Solid-state structure and electronic states of hydrogen-bonded dimer of pyridyl-substituted tetrathiafulvalene salted with PF₆^-

Hydrogen bonding was investigated in a newly prepared salt of pyridyl-substituted tetrathiafulvalene (TTFPy) that formed a dimer structure by hydrogen bonding and was salted with PF₆^- anions, namely, (TTFPy₂H)PF₆ (1). Structural analysis of the salt by single-crystal X-ray diffraction and temperature-dependent FTIR spectra and measurements of its electrical conductivity and dielectric properties were performed. Thermal fluctuations were investigated for protons between two TTFPy molecules. An anisotropic dielectric anomaly was observed owing to local proton transfer between two pyridyl moieties. This behavior was well explained by a model of Debye-type dipole relaxation. In addition, DFT calculations showed that the dipole originated from local proton transfer, but the dipole moment in a network of TTFPy⋯H⁺⋯TTFPy dimers was amplified by a factor of 2 owing to coupling with the electronic polarization of TTFPy moieties.