Evaluation of charge transfer degree in the bis(ethylenethio)tetrathiafulvalene salts by Raman spectroscopy

Raman spectroscopy studies for a series of charge-transfer salts based on the bis(ethylenethio)tetrathiafulvalene (BET-TTF) were carried out in order to analyse the charge distribution on the donor molecules in the unit cell of crystals. With the help of the density functional theory calculations for BET-TTF0 and BET-TTF+1 molecules it was shown that the Raman spectroscopy can be applied to determine the stoichiometry in the BET-TTF salts. For salts exhibiting increase of the resistivity below ca. 100 K, the Raman spectra at variable temperature indicate that this behaviour is not related to the charge disproportionation phenomenon.