Compounds of graphite

There are two schools of thought as to the structure of graphite oxide. Ortho or meta ether linkages have been postulated to enforce a puckering of planes (Al), whereas a keto-enol tautomerism was suggested to keep the carbon layers planar (C3). 

With its oxygen functionality, graphite oxide has chemical properties more akin to those of layered disulfides or sheet silicates than to those of graphite (Gl, T1,A2). Many studies have been of an extremely applied nature the possibility of fluorination (LI, N1), redox potentials in the presence of hydrogen peroxide (V2), the apparent density (L2), the adsorption isotherms with nitrogen (L3), and the diffusion of Cs+ in graphite oxide (52). 

As a review on poly(carbon monofluoride) has recently appeared K1), our treatment here will be cursory. 

Made by direct combination of graphite and fluorine in the temperature range 420-630°C, carbon monofluoride is a white, nonconducting powder, chemically more similar to Teflon than to graphite. 

As with graphite oxide, there are currently two views as to the structure of carbon monofluoride. Although detailed X-ray diffraction work suggested a chair arrangement of the sp -hybridized, carbon sheets (Ml), second-moment calculations of the adsorption mode of the fluorine nuclear magnetic resonance suggested that a boat arrangement is more plausible (E2). The structures are illustrated in Fig. 3. 

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The covalent compounds of graphite differ markedly from the crystal compounds. They are white or lightly colored electrical insulators, have Hi-defined formulas and occur in but one form, unlike the series typical of the crystal compounds. In the covalent compounds, the carbon network is deformed and the carbon atoms rearrange tetrahedraHy as in diamond. Often they are formed with explosive violence. 

Historically, compounds of graphite have been placed in three categories, depending on the strength of interaction between reacting species and graphite ... 

Although the covalent compounds of graphite are thus important in their own right, they represent the extreme form of oxidative intercalation. The use of fluoride compounds to achieve highly conductive materials may ultimately lead to new forms of graphite fluoride SI). 

Fig. 4. The in-plane arrangement of a CgX network typical of many donor and acceptor compounds of graphite.

A great deal of excitement has been generated by the assertion that some intercalation compounds of graphite possess a conductivity greater than that of copper (VIO, F13, Til). Much of this work was based upon earlier researches by Ubbelohde, who found that the a-axis conductivity of the semi-metal graphite increases, and develops a me-... 

The intercalation compounds of lithium with graphite are very different in their behavior from intercalation compounds with oxides or halcogenides. Intercalation processes in the former compounds occur in the potential region from 0 to 0.4 V vs. the potential of the lithium electrode. Thus, the thermodynamic activity of lithium in these compounds is close to that for metallic lithium. For this reason, lithium intercalation compounds of graphite can be used as negative electrodes in batteries rather than the difficultly of handling metallic lithium, which is difficult to handle. 

Both of the potassium and polybromide intercalation compounds are good conductors of electricity. In the potassium inlercalam. the electrons in the conduction band can carry the current directly, as in a metal. In the compounds of graphite with polybromide. holes in the valence band conduct by the mechanism discussed previously for semiconductors (Chapter 7). 

Tatar, R. C. 1985. A theoretical study of the electronic structure of binary and ternary first stage alkali intercalation compounds of graphite. PhD Thesis, University of Pennsylvania, PA. 

The strongest similarity between ionic aromatic compounds and intercalation compounds of graphite is charge transfer. 

The strongest divergence between ionic aromatic hydrocarbons and intercalation compounds of graphite arises from variations in the ratio of peripheral carbons to internal carbons. 

Hennig, G. R. Interstitial Compounds of Graphite," in Cotton s Advances in Inorganic Chemistry, Vol. I, 125-206, Interscience Publishers, New York (1959). 

J. E. Fisher, Electronic Properties of Graphite Intercalation Compounds in Physics and Chemistry of Materials with Layered Structures, ed. F. Levy, Reidel, Dordrecht, Holland, 1977, Vol. 5, in the press L. B. Ebert and H. Selig in Abstracts of Franco-American Conference on Intercalation Compounds of Graphite, May 23—27, La Napoule, France. 

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