Radical cation salts of an unsymmetrical BEDT-TTF derivative: DIMET

Abstract

Crystal structures, temperature dependent conductivity measurements and thermopower data of several DIMET radical salts are presented and discussed.1t.'TRODUCTION A surprising fact in the structures of the organic superconductors (TMTSF)2 CI0 4 and n-(BEDT-TTF)2X (X • I). 1Bri and Aul;> is that there exists a s light dimerisation of the donor mo lecules within the stacks of these radical cation salts. Therefore, the question arises whether a more pronounced dimerisation in organic radical salts of this type leads to stronger intra-and interstack interactions and to stronger couplings between the unpaired electrons. This might result in an increase of the transition temperature to superconductivity. A step in this direction is th e preparation of "unsymmetrical" donors like DIMEI, which was synthesized recently (1-41. This new donor was electrocrystallized by us in different solvents using tetrabutylammonium salts of various anions [1,2] like CLO~, ReO~. NO;, I J . ~uI2); PF 6 , ASF~ and SbF'6 as electrolytes. With all these anions radical salts were obtained and in some cases even several crystallographic different phases. Nevertheless, i n the electrocrystallization exists the problem that solvent molecules are easily incorporated into the radical salts. Due to this inclusion of the solvent molecules metal-insultor transitions occur often already at relatively high temperatures. In order to prevent *·DIME! -4.5-Dimethyl-4' .S'-ethylenedithiolotetrathiafulvalene -CloHIOS6' 03 79.fJ 779/87/53.50