Figure 6.

DFT calculated beta-spin energy-level comparison of 1, 2 and 3. The S 1s orbitals have been energy aligned. The ${\psi }_{\mathit{\text{LUMO}}}^{*}$ and S-S σ^* with dominant S and Cu contributions have been shown. The relative energy difference between the ${\psi }_{\mathit{\text{LUMO}}}^{*}$ and S-S σ^* are in reasonable agreement with the experimental results (see Table 2 in main text). The S-S σ^* is composed of dominantly S character. However, in the case of 2 ~7.6% Cu character is mixed. This is consistent with some back bonding interaction between the filled Cu d level and the S-S σ^*.