Graphite intercalation compound
In the area of
Preparation and structure
These materials are prepared by treating graphite with a strong oxidant or a strong reducing agent:
- C + m X → CXm
The reaction is reversible.
The host (graphite) and the guest X interact by
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. The layers are pushed apart upon incorporation of the guest ions.
Examples
Alkali and alkaline earth derivatives
One of the best studied graphite intercalation compounds, KC8, is prepared by melting
- 3 KC8 → KC24 + 2 K
Via the intermediates KC24 (blue in color),[3] KC36, KC48, ultimately the compound KC60 results.
The stoichiometry MC8 is observed for M = K, Rb and Cs. For smaller ions M = Li+, Sr2+, Ba2+, Eu2+, Yb3+, and Ca2+, the limiting stoichiometry is MC6.
With barium and ammonia, the cations are solvated, giving the stoichiometry (Ba(NH3)2.5C10.9(stage 1)) or those with caesium, hydrogen and potassium (CsC8·K2H4/3C8(stage 1)).[clarification needed]
In situ adsorption on free-standing graphene and intercalation in bilayer graphene of the alkali metals K, Cs, and Li was observed by means of low-energy electron microscopy.[7]
Different from other alkali metals, the amount of Na intercalation is very small. Quantum-mechanical calculations show that this originates from a quite general phenomenon: among the alkali and alkaline earth metals, Na and Mg generally have the weakest chemical binding to a given substrate, compared with the other elements in the same group of the periodic table.[8] The phenomenon arises from the competition between trends in the ionization energy and the ion–substrate coupling, down the columns of the periodic table.[8] However, considerable Na intercalation into graphite can occur in cases when the ion is wrapped in a solvent shell through the process of co-intercalation. A complex magnesium(I) species has also been intercalated into graphite.[9]
Graphite bisulfate, perchlorate, hexafluoroarsenate: oxidized carbons
The intercalation compounds graphite bisulfate and graphite perchlorate can be prepared by treating graphite with strong oxidizing agents in the presence of strong acids. In contrast to the potassium and calcium graphites, the carbon layers are oxidized in this process:
- 48 C + 0.25 O2 + 3 H2SO4 → [C24]+[HSO4]−·2H2SO4 + 0.5 H2O[clarification needed]
In graphite perchlorate, planar layers of carbon atoms are 794 picometers apart, separated by ClO−4 ions. Cathodic reduction of graphite perchlorate is analogous to heating KC8, which leads to a sequential elimination of HClO4.
Both graphite bisulfate and graphite perchlorate are better conductors as compared to graphite, as predicted by using a positive-hole mechanism.[4] Reaction of graphite with [O2]+[AsF6]− affords the salt [C8]+[AsF6]−.[4]
Metal halide derivatives
A number of metal halides intercalate into graphite. The chloride derivatives have been most extensively studied. Examples include MCl2 (M = Zn, Ni, Cu, Mn), MCl3 (M = Al, Fe, Ga), MCl4 (M = Zr, Pt), etc.[1] The materials consists of layers of close-packed metal halide layers between sheets of carbon. The derivative C~8FeCl3 exhibits spin glass behavior.[10] It proved to be a particularly fertile system on which to study phase transitions.[citation needed] A stage n magnetic graphite intercalation compounds has n graphite layers separating successive magnetic layers. As the stage number increases the interaction between spins in successive magnetic layers becomes weaker and 2D magnetic behaviour may arise.
Halogen- and oxide-graphite compounds
Chlorine and bromine reversibly intercalate into graphite. Iodine does not. Fluorine reacts irreversibly. In the case of bromine, the following stoichiometries are known: CnBr for n = 8, 12, 14, 16, 20, and 28.
Because it forms irreversibly, carbon monofluoride is often not classified as an intercalation compound. It has the formula (CF)x. It is prepared by reaction of gaseous fluorine with graphitic carbon at 215–230 °C. The color is greyish, white, or yellow. The bond between the carbon and fluorine atoms is covalent. Tetracarbon monofluoride (C4F) is prepared by treating graphite with a mixture of fluorine and hydrogen fluoride at room temperature. The compound has a blackish-blue color. Carbon monofluoride is not electrically conductive. It has been studied as a cathode material in one type of primary (non-rechargeable) lithium batteries.
Graphite oxide is an unstable yellow solid.
Properties and applications
Graphite intercalation compounds have fascinated materials scientists for many years owing to their diverse electronic and electrical properties.
Superconductivity
Among the superconducting graphite intercalation compounds, CaC6 exhibits the highest
Reagents in chemical synthesis: KC8
The bronze-colored material KC8 is one of the strongest
See also
- Buckminsterfullerene intercalates
- Covalent superconductors
- Magnesium diboride, which uses hexagonal planar boron sheets instead of carbon
- Pyrolytic graphite
References
- ^ ISBN 978-0-08-037941-8.
- S2CID 98227391. Archived from the original(PDF) on 2012-04-06.
- ^ ISSN 0008-6223.
- ^ ISBN 978-0-13-175553-6.
- ^ NIST Ionizing Radiation Division 2001 – Major Technical Highlights. physics.nist.gov
- ^ PMID 27878015.
- PMID 29733660.
- ^ PMID 27001855.
- S2CID 49412174.
- .
- ^ S2CID 6764457.
- ^ PMID 17477336.
Further reading
- T. Enoki, M. Suzuki and M. Endo (2003). Graphite intercalation compounds and applications. Oxford University Press. ISBN 978-0-19-512827-7.
- S2CID 123597602.
- D. Savoia; Trombini, C.; Umani-Ronchi, A.; et al. (1985). "Applications of potassium-graphite and metals dispersed on graphite in organic synthesis" (PDF). Pure and Applied Chemistry (PDF). 57 (12): 1887. S2CID 95591721.
- Suzuki, Itsuko S.; Ting-Yu Huang; Masatsugu Suzuki (13 June 2002). "Magnetic phase diagram of the stage-1 CoCl2 graphite intercalation compound: Existence of metamagnetic transition and spin-flop transitions". Physical Review B. 65 (22): 224432. .
- Rancourt, DG; C Meschi; S Flandrois (1986). "S=1/2 antiferromagnetic finite chains effectively isolated by frustration: CuCl2-intercalated graphite". Physical Review B. 33 (1): 347–355. PMID 9937917.