**Hiroki Akutsu 1,\*, Yuta Koyama 1, Scott S. Turner 2, Keigo Furuta <sup>3</sup> and Yasuhiro Nakazawa <sup>1</sup>**


Received: 11 August 2020; Accepted: 28 August 2020; Published: 1 September 2020

**Abstract:** New bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)-, bis(ethylenediseleno) tetrathiafulvalene (BEST)- and bis(ethylenedithio) tetraselenafulvalene (BETS)-based organic chargetransfer (CT) salts—α-(BEDT-TTF)3(HOC2H4SO3)2 (**1**), β-(BEST)3(HOC2H4SO3)2·H2O (**2**) and α-(BETS)2(HOC2H4SO3)·H2O (**3**)—have been prepared. Salts **1** and **2** show semiconducting behaviour. Salt **3**, which is almost isostructural to α-(BETS)2I3, shows metallic behaviour down to 70 K and then shows a broader metal–insulator transition than that of α-(BETS)2I3. 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.

**Keywords:** organic conductors; bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF); bis (ethylenediseleno) tetrathiafulvalene (BEST); bis(ethylenedithio) tetraselenafulvalene (BETS); electrical resistivity; magnetic susceptibility; X-ray analysis; charge-ordered state; quantum chemical calculations; Madelung energy
