Intercalation of fluorine

Graphite reacts with alkali metals, for example potassium, to form compounds which are non-stoichiometric but which all have limiting compositions (for example K C) in these, the alkaU metal atoms are intercalated between the layers of carbon atoms. In the preparation of fluorine by electrolysis of a molten fluoride with graphite electrodes the solid compound (CF) polycarbon fluoride is formed, with fluorine on each carbon atom, causing puckering of the rings. 

Another point of contention has been the extent to which, if any, SbFj is reduced to SbFs upon intercalation. Although chemical analyses have shown an F Sb ratio of 5 1 (Lll, M5), Sb Mossbauer measurements (B24) indicated partial reduction of Sb(V) to Sb(III). On the other hand, mass-spectral measurements as a function of temperature (S15) showed only SbFs, evolved in stages, with no fluorocarbons emitted at any time. The latter are usually an indication of partial reduction of the intercalant and fluorination of the graphite host. Wide-line, F-NMR chemical-shifts are consistent with either SbFj or SbFe, but not with SbFs, but the occurrence of fluorine exchange could produce minor amounts of trivalent species (FI 1) this point is thus still controversial, and will be alluded to again. 

Dining interaction at ambient temperature in a bomb to produce poly (carbon monofluoride), admission of fluorine beyond a pressure of 13.6 bar must be extremely slow and carefully controlled to avoid a violently exothermic explosion [1], Previously it had been shown that explosive interaction of carbon and fluorine was due to the formation and decomposition of the graphite intercalation compound, poly (carbon monofluoride) [2], Presence of mercury compounds prevents explosion during interaction of charcoal and fluorine [3], Reaction of surplus fluorine with graphite or carbon pellets was formerly used as a disposal method, but is no longer recommended. Violent reactions observed when an exhausted trap was opened usually involved external impact on the metal trap, prodding the trap contents to empty the trap, or possibly ingress of moist air... 

In the presence of liquid HF, graphite is found to be reversibly intercalated by fluorine. First-stage materials have the composition Ci2(HF)F (l < n < 5), and the ultimate salt is the second-stage bifluoride C,2HF2. Extensive studies on these intercalates by Mallouk et al, (1985) have shown conductivities ranging from the metallic to the insulator regime. 

Examples of rod-like molecules with a branched fluorinated chain at one end (compounds 90-93) are collated in Fig. 26 [166]. It is interesting that smectic phases are retained despite the significant size of these chains. This is mainly a result of the intercalation of the aromatic cores and aliphatic spacers of these molecules, which can compensate this steric distortion. These branched chains remove the B and E phases with crystalline layers and replace them by fluid smectic phases, including SmC phases. The comparison in this figure also shows that the bulky and flexible bis(perfluoropropylene oxide) derived chains (compounds 92, 93) can provide LC materials with especially low melting points and broad mesophase ranges due to the higher conformational flexibility of perfluoroethers compared to linear perfluoroalkyl chains [99, 176]. 

During interaction at ambient temperature in a bomb to produce poly(carbon monofluoride), admission of fluorine beyond a pressure of 13.6 bar must be extremely slow and carefully controlled to avoid a violently exothermic explosion [ 1 ]. Previously it had been shown that explosive interaction of carbon and fluorine was due to the formation and decomposition of the graphite intercalation compound, poly(carbon monofluoride)... 

Katinonkul, W., Lerner, M. M., Graphite intercalation compounds with large fluoroanions. Journal of Fluorine Chemistry 2007,128, 332-335. 

FIGURE 12.28 Effects of reaction time and heat treatment on discharge characteristics of fluorine intercalated graphite fibers. (From Touhara, H., et al., Electrochim. Acta, 32, 293, 1987.)... 

Touhara H, Fujimoto H, Kadono K, Watanabe N, Endo M. Electrochemical characteristics of fluorine intercalated graphite fiber-lithium cells. Electrochim Acta 1987 32 293-298. 

Fig. 2. DSC curves of fluorine-intercalated carbon fibers (Stage 2+1 C4 9F and Stage 1 C3F) in nitrogen atmosphere (heating rate 5 K min 1) (reproduced with permission from Synth. Metals, 73 (1995) 69 [19]).

Fig. 3. Room temperature F NMR spectra of fluorine-intercalated graphite at 282.4 MHz. In addition to an intensive broad line in the range between —30, —270 ppm, weak broad peaks around 5 0 ppm (shown in inset) exist for some fluorinated compounds the fine structure is not pronounced (reproduced with permission from J. Phys. Condens. Matter, 10 (1998) 7633 [24]).

New aspects on the electrochemical behavior of fluorine-intercalated graphite... 

Discharge characteristics of fluorine-graphite intercalation compounds... 

Other metal fluoride intercalation compounds can be formed in the presence of fluorine, where the formation of MF +i complexes from MF adds to the overall stability. Examples include the intercalation of WFe and ReFe in the presence of F2 via formation of MFv guest species, CgMFg (M = P, As), and C Bp4 compounds. Direct intercalation of AsFs occurs by a different mechanism (see below). Metal chlorides react similarly. Thus AICI3 and NiCh can form intercalation compounds in the presence of CI2 through formation of the complex anions AlCLt, NiCl3, or NiCLi. ... 

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