HAlCl4 in the gas phase is stronger than HTaF6

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

“…Therefore, we conclude that although the 1-H(CHB 11 Cl 11 ) structure corresponds to the most stable isomer, the acidic proton exhibits relatively large mobility which renders the temporary existence of the isomer 2-H(CHB 11 Cl 11 ) plausible. Moreover, our results indicate that the proton is expected to 'travel' among the substituent Cl 1 and its neighboring five chlorine substituents (Cl 2 À Cl 6 ) connected to the 'upper' five-member boron ring whereas its migration to the substituents C 7 À Cl 11 connected to the 'lower' boron ring (which would result in the formation of the 4-H(CHB 11 Cl 11 ) isomer) should not be expected. We believe that these conclusions might be also valid for the H(CHB 11 X 11 ) superacids containing different halogen substituents (e. g., fluorine atoms).…”

“…Clearly, the presence of that additional proton breaks the C 5v -symmetry (typical for the corresponding anions, see the preceding section). As shown in Figure 2, the structures with either F or Cl substituents are additionally stabilized by the X 1 -H···X 2 (X 1 , X 2 = F, Cl) hydrogen bonds formed between the neighboring halogen atoms whereas analogous H-bonds are absent in both H(CHB 11 H 11 ) and H(CHB 11 (CN) 11 ).…”

“…Moreover, according to our calculations, the conversion between 1-H(CHB 11 Cl 11 ) and 2-H(CHB 11 Cl 11 ) via the proton transfer from Cl 1 to Cl 2 as well as the conversion between two equivalent structures 2-H(CHB 11 Cl 11 ) via the proton transfer from Cl 2 to Cl 3 (and vice versa) seem plausible as the heights of the corresponding kinetic barriers for these processes do not exceed 3 kcal/mol. On the other hand, the conversion of 2-H(CHB 11 Cl 11 ) into 3-H(CHB 11 Cl 11 ) and the 3-H (CHB 11 Cl 11 )!4-H(CHB 11 Cl 11 ) isomerization would require surmounting larger kinetic barriers (exceeding 5 kcal/mol) and should be considered less likely as such. Therefore, we conclude that although the 1-H(CHB 11 Cl 11 ) structure corresponds to the most stable isomer, the acidic proton exhibits relatively large mobility which renders the temporary existence of the isomer 2-H(CHB 11 Cl 11 ) plausible.…”

“…[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.…”

The HAlF4 superacid fragmentation induced by an excess electron attachment

“…In fact, the term superacid appeared in the scientific literature much earlier, namely, in the article written by Hall and Conant in 1927 who provided a description of the salts produced by perchloric acid and sulfuric acid in glacial acetic acid reacting with weak bases. 14,15 Recently, 16 we proposed a few more compounds (i.e., HAl 2 F 7 , HAl 3 F 10 , and HAl 4 F 13 ) whose Gibbs free deprotonation energies were found to be significant and comparable to the corresponding values characterizing the HTaF 6 and HSbF 5 superacids. In particular, SbF 5 /HF (i.e., HSbF 6 ) is commonly considered as the strongest known liquid superacid (exhibiting a H 0 of ca.…”