Graphite intercalation compound
From Wikipedia, the free encyclopedia
Graphite intercalation compounds are intercalation compounds with a graphite host [1] [2] [3]. 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 is one of the strongest reducing agents known. It is prepared under inert atmosphere by melting potassium over graphite powder. The potassium is absorbed into the graphite and a color change from black to bronze is observed. The resulting solid is also quite pyrophoric. Structurally, composition can be explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between graphite and potassium atoms is ionic and the compound is electrically conductive. [4].
Potassium graphite has also been used as a catalyst in polymerizations and as a coupling reagent for aryl halides to biphenyls [5].
In one study [5] freshly prepared KC8 is treated with 1-iodododecane delivering a modification (micrometre scale carbon platelets with long alkyl chains sticking out providing solubility) that is soluble in chloroform. Another potassium graphite compound, KC24, has been used as a neutron monochromator.
Carbon monofluoride is denoted as (CF)x and used as a cathode material in a type of lithium batteries. It is prepared by reaction of gaseous fluorine with graphitic carbon at 420-450 °F. The color is grayish, white, or yellow. The bond between the carbon and fluorine atoms is covalent. The compound is not electrically conductive.
Tetracarbon monofluoride is denoted as C4F. It is prepared by reacting gaseous fluorine mixed with hydrogen fluoride with graphite at room temperature. The compound has blackish-blue color.
Other examples are graphite bisulfate and graphite oxide.
Examples of complex graphite intercalation compounds are those with barium and ammonia guests (Ba(NH3)2.5C10.9(st.1)) or those with caesium, hydrogen and potassium (CsC8.K2H4/3C8(st.1)).
[edit] External links
[edit] References
- ^ For a review, see Intercalation compounds of graphite, M.S. Dresselhaus and G. Dresselhaus, Advances in Physics, Vol. 30, pp. 139-326, 1981, also reprinted as Advances in Physics, Vol. 51, pp. 1-186, 2002.
- ^ 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
- ^ Applications of potassium-graphite and metals dispersed on graphite in organic synthesis Diego Savoia, Claudio Trombini, Achille Umani—Ronchi Pure & Appl. Chem., Vol. 57, No. 12, pp. 1887—1896, 1985 Article
- ^ NIST Ionizing Radiation Division 2001 - Technical Highlights
- ^ a b Functionalization of Potassium Graphite, Soma Chakraborty, Jayanta Chattopadhyay, Wenhua Guo, and W. Edward Billups Angew. Chem. Int. Ed. 2007, 46, 4486 –4488 doi:10.1002/anie.200605175
