Hexafluoroarsenate ion

Arsenic forms the binary compounds arsenous triduoride and arsenic pentafluoride, as well as a series of compounds and the acid of the very stable hexafluoroarsenate ion. 

Because of the special stabiHty of the hexafluoroarsenate ion, there are a number of appHcations of hexafluoroarsenates. For example, onium hexafluoroarsenates (33) have been described as photoinitiators in the hardening of epoxy resins (qv). Lithium hexafluoroarsenate [29935-35-1] has been used as an electrolyte in lithium batteries (qv). Hexafluoroarsenates, especially alkaH and alkaline-earth metal salts or substituted ammonium salts, have been reported (34) to be effective as herbicides (qv). Potassium hexafluoroarsenate [17029-22-0] has been reported (35) to be particularly effective against prickly pear. However, environmental and regulatory concerns have severely limited these appHcations. 

Durham polyacetylene has the advantage of being a uniform, dense film and so lends itself much more readiliy to diffusion studies. In addition, the uniform morphology is much better suited to device applications, although the low surface area would limit applications in batteries. We have made extensive measurements on the doping of Durham frans-polyacetylene by gaseous AsF5 514 515), which is believed to dope the polymer to form the hexafluoroarsenate ion and arsenic trifluoride 516 ... 

Arsenic trifluoride (arsenic(III) fluoride), AsF, can be prepared by reaction of arsenic trioxide with a mixture of sulfuric acid and calcium fluoride or even better with fluorosulfonic acid. Chlorine reacts with ice-cold arsenic trifluoride to produce a hygroscopic soHd compound, arsenic dichloride trifluoride [14933-43-8] ASCI2F35 consisting of AsQ. and AsF ions (21). Arsenic trifluoride forms a stable adduct, 2AsF2 SSO, with sulfur trioxide and reacts with nitrosyl fluoride to give nitrosonium hexafluoroarsenate(V) [18535-07-4] [NO][AsFg]. 

Olah et al.603 have observed the formation of cation 309 (protonated fluorometha-nol) upon treatment of formaldehyde in HF-SbF5 [Eq. (3.81)]. When Minkwitz et al.605 attempted to isolate salts of the ion, however, the hydroxymethyl(methylidene) oxonium ion 310 was obtained [Eq. (3.81)]. Crystal structure analysis of the hexafluoroarsenate salt shows that cations and anions are connected by short H -F distances, forming a three-dimensional network. The bond lengths of the C-0=C fragment (1.226 and 1.470 A) are longer than those in formaldehyde (1.208 A) and dimethyl ether (1.410 A). The C—O—C bond angle is 121.2°. 

Heptafluoro-l,4-cyclohexadien-l-yl) xenon(ll) hexafluoroarsenate and (non-afluorocyclohexen-l-yl) xenon(ll) hexafluoroarsenate reacted with bromide ion in acetonitrile and formation of l-bromoheptafluoro-l,4-cyclohexadiene or 1-bromo-nonafluorocyclohexene, respectively, was established13. Similar reaction with benzene gave l-phenylheptafluoro-l,4-cyclohexadiene or 1-phenylnonafluorocyclohexene (Scheme 36). 

Little is known about the chemical reactions of these salts. The hexafluoroarsenate decomposes without melting at 150°C, but N2F+BF4 is 75% decomposed in 1 hr at ambient temperature. The N2F+ and N02+ ions are isoelectronic and the X-ray patterns of N2FAsF6 and N02AsF6 are very similar. Few reactions have been reported. The hexafluoroarsenate is decomposed by water to N20, HF, and HAsF6. With 02 at 2 atm, the reaction products are 02AsF6, N2, and cis-N2F2. The cis isomer is also formed in the reaction with either NO or (NaF + HF). 

Lithium tetrafluoroborate, (LiBF4), lithium hexafluorophosphate, (LiPF6), lithium hexafluoroarsenate, (LiAsF ), lithium trifluoromethane sulfonate, (LiSOjCFj), are the electrolyte salts of the 21st Century. The performance of lithium ion cells, primary and secondary lithium cells depends on the purity of these compounds. Several hundred tons of these materials have been produced and many more tons — and perhaps thousands of tons — will be required in the near future. One of the largest automotive producers predicts that there may be a market for 10-15 million pounds of these salts. The demand for Lithium ion primary cells is also very huge in electronics, computers, communication systems and military applications. 

Because of their strong inductive destabilization, few salts of a- or /i-fluorocarbe-nium ions have been isolated and characterized. Despite persistent attempts to isolate salts of the CF3+ cation, this most simple a-fluorocarbenium ion has so far only been subject of numerous theoretical studies [3]. Recently, the more stable dimethylfluorocarbenium ion, in the form of its hexafluoroarsenate salt (MeyCf Asf, ), has been characterized by X-ray crystallography [4]. 

Fluorodiazonium hexafluoroarsenate ( — = N AsFg" a white solid) was first prepared by Moy and Young (1965) by fluoride ion abstraction from (Z)-difluorodiazene by ASF5 at low temperature (3-14) (see also Bormann and Glemser, 1966 Pankratov and Savenkova, 1968). Christe et al. (1991) prepared the corresponding hexafluoroantimonate salt FN SbFg . 

The synthesis of the pentanitrogen cation (6) marks a milestone in polynitrogen chemistry [32], because this is only the second poly nitrogen to have been actually isolated, as (hstinct from just spectroscopically detected. Salts of the azide ion were first reported in 1890 [27], and salts of the pentanitrogen cation in 1999 [18], The hiatus suggests that the synthesis of polynitrogens involves problems. The first Ns salt used the hexafluoroarsenate counterion ... 

The first crystallographic confirmation of the Hgs + ion has been reported, in the form of its hexafluoroarsenate salt. The cation is centro-symmetric and, therefore, strictly linear, with a unique Hg-Hg distance of 2.55 A. 

The electrolyte solution consists of a lithium salt in an organic solvent. Commonly used salts include lithium hexafluorophosphate, lithium perchlorate, lithium tetra-fluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, and lithium tetraphen)dborate. Organic solvents used in the electrolyte solution are ethylene carbonate, dieth)d carbonate, dimethyl carbonate, methyl ethyl carbonate, and propylene carbonate, to name the most important ones. When a lithium ion battery is charged, the positive lithium ions move from the positive electrode to the negative one. The process to insert the lithium ions into the graphite electrode is called intercalation. When the cell is discharging, the reverse occurs. 

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