Structures and electrical properties of molecular conductors based on bis-fused TTF donors with bis(alkylthio) groups

Several bis(alkyldithio) derivatives of BDT-TTP (BTCn-TTP), where BDT-TTP is 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, have been synthesized. Cyclic voltammograms of new donors consist of four pairs of single-electron transfer waves, and the first redox potentials (E1) are higher by 0.04-0.05 V than that of unsubstituted BDT-TTP. The TaF6- salt of bis(methylthio) derivative (BTM-TTP) have the so-called β-type array of the donors. A tight-binding band calculation of (BTM-TTP)2TaF6 suggests that this salt has a quasi one-dimensional Fermi surface. The BTM-TTP salts with the PF6- and TaF6- anions exhibit metallic temperature dependence down to 90 K, while the SbF6- salt is a semiconductor with the activation energy of 0.13 eV.