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 (12·FeBr4 and 12·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 12·FeBr4 and 12·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 12·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 π spin of 1.