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), CS-2[PT(SO3F)(6)], AND CESIUM HEXAKIS(FLUOROSULFATO)ANTIMONATE(V),

In order to understand the reasons for the low nucleophilicity of supe racid anions, a systematic, comparative study of six superacid anions by single-crystal X-ray diffraction is undertaken. From magic acid, HS O3F-SbF5, surprisingly, single crystals of oxonium undecafluorodiantim onate(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 superaci d HSO3F. The conjugate noble metal superacid systems HSO3F-Au(SO3F)(3) and HSO3F-Pt(SO3F)(4) provide cesium tetrakis(fluorosulfato)aurate(II I) 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 syst em, HSO3F-Sb(SO3F)(5). Crystals of [H3O][Sb2F11] (1, H3F11OSb2) are or thorhombic, a = 12.744(2) Angstrom, b = 39.371(2) Angstrom, c = 11.407 (3) Angstrom, Z = 24, and space group Pbca; those of CsSO3F (2, CsFO3S ) are monoclinic, a = 7.7243(6) Angstrom, b = 8.1454(6) Angstrom, c = 7.7839(7) Angstrom, beta = 110.832(7)degrees, Z = 4, and space group P 2(1)/a; those of Cs[H(SO3F)(2)] (3, HCsF2O6S2) are monoclinic, a = 13. 371(2) Angstrom, b = 7.731(2) Angstrom, c = 9.485(2) Angstrom, beta = 128.375(7)degrees, Z = 4, and space group C2/c; those of Cs[Au(SO3F)(4 )] (4, AuCsF4O12S4) are monoclinic, a = 17.725(2) Angstrom, b = 5.822( 2) Angstrom, c = 14.624(2) Angstrom, beta = 102.120(9)degrees, Z = 4, and space group C2/c; those of CS2[Pt(SO3F)(6)] (5, Cs2F6O18PtS6) are trigonal, a = 9.070(1) Angstrom, c = 7.6028(7) Angstrom, Z = 1, space group P321; and those of Cs[Sb(SO3F)(6)] (6, CsF6O18S6Sb) are trigonal , a = 12.0317(7) Angstrom, c = 12.026(2) Angstrom, Z = 3, space group R (3) over bar. The structures were solved by Patterson (1, 2, and 6) or direct (4 and 5) methods (that of 3 is a redetermination) and were refined by full-matrix least-squares procedures to R = 0.036, 0.029, 0 .027, 0.030, 0.048, and 0.039 (R(w) = 0.032, 0.027, 0.026, 0.029, 0.04 5, and 0.037) for 4110, 2321, 1362, 1671, 738, and 1485 reflections wi th I greater than or equal to 3 sigma(F-2), for 1, 2, 3, 4, 5, and 6, respectively. in addition Cs[Sb(SO3F)(6)] is characterized by vibratio nal spectroscopy.