Fluoranthene salts

A typical structural feature of the crystalline radical-cation salts is the formation of stacks. Thereby, the hydrocarbon units are packed in columns leaving space for channels in which the closed-shell counterions are placed. The planar hydrocarbons are oriented perpendicularly to the stacking axes with interplanar distances between 0.32-0.33 nm which are significantly smaller than the van-der-Waals radii of the carbon centers and allow for strong w-orbital overlap. It is also characteristic that the molecules are alternately rotated by 180°, as e.g. in the fluoranthene salt [17,18]. Closed inspection shows also that a particularly strong interaction arises between r-centers which in the corresponding radical cation possess a high local spin density. 

The reaction of 2-( 1,3-dioxolan-2-yl)pyridine with 9-bromofluorene gave the quaternary salt (41%), which was cyclized in polyphosphoric acid at 110— 120°C to afford 12a-azoniabenzo [a]fluoranthene salt (250) (64JHC121). 

The difference in the electron affinity between light and heavy isotopic isomers is, in other words, the difference in the stability of their anion-radicals. Such a difference gives a valuable tool for use in probing the chemistry of anion-radicals. The difference in the stability of the ring-deuterated and ring-nondeuterated arene anion-radicals has been employed to examine the transition states for the one-electron-promoted cleavage of naphthyl methyl phenyl ether and naphthyl benzyl ether (Guthrie and Shi 1990). In this reaction, the potassium salt of fluoranthene anion-radical was an electron donor ... 

The Balz-Schiemann synthesis can be applied not only to substituted anilines but also to aminobiphcnyls1,131 or amino-substituted fused polyaromatic compounds, such as naphthalene,1114,119,129 anthracene,136 phenanthrene,1135 acenaphthene,133 fluorene,1,131,134 benzanthracene,130 136 pyrene,136 chrysene,136 fluoranthene,131 fluorenone,1,131 anthra-quinone,1,137,139,140 benzanthrone,1,117,118 phenanthraquinone,138 or xanthone.132 Fluorinated pyridines,1,141"146 methylpyridincs,126,147 149 pyridinecarboxylic acids,150 quinolines,1,151 isoquinolines,152 quinazolone,1 thiazoles,153,154 isothiazoles,156 benzothiazoles,157 thiadiazoles,155 and thiophenes154 can also be obtained from the corresponding aminated heterocycles. Modified Balz-Schiemann methods are recommended for amino nitrogen-containing heterocycles, the diazonium salts of which are rather water-soluble and unstable (a violent explosion was reported for pyridine-3-diazonium tetrafluoroborate).159 These new techniques have also been specially adapted for pyrazol-, imidazol-, or triazolamines which fail to react under classical conditions.158... 

Single crystal X-ray studies of the parent bicyclic quinolizinium and tricyclic benzoquinolizinium salts have not been reported. Two examples are available 9-phenylbenzo[b]quinolizinium salt (74) (90MI1) and 10c-azoniafluoranthene salt (246) [89AG(E)588]. In the case of planar cation 246, a significant contraction of the distances was observed around the quaternary nitrogen atom compared to fluoranthene. 

Liq Cryst 62 181 (1980) (b) W. Briitting and W. Riess Peierls Instability and Charge-Density-Wave Transport in Fluoranthene and Perylene Radical-Cation Salts Acta Phys. Pol. A 87 785 (1995). 

Fig. 1.8 Two crystals of the radical-cation salt (di-fluoranthene) hexafluorphosphate, (Fa)2PFg. The right surface of the right-hand crystal is orientated in such a way that it reflects the light coming from the light source on the right. The reflectivity is metallic due to the high conductivity of the crystal along its long axis a axis, see Fig. 2.18). The grid corresponds to 1 mm. Cf. the coloured plates in the Appendix.

Fig. 1.13 The temperature dependence of the specific electrical conductivity o of the radical-cation salt (Fa)2PFg (cf Fig. 1.8). Fa refers to fluoranthene (Fig. 1.1). At Tp = 182 K, the crystal undergoes a structural phase transition (Peierls transition). At T>Tp it behaves almost like a metal at T

There are a large number of strong CT complexes or radical-ion salts. Many organic compounds can be oxidised to radical cations by a suitable partner (e.g. perylene) or reduced to radical anions (e.g. TCNQ ".) Figure 9.12 shows a variety of such molecules. The complexes can consist of two organic molecules, as in the case of TTF-TCNQ. One of the partners can however also be an inorganic ion, e.g. Cu+ in (2,5-Dimethyl-DCNQI)2 Cu or also Ag", Li+, Cs+, Na", K+, Rb+ (see Sect. 9.5) or PF, as in the radical-cation salt (fluoranthene)J PF (see Sect. 9.6). 

In the two next sections, we wish to enter into more detail for two groups of radical-ion salts, because they demonstrate in a particularly impressive way the variety of interesting physical properties of organic metals and highly-conductive organic radical-ion salts these are the radical-ion salts with dicyanoquinone-diimine (DCNQI), already mentioned in Chap. 1 (Sect. 9.5), and the likewise previously mentioned radical-cation salts with fluoranthene (Fa) (Sect 9.6). 

The room temperature conductivity of polycrystalline samples of the naphthalene cation radical salts lies between 0.1 and 1 (Q cm) . Single crystals measured along the stack direction show a conductivity of several 100 (Q cm) depending on the quality of the crystals and to some extent on the nature of the counterions, solvent inclusion etc. The naphthalin cation radical salts can be stored for sometime at room temperature, if moisture is excluded. The corresponding radical ion complexes of perylene, pyrene, fluoranthene, and other arenes of higher number of fused rings exhibit a much greater stability and can be handled under normal laboratory conditions. 

Table 1 gives examples of some of the better investigated compounds. The fluoranthene cation radical salts have attracted the largest interest because of the ease by which they can be prepared and because of their stability and their interesting magnetic and electronic properties. ... 

Fig. 2. Projection of the crystal structure o the fluoranthene cation radical salt FA 2 6 at 298 K (a) onto the b,c-plane (b) normal to the stack axes. Data cf. V. Enkel-mann et al. ...

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