A 19F.N.M.R. study of graphite fluorosulfates

Graphite fluorosulfates, C_nSO₃F, with n = 7 for stage-one materials, are ideally suited for ¹⁹F n.m.r. studies due to the unambiguous identity of the intercalate and its axially symmetric nature. The intensity of the signal shows a clear dependence on the orientation of the c axis with respect to the oscillating radio-frequency field H₁. The chemical shift value, however, is affected by the orientation of the c axis with respect to H₀. The powder spectrum of the stage-one material C₇SO₃F extends from 10 to 100 ppm at low temperatures, while motional narrowing at room temperature contributes to a sharp signal at the lower field end of the powder spectrum, corresponding to an axially symmetric chemical shift tensor. Angular dependence studies on C₇SO₃F samples made from HOPG indicate that the majority of the intercalated SO₃F^? ions are oriented with their molecular C₃ symmetry axes parallel to the c axis of graphite, or normal to H₀. Multi-staged samples made from HOPG demonstrate the stage dependence of the chemical shift of intercalated SO₃F^? ions. The chemical shift of the stage-one material is observed in the region of 10 – 12 ppm, while higher-staged materials show resonances at less shielded regions.