Superacid Anions: Crystal and Molecular Structures of Oxonium Undecafluorodiantimonate(V), [H3O][Sb2F11], Cesium Fluorosulfate, CsSO3F, Cesium Hydrogen Bis(fluorosulfate), Cs[H(SO3F)2], Cesium Tetrakis(fluorosulfato)aurate(III), Cs[Au(SO3F)4], Cesium Hexakis(fluorosulfato)platinate(IV), Cs2[Pt(SO3F)6], and Cesium Hexakis(fluorosulfato)antimonate(V), Cs[Sb(SO3F)6]

In order to understand the reasons for the low nucleophilicity of superacid anions, a systematic, comparative study of six superacid anions by single-crystal X-ray diffraction is undertaken. From magic acid, HSO3F−SbF5, surprisingly, single crystals of oxonium undecafluorodiantimonate(V), [H3O][Sb2F11], 1, are obtained. In the remaining five salts the cesium ion, Cs+, is used as the countercation. Both CsSO3F, 2, and its solvate Cs[H(SO3F)2], 3, are derived from the Bronsted superacid HSO3F. The conjugate noble metal superacid systems HSO3F−Au(SO3F)3 and HSO3F−Pt(SO3F)4 provide cesium tetrakis(fluorosulfato)aurate(III) Cs[Au(SO3F)4], 4, and cesium hexakis(fluorosulfato)platinate(IV) Cs2[Pt(SO3F)6], 5. Cesium hexakis(fluorosulfato)antimonate(V) Cs[Sb(SO3F)6], 6, whose synthesis is described here in detail, provides evidence for the possible existence of a new conjugate superacid system, HSO3F−Sb(SO3F)5. Crystals of [H3O][Sb2F11] (1, H3F11OSb2) are orthorhombic, a = 12.744(2) A, b = 39.371(2) A, c = 11.407(...