POLARIZABILITIES OF THE INTERMOLECULAR CONTACTS IN BEDT-TTF AND BEDO-TTF MOLECULAR-CRYSTALS

In BEDT-TTF and BEDO-TTF molecular crystals the indicatrix orientation , the optic axes angle, the birefringence, and the absorption tensor w ere measured in the VIS and NIR spectral range. The principal refracti ve indices and the corresponding optical axes have been calculated by tensorial addition of the bond polarizabilities of all bonds in the mo lecules. Moreover calculations with relative polarizibilities were car ried out. Comparing the calculated and the measured values shows that the polarizabilities of the molecules only can not yield the measured indicatrix and axes angle. Polarizabilities with other orientations mu st be involved. Therefore the crystal structures have been examined. I n BEDT-TTF ten, and in BEDO-TTF four different contacts between the mo lecules exist with contact distances lower than the van der Waals dist ances. Assigning polarizabilities to these contacts can explain the me asured behaviour. The absorption spectra confirm the intermolecular in teraction.