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) Cs-2[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).