Infrared and Raman studies of the kappa-phase charge-transfer salts formedby BEDT-TTF and magnetic anions M(CN)(6)(3-) (where M = Co-III, Fe-III, Cr-III)

The isostructural charge-transfer salts kappa-[Et4N](BEDT-TTF)(4)M(CN)(6). 3H(2)O (M = Co-III, Fe-III, Cr-III) are organic semiconductors undergoing t wo intriguing phase transitions at T = 240 and 150K. Polarized IR reflectan ce spectra (from 650 to 6500 cm(-1)) of these compounds were studied at roo m temperature. An electronic dispersion in IR spectra was analyzed in terms of a Drude-Lorentz model and optical transport parameters were determined. IR reflectance spectra of Fe-III crystals were measured in the temperature range from 190 to 300K and the influence of the phase transition at 240K w as studied. We report also FT-NIR Raman studies of Fe-III salt as a functio n of temperature from 110 to 300K. The Raman line related to the nu (3)(A(g )) C=C mode of BEDT- TTF splits below 240K into three components providing evidence of charge redistribution in the BEDT-TTF layers.