**1. Introduction**

Organic conductors have been synthesized by chemists [1,2] and their physical properties have been measured by physicists [3,4] for some time now. Chemists still now prepare many new types of organic conductors with novel structures and molecular features [5]. However, most physicists tend to continue to measure "old-fashioned" organic (super)conductors [3,4]. For example, popular salts are κ-(BEDT-TTF)2Cu(NCS)2 [6], where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene; κ-(BEDT-TTF)2Cu[N(CN)2]X (X = Cl, Br) [7,8]; θ-(BEDT-TTF)2[MM (SCN)4] (M = Cs, Rb, Tl; M = Zn, Co) [9]; α-(BEDT-TTF)2[AHg(SCN)4] (A = K, NH4) [10,11]; α-(D)2I3 (D = BEDT-TTF [12]; BETS [13], where BETS = bis(ethylenedithio)tetraselenafulvalene); and (TMTSF)2X (X = PF6, AsF6, ClO4, etc., where TMTSF = tetramethyltetrathiafulvalene) [14]. Most of these examples were first made for more than a quarter of a century ago. This may be because organic conductors prepared recently have had more complicated molecular and/or crystal structures, which are definitely interesting for chemists. However, more complication often implies bulkier molecules, which usually leads to poor conductivity. This might prevent physicists from making the measurements because of the difficulty of finding physical properties in which many physicists are interested. In this circumstance, chemists preparing simple organic conductors might be of interest, especially for physicists. Here, we report the BEDT-TTF, BEST (=bis(ethylenediseleno)tetrathiafulvalene) and BETS salts (Scheme 1) of a simple organic anion, isethionate (HOC2H4SO3 −), the structures and properties of which are reported.

**Scheme 1.** Structural formula of BEDT-TTF, BEST, BETS salts of a simple organic anion, isethionate (HOC2H4SO3 −).

#### **2. Materials and Methods**

Electrical resistivity measurements were performed by the conventional four-probe method using a HUSO HECS 994C1 four channel resistivity meter with cooling and heating rates of ≈ 0.5 K/min. The magnetic susceptibilities of polycrystalline samples of the BETS salt (**3**) were measured from 2 to 300 K using a Quantum Design MPMS-2S SQUID magnetometer. The data were corrected for a contribution from the sample holder (aluminum foil), and the sample's diamagnetic contribution was estimated from Pascal's constants. X-ray diffraction data were collected with a Rigaku Rapid II imaging plate system with a MicroMax-007 HF/VariMax rotating-anode X-ray generator with confocally monochromatic Mo*K*α radiation.

BEDT-TTF and isethionic acid sodium salt (HOC2H4SO3Na) were purchased from Tokyo Chemical Industry and Kanto Chemical, respectively, and used without any further purification. BEST and BETS were prepared according to the literature methods [15–17]. The electrocrystallisation of BEDT-TTF, BEST and BETS with HOC2H4SO3Na and 18-crown-6 ether in PhCl + 10% of EtOH produced black crystals.

The electronic states of the cationic and neutral donors and anions of **3** were calculated using the GAMESS software package [18] at the BY3LP 6-31G\* level (SBKJC core potentials for iodine) using geometries determined by the X-ray analyses. All GAMESS input options used in these calculations are shown in Supporting Information. The input files were prepared using Facio [19,20]. Population analyses were performed using the Multiwfn software package (version 3.6, Beijing Kein Research Center for Natural Science, Beijing, China) [21], which calculated Hirshfeld populations from the output files of GAMESS. The resultant point charges of all the atoms of each molecule were used for Madelung energy calculations, which were performed with the Gulp program package [22] version 5.1, with a "molecule" option to restrict the calculations to only intermolecular Coulombic repulsions; namely, the effect of intramolecular repulsions was excluded.

#### **3. Results**

Table 1 shows the crystallographic data of α-(BEDT-TTF)3(HOC2H4SO3)2 (1), β-(BEST)3(HOC2H4SO3)2·H2O (2) and α-(BETS)2(HOC2H4SO3)·H2O (3).




**Table 1.** *Cont.*

### *3.1.* α*-(BEDT-TTF)3(HOC2H4SO3)2 (1)*

α-(BEDT-TTF)3(HOC2H4SO3)2 (**1**) crystallizes in the space group *P*21/*c*. One and a half of BEDT-TTF and one isethionate are crystallographically independent. Figure 1a shows the crystal structure of **1**. The structure has alternating donor and anion layers propagating along the *a* axis. The structure of the two-dimensional conducting BEDT-TTF layer possessing an α-type packing motif is shown in Figure 1b. There are many interstack short S···S contacts, suggesting that the salt is a 2D conductor. However, the donor-to-anion ratio of 3:2 indicates that there is a BEDT-TTF trimer, in which two holes are located that form a spin dimer. Therefore, the structure suggests that the salt is a band insulator. Actually, the electrical resistivity measurements (Figure S1) indicate that the salt is a semiconductor with <sup>ρ</sup>RT = 1.15 <sup>×</sup> 10<sup>2</sup> <sup>Ω</sup>·cm and *E*<sup>a</sup> = 190 meV. The molecular arrangement of isethionate in an anionic layer is shown in Figure 1c. Intermolecular hydrogen bonding between the hydroxyl group and an oxygen atom of a nearest neighbor's sulfo group (O···O = 2.861(2) Å) forms a 1D hydrogen bond chain along the *b* axis. In addition, there is an inversion centre in the anionic layer, indicating that the anion layer is not polar.

**Figure 1.** Crystal structure (**a**); arrangement of the donor layer (**b**), where dashed lines indicate short S···S contacts (<3.7 Å); and structure of the anionic layer (**c**) of **1**.
