Crystal Structures and Conducting Properties of Mott Insulator (BEDT-BDS)PF₆: Selenium Substitution Effect in the Parent (BEDT-BDT)PF₆

A new organic donor, viz. benzo[1,2-g:4,5-g′]bis(seleno[2,3-b][1,4]dithiin) (BEDT-BDS), which is a selenium analog of the parent benzo[1,2-g:4,5-g′]bis(thieno[2,3-b][1,4]dithiin), has been synthesized. The degree of “zigzag-N-shaped” molecular bending of BEDT-BDS, which is caused by the selenium substitution, is greater than that of BEDT-BDT. The N-shaped molecular bending in a radical-cation salt (BEDT-BDS)PF6 changes the S⋯S contact distances between the stacked molecules, and thus, a quasi-one-dimensional electronic structure is formed. According to the compositional formula and temperature dependence of resistivity, the PF6 salt is revealed to be a half-filled Mott insulator. A new organic donor benzo[1,2-g:4,5-g′]bis(seleno[2,3-b][1,4]dithiin) (BEDT-BDS) that is a selenium analog of the parent benzo[1,2-g:4,5-g′]bis(thieno[2,3-b][1,4]dithiin), was synthesized. The effect of selenium substitution is small in BEDT-BDS crystal but clear in its radical-cation salt (BEDT-BDS)PF6. Owing to the increase of N-shaped-molecular bending due to the heavy chalcogen substitution, intermolecular S…S contact distances became long and a quasi-one-dimensional electronic structure was formed.