Fig. 1: Schematic representation of odd-electron σ-bonds and selected examples.

a The B·B one-electron σ–bond proved by EPR. b The B·B one-electron σ–bond proved by X-ray diffraction. c The P·P one-electron σ–bond. d The Cu·B heteronuclear one-electron σ–bond. e The Xe·Xe one-electron σ–bond. f The N∴N three-electron σ–bond. g The S∴S and Se∴Se three-electron σ–bonds. h The Pd∴Pd and Ni∴Ni three-electron σ–bonds. i The Rh∴Si and Ir∴Si heteronuclear three-electron σ–bonds.