*2.3. Electrochemical Synthesis of [Au(etdt)2]*·*THF (***2***)*

A mixture of **<sup>1</sup>** (~15 mg; 0.013 mmol) and nBu4N·PF6 (100 mg; 0.26 mmol) as a supporting electrolyte was poured into H-shaped glass cells containing Pt electrodes and dissolved in dry THF (20.0 mL). When a constant current of 0.2 μA was applied at room temperature, air-stable black needle-like single crystals with sizes less than 80 μm of **2** grew on the Pt electrode within approximately 3 weeks.

#### *2.4. Crystal Structure Determination of* **1** *and* **2**

The single-crystal X-ray diffraction data for compounds **1** and **2** were collected on a Rigaku Micro7HFM-VariMax Saturn 724R CCD system equipped with graphite monochromated Mo Kα radiation (λ = 0.71073 Å) and a confocal X-ray mirror. The crystal structures were solved using direct methods (SHELXT) [32] and refined by full-matrix least-squares (SHELXL) [33] under the Olex2 graphical interface [34]. Anisotropic temperature factors were applied for the non-hydrogen atoms. The calculated positions of the hydrogen atoms were not refined but included in the final calculations. The crystal data and experimental details of the crystal structure determination are listed in Table 1.


**Table 1.** X-ray crystallographic data of the gold complexes **1** and **2**.

<sup>1</sup> *R*<sup>1</sup> = ||*Fo*| − |*Fc*||/|*Fo*|. <sup>2</sup> *wR*<sup>2</sup> = [ ω(|*Fo*| − |*Fc*|) 2/ ω*Fo* 2] <sup>1</sup>/2.

#### *2.5. Electrical Resistivity Measurements of* **2**

Four-probe resistivity measurements were performed on compressed pellets of polycrystalline samples of **2** cooled by the liquid helium using a HECS 994C-1 multichannel four-terminal conductometer. Annealed gold wires (15 μm in diameter) bonded to the sample by gold paint were used as leads.

#### *2.6. Magnetic Measurements of* **2**

Magnetic measurements of **2** were performed with a Quantum Design MPMS-7XL superconducting quantum interference device (SQUID) magnetometer in the temperature range of 2.0−300 K. The applied magnetic field was 5000 Oe. The samples were wrapped in clean aluminum foil whose magnetic susceptibility was separately measured and subtracted. The diamagnetic contribution was estimated from Pascal's constants.

#### *2.7. Molecular Orbital, Band Structure, and Density of State Calculations of* **2**

Molecular orbital (MO), band structure, and density of state (DOS) calculations were performed by density functional theory (DFT) and the general gradient approximation (GGA) method using the DMol<sup>3</sup> module [35,36] as implemented in Materials Studio v5.5 (Accelrys, San Diego, CA, USA). Becke–Lee–Yang–Parr (BLYP) functional [37] and double numeric plus polarization (DNP) basis set were used in the calculations.

#### **3. Results and Discussion**

#### *3.1. Crystal Structure of Monoanion Gold Complex* **1**

Monoanion complex **1** crystallizes in monoclinic system with space group of *P*21/*c*. One tetra-nbutylammonium cation and one [Au(etdt)2] − anion are crystallographically independent in the unit cell. As shown in Figure 1a,b, the Au(III) atom in [Au(etdt)2] − anion shows a square-planar coordination

geometry, with Au-S distance of 2.316–2.326 Å, and an average S-Au-S angle of 91.30◦, which is similar to those of the other reported gold dithiolate complexes [13,21]. The geometry of the two etdt ligands in [Au(etdt)2] − anion is not symmetrical: One of the ligands is almost planar, while the other ligand is bent at the positions of the outermost S atoms with a dihedral angle of 50.9◦.

**Figure 1.** (**a**) Top view of the [Au(etdt)2] <sup>−</sup> anion. (**b**) Side view of the [Au(etdt)2] − anion. (**c**) Crystal structure of **1** viewed along the *b*-axis. The short S···S contacts (<3.7 Å) are shown as dotted line. The bulky tetra-n-butylammonium cations are omitted for clarity; (**d**) Crystal structure of **1** viewed along the *c*-axis.

As shown in Figure 1c, the [Au(etdt)2] − anions form side-by-side arrays along the *c*-axis with several short S···S contacts less than the sum of the van der Waals radii (<3.7 Å), with a shortest intermolecular S···S distance of 3.352 Å, indicating strong intermolecular interaction along the *c*-axis. On the other hand, the [Au(etdt)2] − anions are overlapped only on the terminal ethylene group along the long axis, to form a molecular layer parallel to the *ac* plane. As shown in Figure 1d, these molecular layers are separated by the bulky tetra-n-butylammonium cations along the *b*-axis. There is no short S···S contact between adjacent layers.
