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Temperature dependent dc and microwave conjuctivity data together with EPR and optical reflectance measurements on the~mixedHsystem (pe)2(AsF 6)0,75(PF 6)0,35 x 0,85 CH 2 C1 2 are described. The data prove metallic behaviour of this organic solid down to 200 K.

Resume -Nalls avons etudie 1a position s pectrale et 1a form e du seuil de reflexion due au plasma da ns des sels d e ca ti o ns radicaux du type (arene}zXF, en {onction de la nature de la molecule organique donneur et du transfert de charge en tre les molecules donneur s et accepteurs.Abstract -We have inve s tigated the spectral position and the form of the plasma edge of differ en t radical cation salts o f the type (arene)zXF, in dep en den ce of the type of the organic donor molecule, and o f the charge transfer between donor and acceptor mole c ules.An important condition for the occurrence of one-dimensional metallic conduction in organic compounds is a sufficient overlap of the orbitals of adjacent molecules in the direction of the axi s of the highest conductivity. In radical cation salts, co nsisting of organic donor molecule s and inorganic acc eptor molecules, the overlap of interest is that of the donor molecules in their stacking direction. In compounds containing tetrathiafulvalene (TTF) as d o nor mole c ule, it is probably mainly the size of the sulphur atom s that contributes to this overlap /1,2/. In order to enhance this overlap not parti c ularly pronounced, one has gone two different ways. The first wa s the replacement of the sulphur by the larger selenium atom, as for in stan ce in the radi ca l cation salts which contain tetramethyltetras e lenafulvalene (THTSF) as donor molecule /3/. The other consisted in the enhancement of the number of sulphur atoms per molecule. as in the compounds with bis (ethylenedithiolo)tetrathiafulvalene (BEDT-TTF) as donor molecule / 4/.There is an entir e ly different, after the o utlin ed way of reasoning surprising. possibility for the constru c tion of one-dimensional metals. By choosing as donor molecules simple arenes. as naphthalene (Na). perylene (Pe). pyren e (Py), o r fluoranthene (Fa). one desists from the bridg e fun c tion of large atoms. as sulphur or selenium /5-7/, The metallic conduction in these compounds is apparently caused by the overlap of the o rbital s of the r ela tiv e ly small carbon atoms.In the present paper we report on o ptical investigations for the determination of the e lectronic transport parameters of thes e co mp o unds as a fun c tion o f the type of the donor molecule and of the amo unt o f charge transfer between donor and acceptor.OThis work was supported by the stiftung Volkswagenwerk

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The reflectance spectra of different radical cation salts of the type (arene)2XF6 are reported (X=P,As,Sb). For light polarised perpendicular to the molecular stacks, the crystals exhibit the optical behaviour of an insulating molecular crystal, whereas for light polarised parallel to the stacks a pronounced plasma edge is observed. Compared to other organic metals the crystals show remarkably high values of the plasma energy. Because the concentration of the free carriers is obtained from the charge transfer between the radical cations and the inorganic counter ions, the effective mass of the free carriers may be calculated from the plasma frequency. The analysis of the reflectance data by a Lorentz-Drude model yields as well the values of the mean c ollition time, the electrical conductivity, and the bandwith. +This work was supp o rted by the Stiftung Volkswagenwerk