Positional Order and Disorder of Symmetric and Unsymmetric BEDT-STF Salts

The symmetric (s-) and unsymmetric (us-) BEDT-STF (=bis(ethylenedithio)diselenadithiafulvalene) salts were prepared, and their crystal structures and electrical resistivities were investigated. Four us-BEDT-STF salts have the positional disorder of the Se atoms in the STF framework in crystals, whereas three s-BEDT-STF salts have no disorder. When KAPPA-(us-BEDT-STF)2GaCl4 and KAPPA-(cis-s-BEDT-STF)2GaCl4 are compared, the latter without the positional disorder of the Se atoms is more conductive than the former one with the disorder.