Suppression of a Structural Phase Transition by an Orientational Disorder of Counteranions in an Organic Conductor, β″-β″-(BEDT-TTF)ClCHSO.

In 2022, we reported that the β″-(BEDT-TTF)ClCHSO salt () has a phase transition at 210 K on cooling and 260 K on heating, which was suggested as a nondoped-to-doped transition. During the synthesis of , a second salt was coproduced, the structure and properties of which are reported here. The new salt β″-β″-(BEDT-TTF)ClCHSO () has the same composition and is isomorphous to , the low-temperature phase of . However, the salt shows no phase transition. , the high-temperature phase of , displays rotational disorders of the -SO groups. In contrast, the anions in have no rotational disorders but have orientational disorders. Approximately 13% of the anions in have their orientation as opposed to the remaining anions. The geometrically calculated shortest O···O distance is 2.24 Å if neighbor -SO groups are able to rotate freely. This is 1.1 Å shorter than the sum of the van der Waals radii, and therefore, this is too close to allow free rotation. Therefore, it is proposed that has no rotational disorder, which leads to no phase transition as is observed in .