Metal halides, graphite-intercalated

First metal halide-graphite intercalation compound made with FeCl.i. 

Layer misfit was first recognised in the structures of two metal chloride-graphite intercalation compounds. Intercalates of graphite with many other metal halides, including fluorides and bromides, have since been reported, but they seem to be of the CC type and are not discussed here. 

The electronic character of the stacked aromatic systems makes it possible for atoms or molecules to slip between these layers, either accepting or donating electrons to bond with the carbon system, a process referred to as intercalation. Platinum metal graphite intercalates have been prepared by reducing platinum halide graphite intercalates. These catalysts are particularly useful for the selective hydrogenation of acetylenes to cis alkenes (Eqn. 9.3).22... 

The graphite-metal halides constitute the most populous group of intercalation compounds. Most of the investigative efforts have been directed towards the metal chlorides, particularly FeCls, whereas considerably less is known about the metal bromides S21). Compounds... 

At this time, no all-inclusive rule can be given that will predict whether a given compound will intercalate or not. Most of the information available seems to have been obtained empirically. Such analogies as similar chemical properties have been helpful. The many factors that infiuence the intercalation process have been surveyed by Herold (H14). In Tables II-VI are listed metal halides considered to intercalate into graphite, together with some structural information (S2J, i 9). Several general characteristics have been ascribed to intercalat-... 

Table 5.22. Transethylation of Benzene with Diethylbenzene over Graphite-Intercalated Metal Halides.112...

The presence of the potassium atoms causes the distance between the layers of carbon atoms to increase from the value of 235 pm in graphite to 540 pm in C8K. When rubidium and cesium atoms are placed between the layers, the distances between the carbon layers are 561 and 595 pm, respectively. As would be expected for materials that contain atoms of an alkali metal, these materials are extremely reactive in air, and they react explosively with water. A large number of other intercalation compounds have been prepared that have halogens, interhalogens, or metal halides as the included substances. 

This situation, clear in the case of more ionic structures, is less stringent in graphite intercalates where, presumably, there is electron transfer to (in the case of alkali-metal intercalates) or from (in the case of metal halide intercalates) the half-filled conduction bands of the graphite layers (produced by overlap of the 7t orbitals). Similarly, the periodicity requirements are less stringent for the alternating composite layers of layer silicates with complex intralayer and interlayer charge balance. 

The similarity of the two structures led Croft (15) to attempt the preparation of boron nitride intercalation compounds. He used the metal halides SbCls, SbCU, AsCU, CuCl, CuCh, FeCU, Aids, and also BF3, BCls, Br2, ICl, liquid ammonia, and N2H4. The same procedure was used as in the preparation of metal chloride-graphite compounds. 

II In that same period another type of highly reactive metal was introduced in synthetic organic chemistry graphite intercalation compounds Mg/Cg, prepared by reduction of a metal halide by potassium graphitide, K/Cg [57]. 

Biintercalation, an interleaving of different inserted species, has been studied in the case of inserted halide species " . Halogen-containing solvents, with metal chlorides, can also lead to ternary phases, such as graphite-FeCl3-C2H4Cl2 . A different approach to inserted halides is the intercalation compound with trimethyltin chloride . Finally, the intercalation of halides into carbon fibers is an area of increasing interest . ... 

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