Odd-Electron-Bonded Sulfur Radical Cations: X-ray Structural Evidence of a Sulfur-Sulfur Three-Electron σ-Bond

The one-electron oxidations of 1,8-chalcogen naphthalenes Nap(SPh)(2) (1) and Nap(SPh)(SePh) (2) lead to the formation of persistent radical cations 1(center dot+) and 2(center dot+) in solution. EPR spectra, UV-vis absorptions, and DFT calculations show a three-electron sigma-bond in both cations. The former cation remains stable in the solid state, while the latter dimerizes upon crystallization and returns to being radical cations upon dissolution. This work provides conclusive structural evidence of a sulfur-sulfur three-electron sigma-bond (in 1(center dot+)) and a rare example of a persistent heteroatomic three-electron sigma-bond (in 2(center dot+)).