The expansion of the carbon-carbon bond length in potassium graphites

Studies of the x-ray diffraction pattern from different potassium graphites have shown that intercalation of graphite by potassium is accompanied by an expansion of the carbon layers. This expansion is uniform within a single layer and is constant for all n carbon layers separating successive intercalate layers in the stage n compound of composition C 12 n K ( n > 1). Preferred values of the C-C bond length for stages 1 to 6, derived from the value of the a -axis parameter extrapolated to θ = 90° are: Lower accuracy in stages 3 and 6 is due to slight variation between samples, attributed to deviations from the ideal stoichiometry. Before intercalation, the C-C bond length of the pyrolytic graphite was 1·42114 (3) Å. The bond-length expansion is consistent with electron transfer from potassium to the antibonding orbitals in the upper π band of the graphitic region between successive intercalate layers. The discontinuous change of bond length with stage can be approximately represented by the relation: C-C (stage n ) = (1·4203+0·0113/ n )Å.