Reversible Intercalation of Graphite by Fluorine and Related Synthetic and Thermodynamic Studies

摘要

The pentafluorogermanate salts of a variety of cations (ClO sub 2+ , NO exp + , SF sub 3+ , NO sub 2+ , and XeF sub 5+ ) were synthesized and characterized by x-ray crystallographic and vibrational methods. The pentafluorogermanate ion was found to exist in one monomeric and at least three polymeric modifications in its salts. Lattice energy calculations and vapor pressure/temperature measurements established the following gas phase fluoride ion affinities: GeF sub 4 , 100(6); BF sub 3 , 92(6); AsF sub 5 , 115(7); XeF sub 5+ , 202(7); ClF sub 2+ , 223(7); SF sub 3+ , 211(7); IF sub 6+ , 211(7) kcal mole exp -1 . The electron affinities of the third row transition metal hexafluorides were likewise re-evaluated. The new graphite bifluorides, C sub 12+ HF sub 2- and C sub 18+ HF sub 2- , were prepared; their crystal structures establish that they are correctly formulated as graphite salts. Fluorination of graphite in the presence of HF produced these salts and the first-stage hydrofluorides C/sub x/F/sub 1-delta/(HF)/sub delta/ (5 > x > 2, x/delta approx. = 12), which were studied by XPS, NMR, vibrational spectroscopy, and crystallographic methods. In these compounds, fluorine forms weak, semi-ionic bonds to the carbon atoms, which are disposed in virtually undistorted, planar sheets. For the range of composition in which C/sub x/F/sub 1-delta/(HF)/sub delta/ is an electrical conductor (x greater than or equal to 2.3), the fluorination was found to be electrochemically reversible. (ERA citation 09:010297)