Does the protonation of superhalogen anions always lead to superacids?

The saturation of the gas phase acidity of nHF/AlF3 and nHF/GeF4 (n = 1–6) superacids caused by increasing the number of surrounding HF molecules

“…The simplest case of the AlF 3 Lewis acid interacting with one HF molecule, HF/AlF 3 (HAlF 4 ), has already been characterized as a superacid composed of the hydrogen uoride donating its uorine's lone pair to the empty Al's 3p atomic orbital of AlF 3 quasi-planar fragment and additionally stabilized by the FH/F 3 Al hydrogen bond. 21,22,28 The DE of 279-280 kcal mol À1 and DG acid of 267-269 kcal mol À1 (depending on the theory level employed) 21,22,28 were predicted for this superacid, however, in this contribution we assume the DE ¼ 279 kcal mol À1 and DG acid ¼ 267 kcal mol À1 values for consistency with the results presented for the remaining nHF/ AlF 3 (n ¼ 2-6) systems. The 2HF/AlF 3 species might be viewed as formed by the attachment of the second HF molecule to the HF/ AlF 3 system, hence it resembles the deformed neutral AlF 3 molecule with two HF moieties attached, see structure 2HF/AlF 3 (1) in Fig.…”

“…1,2 Since then, superacids remain the subject of continuing theoretical [10][11][12][13] and experimental [14][15][16][17][18][19] investigations concerning their structure, stability and acidity. Our group contributed to these studies by addressing the issue of the HAlCl 4 instability, 20 predicting the acidic strength of the aluminum-based HF/AlF 3 (HAlF 4 ), HF/Al 2 F 6 (HAl 2 F 7 ), HF/Al 3 F 9 (HAl 3 F 10 ), and HF/Al 4 F 12 (HAl 4 F 13 ) systems, 21 investigating the dissociative excess electron attachment to the HAlF 4 superacid 22 (whose properties were earlier determined by the Radom group 23,24 ), examining the strength of the Brønsted/Lewis superacids containing In, Sn, and Sb (i.e., HIn n F 3n+1 , HSn n F 4n+1 , and HSb n F 5n+1 (n ¼ 1-3)), 25 and, most recently, by demonstrating that the protonation of superhalogen anions 26,27 might be considered as the route to superacids' formation in selected cases only, 28 despite the fact that various superhalogens containing heavy metals as central atoms (e.g., InF 4 , SbF 6 , Sb 2 F 11 , SnF 5 , Sn 2 F 9 ) were utilized in the past to create atypical salts and complexes [29][30][31][32][33][34][35] even with noble gases (Kr and Xe). [36][37][38][39] The Lewis-Brønsted superacids consist of strong Lewis acid molecules (such as AlF 3 ) interacting with strong Brønsted acid molecules (e.g., HF) and thus their deprotonation process might be described by the following reaction scheme (that assumes the excess of a representative Brønsted acid): nHF/AlF 3 / ((n À 1)HF/AlF 4 ) À + H + .…”

The Acid Strength of the Lewis‐Brønsted Superacids – A QSPR Study

“…[8] It has been also established that the protonation of superhalogen anions [9] might be utilized as a convenient path to superacids' formation in selected cases. [10] The versatility of successful applications of such aluminum based superacids has been demonstrated by various experimental groups, e. g., HBr/AlBr 3 was used either as the catalyst (in benzophenone hydrogenation, [11] in the direct conversion of methane to higher hydrocarbons [12] ) or in protonation of benzene. [13] Most recently, it was demonstrated that one of the most important reaction involving the syngas, namely, the carbon monoxide hydrogenation yielding formaldehyde, might be effectively catalyzed with the use of either HAlF 4 or HSbF 6 superacid.…”

Toward the preparation of the HAuF6, HAu2F11, and HAu3F16 superacids: Theoretical study

“…Due to their unusual properties, superacids are still the subjects of both theoretical and experimental investigations . Recently, we proposed a novel scheme which allows to obtain superacid systems utilizing the superhalogen anions as their precursors by demonstrating that a Lewis‐Brønsted superacid might be viewed as a compound formed by attaching the additional proton to the properly chosen superhalogen anion. Conversely, superhalogen anions are the compounds characterized by the extremely large values (approaching 14 eV in certain cases) of the vertical electron detachment energy (VDE) .…”