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

The beta "-(BEDT-TTF)(2)CF3CH2SO3 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 beta "-( BEDT-TTF)(2)SF5CH2SO3 and beta "-(BEDT-TTF)(2)CF3CH2SO3, as well as Raman spectra of beta "-(BEDT-TTF)(2)CF3CH2SO3 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 nu(27) mode. The effect is discussed in terms of lattice dimerization involving hydrogen bonding between the anion layer and the conducting BEDT-TTF layer.