Spectroscopic investigations of the BEDT-TTF charge transfer salts with NO3− anions (β″- and δ-phase)

We report the polarized reflectance spectra (650-6500 cm−1) as well FT-NIR Raman spectra of β″-(BEDT-TTF)3(NO3)2 and δ-(BEDT-TTF)2(NO3)0.9(NO2)0.1 salts as a function of temperature. Additionally, the crystal structure of δ-phase salt was determined at room temperature and the temperature dependence of electrical conductivity was measured. The reflectance spectra of metallic β″-phase salt were fitted with the Drude model; the metal-insulator transition at T = 20-27 K has practically no influence on IR spectra. The δ-phase salt shows semiconducting behavior; inside conducting organic layers the BEDT-TTF molecules are arranged in dimers. The specific vibrational features of the δ-salt are discussed in terms of hydrogen bonding between BEDT-TTF and anions.