CRYSTAL-CHEMISTRY OF SUPERACIDS - FORMATION AND STRUCTURE OF THE LOW-MELTING ADDUCTS SBF5.CF3SO3H AND SBF5.7HF[1]

The melting diagram of the superacid system SbF5-CF3SO3H as well as of SbF5-HF has been studied by DTA and the crystal structure of one newly found low-melting adduct in each case determined. The adduct SbF5.CF3SO3H (m.p. - 1-degrees-C, monoclinic, space group P2(1)/c, Z = 4 formula units per unit cell) is composed of complex molecules F5SbOS(CF3)(O)OH which are linked by strong hydrogen bonds O-H...F to infinite chains. The adduct SbF5.7HF (melting incongruently at -75-degrees-C, monoclinic, I2/m, Z = 2) is a fluoronium salt, (H7F6)SbF6. The novel H7F6+ cation is formed as an unbranched chain by very strong hydrogen bonds between the respective F atoms, which become weaker from the center to the ends. A further hydrogen bond of this kind, between the cations and the octahedral SbF6-anions, again leads to a one-dimensional polymer.