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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 Pequation image space group. The donor sheet structure of these salts is the so-called β-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.