Combining Chirality and Hydrogen Bonding in Methylated Ethylenedithio-Tetrathiafulvalene Primary Diamide Precursors and Radical Cation Salts

Methyl- and dimethyl-ethylenedithio-tetrathiafulvalene ortho-diamide donors Me-EDT-TTF­(CONH₂)₂ (1a) and DM-EDT-TTF­(CONH₂)₂ (1b) have been prepared by the direct reaction of the corresponding diester precursors with aqueous ammonia solutions. The neutral (rac)-1a, (R)-1a, and (S,S)-1b donors have been characterized by single crystal X-ray diffraction. In the three compounds, which crystallized in the non-centrosymmetric monoclinic space group P2₁, the amide groups are disordered, yet they form the classical intramolecular hydrogen bond for such an ortho-diamide motif. Electrocrystallization experiments afforded the mixed valence radical cation salts [(S,S)-1b]₂XO₄ and [(R,R)-1b]₂XO₄ (X = Cl, Re) containing four independent donors in the asymmetric unit, with the positive charge localized essentially on two donors, while the two others are neutral. The topology of the organic layer is of β′-type. Single crystal resistivity measurements show semiconducting behavior for [(S,S)-1b]₂ClO₄ and [(R,R)-1b]₂ReO₄, with a room temperature conductivity of 5 × 10^–5 S cm^–1 and activation energies E_a ≈ 3000 K. Tight-binding band structure calculations of extended Hückel type in combination with density functional theory calculations are in agreement with the semiconducting behavior and suggest a localized Mott type semiconductor rather than a band gap semiconductor.