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°C, monoclinic, space group P21/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°C, monoclinic, I 2/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.
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