Synthesis and Characterisation of Alkali Metal and Thallium Polyfluoroantimonates, ASbnF5n+1 (n = 2, 3)

Abstract

AbstractReactions of AF (A = K, Rb, Tl) with excess liquid SbF5 in anhydrous HF (or SO2) at room temperature give products having the composition ASb2F11. The reaction between CsF and a small excess of SbF5 in anhydrous HF (0.76 mmol of CsF + 4.19 mmol of SbF5 in 4 mL of aHF) yields CsSb2F11, whereas the reaction with a large excess of SbF5 (0.79 mmol of CsF + 23 mmol of SbF5 in 10 mLof aHF) yields the salt CsSb3F16. Efforts to prepare similar compounds using the monofluorides of Li and Na led only to the already known ASbF6 compounds. Reactions of AF (A = Na, K, Rb, Cs) with liquid SbF5 at 85 °C in the absence of solvents yield the products NaSbF6, ASb2F11 (A = K, Rb) and CsSb3F16, respectively. A single‐crystal X‐ray diffraction study on the salt KSb2F11 [orthorhombic, at 250 K, Pbca, with a = 1141.65(8), b = 1279.96(9), c = 3948.5(3) pm, V = 5.7699(7) nm3 and Z = 24] has shown it to be isostructural with AgSb2F11. CsSb2F11, on the other hand, is monoclinic at 250 K [P21/n, with a = 774.10(14), b = 1425.41(17)m, c = 951.30(15) pm, β = 113.226(6)°, V = 0.9646(3) nm3 and Z = 4]. RbSb2F11 and TlSb2F11 belong to yet a third structural type. Crystals of CsSb3F16 are orthorhombic at 200 K [Pca21, with a = 2207(3), b = 772.6(11), c = 1605(3) pm, V = 2.737(8) nm3 and Z = 8]. The vibrational spectra of Sb2F11– salts are consistent with the above crystallographic assignments, showing that Sb2F11– anions deviate strongly from D4h symmetry in having no symmetry at all (point group C1). The vibrational spectra of CsSb3F16 confirm the presence of Sb3F16– anions, which adopt a cis‐fluorine‐bridged geometry consistent with the crystal structure.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)