Structural refinement of the perfluorooctanesulfonate anion and its graphite intercalation compounds

Abstract

The optimized structure for the perfluorooctanesulfonate (PFOS) anion is obtained using hybrid density functional theory (B3LYP) with basis set 3-21G*, and indicates a helical conformation of the carbon backbone and a chain twist angle of 20°. From XRD data on a stage 2 C_xPFOS prepared from mixed hydrofluoric acid–nitric acid solution, refinement gives chain orientation (60°) and twist angles (16°). C_xPFOS samples prepared in 48% hydrofluoric acid are modeled using stage disorder, and peak width analyses indicate that these GICs correspond to solid solutions of 2nd and 3rd staging, with disorder-induced broadening increasing as the constituent stage fractions become similar in size.