Synthesis and Characterisation of Alkali Metal and Thallium Polyfluoroantimonates, ASb n F 5 n +1 ( n = 2, 3)

Reactions of AF (A = K, Rb, Tl) with excess liquid SbF 5 in anhydrous HF (or SO 2 ) at room temperature give products having the composition ASb 2 F 11 . The reaction between CsF and a small excess of SbF 5 in anhydrous HF (0.76 mmol of CsF + 4.19 mmol of SbF 5 in 4 mL of aHF) yields CsSb 2 F 11 , whereas the reaction with a large excess of SbF 5 (0.79 mmol of CsF + 23 mmol of SbF 5 in 10 mLof aHF) yields the salt CsSb 3 F 16 . Efforts to prepare similar compounds using the monofluorides of Li and Na led only to the already known ASbF 6 compounds. Reactions of AF (A = Na, K, Rb, Cs) with liquid SbF 5 at 85 °C in the absence of solvents yield the products NaSbF 6 , ASb 2 F 11 (A = K, Rb) and CsSb 3 F 16 , respectively. A single‐crystal X‐ray diffraction study on the salt KSb 2 F 11 [orthorhombic, at 250 K, Pbca , with a = 1141.65(8), b = 1279.96(9), c = 3948.5(3) pm, V = 5.7699(7) nm 3 and Z = 24] has shown it to be isostructural with AgSb 2 F 11 . CsSb 2 F 11 , on the other hand, is monoclinic at 250 K [ P 2 1 / n , with a = 774.10(14), b = 1425.41(17)m, c = 951.30(15) pm, β = 113.226(6)°, V = 0.9646(3) nm 3 and Z = 4]. RbSb 2 F 11 and TlSb 2 F 11 belong to yet a third structural type. Crystals of CsSb 3 F 16 are orthorhombic at 200 K [ Pca 2 1 , with a = 2207(3), b = 772.6(11), c = 1605(3) pm, V = 2.737(8) nm 3 and Z = 8]. The vibrational spectra of Sb 2 F 11 – salts are consistent with the above crystallographic assignments, showing that Sb 2 F 11 – anions deviate strongly from D 4 h symmetry in having no symmetry at all (point group C 1 ). The vibrational spectra of CsSb 3 F 16 confirm the presence of Sb 3 F 16 – anions, which adopt a cis ‐fluorine‐bridged geometry consistent with the crystal structure.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)