Metallic conductivity and ferromagnetic interaction of iron(III) d spins in the needle crystals of (ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)2•FeBr4 salt

The 2:1 charge-transfer (CT) salts (1(2).FeBr4 and 1(2).GaBr4) of ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr4- and GaBr4- counteranions were obtained as needle crystals, whose structures are almost the same as each other. The 1 molecules form a one dimensionally stacked column with alternation of their molecular axis direction, while the counteranions are aligned in parallel with the 1-stacked columns with the direction of their distorted-tetrahedral geometry maintained. The room-temperature electrical conductivities measured on the single crystals of 1(2).FeBr4 and 1(2).GaBr4 were 4.6 and 2.1 S cm(-1), respectively. From the temperature dependences of their electrical conductivities in both cases the electrical conducting properties were metallic between ca. 170 and 300 K, but below ca. 170 K converted to be semiconducting and continued till 5 K, although the activation energies are very small (4-10 meV). For 1(2).FeBr4 very weak and antiferromagnetic interaction occurred between the d spins of FeBr4- ions in the temperature range of ca. 1-300 K. However, below ca. 15 K the ferromagnetic interaction was reversely preferential possibly by participation of the pi spin of 1.