Synthesis, crystal structure, and physical property of radical cation salt of 2-(thiopyran-4-ylidene)-4,5-ethylenedithio-1,3-dithiole (TP-EDTT): (TP-EDTT)2SbF6

Electrocrystallization of 2-(thiopyran-4-ylidene)-4,5-ethylenedithio-1,3-dithiole (TP-EDTT) in an electrolytic solution containing tetrabutylammonium hexafluoroantimonate afforded black elongated platelets of (TP-EDTT)2SbF6. (TP-EDTT)2SbF6 crystallized in a triclinic system with space group P1¯: a=6.496(2), b=7.197(3), c=15.294(4) Å, α=95.58(3), β=102.09(2), γ=101.41(2)°, V=678.1(4) Å3, Z=1, and R=0.035 (I≥2σ(I)). One TP-EDTT molecule and one half SbF6 anion were crystallographically unique. TP-EDTT molecules formed a dimerized one-dimensional stacking column along the b-axis with a head-to-tail manner. Short S⋯S contacts were observed between ethylenedithio-1,3-dithiole moieties of adjacent molecules along the molecular short axis, and short S⋯F and H⋯F contacts were also observed between the thiopyran ring of TP-EDTT molecule and SbF6 anion along the molecular long axis. Tight-binding band calculation afforded the effective half-filled band structure due to the strong dimerization. The electrical resistivity showed semiconductive temperature dependence from room temperature (σRT=6.1×10−1 S cm−1, Ea=92 meV). Raman spectroscopy revealed no sign of charge disproportionation in the range from 300 to 6 K. (TP-EDTT)2SbF6 is considered to be a dimer Mott insulator.