Molecular Conductors with Effectively Half-Filled Electronic States Based on Tetrathiafulvalene Derivatives Condensed with a 2-Isopropylidene-1,3-dithiole Ring

The electron donor 2-isopropylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene (3) provides two new molecular conductors, (3)(2)[M(CN)(2)] (M = Ag and Au). These salts crystallize in the triclinic P (1) over bar space group. The donor sheet structure of these salts is the so-called beta-type molecular array, in which the donor molecules form a head-to-tail dimer. The formation of considerable dimerization and the 2:1 donor-anion ratio result in an effectively half-filled electronic nature. These salts show metallic conducting behavior from room temperature. The metallic conducting behavior of (3) (2)[Ag(CN)(2)] was retained down to 8 K; however, the resistivity of (3)(2)[Au(CN)(2)] increased at around 50 K. The magnetic susceptibility of (3)(2)[Au(CN)(2)] suggests that the strength of the electron correlation for this salt is enhanced below 50 K.