IR and Raman spectra of β″-(BEDT-TTF)2RCH2SO3 (R = SF5, CF3): dimerization related to hydrogen bonding

Abstract

The β″-(BEDT-TTF)₂CF₃CH₂SO₃ organic conductor has been synthesized by electrocrystallization. The crystal structure was determined by single-crystal X-ray diffraction and electronic properties examined. The polarized IR reflectance of β″-(BEDT-TTF)₂SF₅CH₂SO₃ and β″-(BEDT-TTF)₂CF₃CH₂SO₃, as well as Raman spectra of β″-(BEDT-TTF)₂CF₃CH₂SO₃ have been measured as a function of temperature. Both materials display charge-nonequivalence within the whole temperature range and unusual activation of vibronic modes with lowering the temperature. In particular, electron-molecular vibration coupling is involved in the activation of the ν₂₇ mode. The effect is discussed in terms of lattice dimerization involving hydrogen bonding between the anion layer and the conducting BEDT-TTF layer.