Graphite intercalation compound
Graphite intercalation compounds are intercalation compounds with a graphite host. In this type of compound the graphite layers remain largely intact and the guest molecules or atoms are located in between. When the host and the guest interact by charge transfer the in-plane electrical conductivity generally increases. When the guest forms covalent bonds with the graphite layers as in fluorides or oxides the conductivity decreases as the conjugated sp2 system collapses. In a graphite intercalation compound not every layer is necessarily occupied by guests. In so-called stage 1 compounds graphite layers and intercalated layers alternate and in stage 2 compounds two graphite layers with no guest material in between alternate with an intercalated layer. The actual composition may vary and therefore these compounds are an example of non-stoichiometric compounds. It is customary to specify the composition together with the stage.
Potassium graphite is denoted as KC8 and used as a reducing agent. It is prepared by melting potassium ( melting point 6°C) and allowing it to be absorbed by graphite. The color changes from black to bronze. Potassium graphite ignites in air and the black color is resumed. The composition can be explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework.
Examples of complex graphite intercalation compounds are those with barium and ammonia guests (Ba(NH3)2.5C10.9(st.1)) or those with cesium hydrogen and potassium (CsC8.K2H4/3C8(st.1)).
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References
- Nomenclature and terminology of graphite intercalation compounds Hanns-Peter Boehm, Ralph Setton, Eberhard stumpp Pure &Appl. Chem., Vol. 66, No. 9, pp. 1893-1901, 1994 Article