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•+ and 2•+ in solution.
EPR spectra, UV–vis absorptions, and DFT calculations show
a three-electron σ-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
σ-bond (in 1•+) and a rare example
of a persistent heteroatomic three-electron σ-bond (in 2•+).