Structural aspects of the phase transitions in (BEDO-TTF)(2)ReO4 center dot H2O

The effect of the first-order phase transition occurring around 220K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF )(2)ReO4. H2O has been studied. The crystal structure at 170K has been dete rmined and it is found that the main structural change resulting from the p hase transition is connected with a rotation of the ReO4- anions. This rota tion leads to changes in the S .... S and S ... O intermolecular contacts w ithin the BEDO-TTF donor layers, nevertheless the band structure is remaine d practically unchanged Possible changes in the crystal structure which can occur at room temperature depending on the experimental conditions are con sidered. It seems very likely that the (BEDO-TTF)(2)ReO4. H2O crystal loses its water molecules in the vacuum and hence changes its crystal structure.