The synthesis and vibrational spectra of fluorosulfate derivatives of titanium, zirconium and hafnium

Abstract

The syntheses of the binary fluorosulfates, Zr(SO 3F) 4 and Hf(SO 3F) 4, by oxidation of the corresponding metalpowders with bis(fluorosulfuryl) peroxide, S 2O 6F 2, in fluorosulfuric acid, HSO 3F, are described. The resulting products are white hygroscopic solids which are not sufficiently soluble in HSO 3F to allow electrical conductivity and NMR studies or Hammett acidity function ( H 0) determinations in order to evaluate their use as Lewis acids in conjugate superacid systems. Oxidation of titanium under similar conditions resulted in the formation of a greenish-yellow resin-like material of limited thermal stability with the approximate composition Ti(SO 3F) 4. However, infrared spectra indicated the presence of small amounts of HSO 3F. In addition, the solvolysis of ZrCl 4 in an excess of HSO 3F at 25 °C has been investigated as a potential route to Zr(SO 3F) 4. The results indicate that short reaction times of 1–2 d yielded incompletely substituted products of the approximate composition ZrCl x ,(SO 3F) 4−x ( x = 0.22), while prolonged reaction times of 3–4 weeks gave rise to partially decomposed materials of approximate composition ZrO 0.5F 1.5(SO 3F) 1.5. The ability of all three tetrakis(fluorosulfato) metallates to act as SO 3F − ion acceptors is evident from the isolation of thermally stable salts of the composition Cs 2[M(SO 3F) 6] (M=Ti, Zr or Hf) when the metal oxidation was carried out in the presence of 2 mol equiv. of CsSO 3F. All the materials were characterized by their vibrational spectra, which are extremely similar and closely resemble those of previously reported cesium hexakis(fluorosulfato) metallates.