| Summary: | New bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)-, bis(ethylenediseleno)tetrathiafulvalene (BEST)- and bis(ethylenedithio)tetraselenafulvalene (BETS)-based organic charge-transfer (CT) salts—α-(BEDT-TTF)<sub>3</sub>(HOC<sub>2</sub>H<sub>4</sub>SO<sub>3</sub>)<sub>2</sub> (<b>1</b>), β-(BEST)<sub>3</sub>(HOC<sub>2</sub>H<sub>4</sub>SO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O (<b>2</b>) and α-(BETS)<sub>2</sub>(HOC<sub>2</sub>H<sub>4</sub>SO<sub>3</sub>)·H<sub>2</sub>O (<b>3</b>)—have been prepared. Salts <b>1</b> and <b>2</b> show semiconducting behaviour. Salt <b>3</b>, which is almost isostructural to α-(BETS)<sub>2</sub>I<sub>3</sub>, shows metallic behaviour down to 70 K and then shows a broader metal–insulator transition than that of α-(BETS)<sub>2</sub>I<sub>3</sub>. The reason for the difference in behaviour is estimated by the comparison of the Madelung energies of the full set of patterns of possible donor’s charge-ordered and anion’s disordered states.
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