals are "solids that are crystalline single phase materials composed of two or more different molecular or ionic compounds generally in a stoichiometric ratio which are neither solvates nor simple salts." A broader definition is that cocryst ...

lizes in solid form with certain hexafluoroarsenate salts, stabilized by a

hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a ...

Applications

Intercalation compound In chemistry, intercalation is the reversible inclusion or insertion of a molecule (or ion) into layered materials with layered structures. Examples are found in graphite and transition metal dichalcogenides. : Examples Graphite One famous int ...

s of

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

and hexafluoroarsenic acid exhibit unusually high conductivity, leading to early proposals that the acid might serve as an

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

in high-energy batteries. Subsequent investigation revealed that the high conductivity occurs because both

electron hole In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle which is the lack of an electron at a position where one could exist in an atom or atomic lattice. Since in a normal atom or ...

s in the graphite and the hexafluoroarsenate ions themselves serve as

charge carrier In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...

References

{{Reflist Superacids Arsenic(V) compounds Fluorine compounds

Synthesis

Conjugate acid and other salts

Applications

See also

References