The Existence of Hexafluoroarsenic(V) Acid

Abstract

The homogeneous mixture of anhydrous hydrogen fluoride aHF and antimony pentafluoride AsF5 is known as a superacidic system. The high acidity is derived from the formation of [H2F](+) [AsF6](-). No experimental evidence exists for the existence of the free acid molecule HAsF6. The reaction of trimethylsilyl N,N-dimethylcarbamate in the binary system aHF/AsF5 led to decomposition of trimethylsilyl N,N-dimethylcarbamate at -50 °C to dimethylammonium hexafluoridoarsenate and cocrystallization of HAsF6. The single-crystal X-ray structure displays an HAsF6 molecule involved in an asymmetric hydrogen bridge to the hexafluoridoarsenate anion. As a result of the incalculable situation in the crystal lattice, the molecular structure of HAsF6 is calculated by quantum chemical structure optimization of the extreme cases of [FHF-AsF5](-) (strong hydrogen bond) and HAsF6 (no hydrogen bond) at the PBE1PBE/6-311G(3df,3pd) level of theory.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[11,260] Recently, however, the presence of H[AsF 6 ]h as been identified in the solid state.T he reaction between the superacidic system of anhydrous HF with AsF 5 and trimethylsilyl N,N-dimethylcarbamate proceeds at À50 8 8Cb ye limination of Me 3 SiF and formation of N,N-dimethylcarbamic acid, which subsequently decomposes through carbon dioxide elimination to yield the N,N-dimethylammonium cation. [261] In as imilar manner, the presence of H[SbF 6 ]w as identified in the solid state by crystallization of an arrested state of the salt metathesis reaction between IPr-InBr 3 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene) and Ag [SbF 6 ]. [261] In as imilar manner, the presence of H[SbF 6 ]w as identified in the solid state by crystallization of an arrested state of the salt metathesis reaction between IPr-InBr 3 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene) and Ag [SbF 6 ].…”

“…Crystallization under appropriate conditions yields crystals of [(Me) 2 NH 2 ][AsF 6 ]·HAsF 6 , in which the HAsF 6 molecule is involved in an asymmetric hydrogen bridge to the [AsF 6 ] À ion. [261] In as imilar manner, the presence of H[SbF 6 ]w as identified in the solid state by crystallization of an arrested state of the salt metathesis reaction between IPr-InBr 3 (IPr = 1,3-bis (2,6- [262] At the Acidity Limit:C arborane-Based Neutral Acids: Thes trongest known Brønsted acids belong to the H[WCA] family,w here WCA is ac arborane anion, and are typically synthesized through the reaction of the silylated carborane anion with HCl [see Eq. (10) above].…”

First Evidence for the Existence of Hexafluoroantimonic(V) Acid

“…As am atter of comparison, the corresponding AsÀFb ond length in HAsF 6 is also very long (1.979(2) ). [1] Similarly to HAsF 6 ,t he four fluorine atoms in the equatorial plane of HSbF 6 are puckered towards the HF moiety.…”

“…To explain its formation,w es uppose that as pecies of type [IPr·InBr 3Àx ][SbF 6 ] x (x = 1, 2, or 3), formed after anion metathesis [Eq. (1)],r eacted with the water residue contained in the solvent, or in the hygroscopic silver salt, to give the corresponding indium hydroxide and HSbF 6 (1), [12] in which Ag + is coordinated to Br [Eq. (3)].…”

Icosahedral Carborane Superacids and their Conjugate Bases Comprising H, F, Cl, and CN Substituents: A Theoretical Investigation of Monomeric and Dimeric Cages

“…[1] However, more systematic studies that eventually led to development of 'superacid chemistry' were performed much later (in the 60s and 70s) by Olah and Hogeveen who studied non-aqueous systems (such as SbF 5 /HF and HSO 3 F/SbF 5 ) [2][3][4][5][6][7] and by Gillespie who formulated the first definition of a 'superacid' as any acid stronger than 100 % sulfuric acid (i. e., having its Hammett acidity function H 0 smaller than À 12). [8,9] Due to their unusual properties, superacids are the subject of ongoing theoretical [10][11][12][13][14] and experimental [15][16][17][18][19][20][21][22][23][24] investigations focused mainly on their structure, acidity, and stability. Our contribution to these studies include predicting the acidity of the aluminumbased Al n F 3n /HF (n = 1-4) systems [25] and the compounds containing In, Sn and Sb, [26] Au, [27] Ti and Ge, [28] investigating the saturation of the acidity of nHF/AlF 3 and nHF/GeF 4 (n = 1-6) superacids caused by increasing the number of surrounding HF molecules, [29] describing the fragmentation process of the HAlF 4 and HGaF 4 superacids induced by an excess electron attachment, [30,31] and demonstrating the catalytic usefulness of various superacids.…”