The Fluoronium Ions H₂F^⊕ and H₃F^⊕₂: Characterization by Crystal Structure Analysis

Abstract

Two crystalline associates formed in the super‐acid system HFSbF5 have been isolated and characterized as H3F⊕2Sb2F 11⊖ 1 and H2F⊕Sb2F 11⊖. These constitute the first crystal structure determinations on fluoronium salts. The H3F 2⊕ ion of 1 contains a very strong hydrogen bridge between the two fluorine atoms and has trans conformation.

First Evidence for the Existence of Hexafluoroantimonic(V) Acid

“…[6] On the other hand, the molecular species HSbF 6 has neverbeen observed. [7] Our research group is interested in the use of Lewis superacids [8] in molecular catalysis, notably N-heterocyclic carbene gallium complexes of type [(NHC)GaX 2 ][SbF 6 ]( X=Cl, Br,I ).…”

“…[13] The antimony atoms of these identical HSbF 6 units are located on the symmetry plane of dimer 1,w hich induces some disorder ( Figure 1). [14] Nevertheless, this charge neutrala rea of the crystal lattice clearly comprises two {SbF 6 }f ragments with as hort Sb1···Sb1 (i) distance of 4.965(2) , which is only compatible with two H-bonded HSbF 6 molecules (F1···F3 (ii) distance: 2.81(3) ). The proximity of aS bF 6 À ion also suggests the existence of another hydrogen bridge (F1···F7 (ii) distance:2 .48(3) ).…”

“…(4)]. [10,11] As shown by X-ray structure analysis, two molecules of HSbF 6 were actually trapped during the crystallization of 1. [13] The antimony atoms of these identical HSbF 6 units are located on the symmetry plane of dimer 1,w hich induces some disorder ( Figure 1).…”

“…[14] Nevertheless, this charge neutrala rea of the crystal lattice clearly comprises two {SbF 6 }f ragments with as hort Sb1···Sb1 (i) distance of 4.965(2) , which is only compatible with two H-bonded HSbF 6 molecules (F1···F3 (ii) distance: 2.81(3) ). The proximity of aS bF 6 À ion also suggests the existence of another hydrogen bridge (F1···F7 (ii) distance:2 .48(3) ). The entire crystal structure in which HSbF 6 wasd etected is displayed in Figure 2.…”

“…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)].…”