Hexafluoroarsenates of graphite from its interaction with AsF5′ AsF5+ F2′ and O2AsF6′ and the structure of C14AsF6

Abstract

The F: As molar ratio for the vacuum-stable products obtained following treatment of graphite, at room temperature, with (1) AsF_5′(2) AsF₅+ F_2′ and (3) O₂AsF_6′ has been established to be 6. X-Ray absorption spectra, in the arsenic-K pre-absorption edge region, indicate that the guest species in the vacuum-stable products via route (1) is AsF₆^–. Route (1) gives mixtures of stage-one and -two salts whereas (2) and (3) readily yield stage-one materials. This is attributed to the greater oxidizing potential of the reagents in (2) and (3). The volatiles from route (1) are AsF₅ and AsF_3′ and from (2) AsF₅. The c-axis repeat distance (i_c) of the vacuum-stable hexafluoroarsenates of formula C_14nAsF₆(where n is the stage) is ca. 7.6 + 3.35(n– 1)Å. X-Ray powder diffraction data for C₁₄AsF₆(i_c≈ 7.6 Å) indicate that the fluoride ligands of AsF₆^– are nestled in contiguous three-fold sets of carbon atom hexagons of the graphite. This requires a staggering of the enclosing carbon layers. Adjacent pairs of carbon atom sheets contain assemblies of AsF₆^– of short range order. The ordered anion arrangement is that of closest packing for nestled AsF₆^–. Aside from the restriction imposed by AsF₆^– nestling, the carbon layers are randomly stacked. In cases where the graphite galleries are richer in arsenic fluoride guests (C_xAsF_y′· 8 ⩽x < 14, 5 ⩽y⩽ 6), the i_c distances are larger (ca. 8.O Å) and the enclosing carbon layers are eclipsed.