A diradical based on odd-electron σ-bonds

Area of Science:

• Inorganic Chemistry
• Theoretical Chemistry
• Materials Science

Background:

• Odd-electron bonds, including one-electron and three-electron sigma bonds, are crucial intermediates in various chemical processes.
• Stable diradicals, characterized by unpaired electrons, are typically based on localized s/p orbitals or delocalized pi systems.
• The isolation of diradicals specifically based on odd-electron sigma bonds has remained an elusive goal in chemistry.

Purpose of the Study:

• To report the synthesis and characterization of a novel dication diradical stabilized by three-electron selenium-selenium sigma bonds.
• To investigate the electronic structure and bonding in this unique diradical species.
• To compare the behavior of the selenium-based diradical with its sulfur analogue.

Main Methods:

• Computational chemistry calculations to model the electronic structure and bonding.
• Spectroscopic techniques for characterization.
• Synthesis of selenium and sulfur dication compounds.

Main Results:

• A stable dication diradical featuring two Se∴Se three-electron sigma bonds was successfully synthesized and characterized.
• The electronic structure confirms the diradical nature arising from these unique odd-electron bonds.
• The analogous sulfur dication exhibited closed-shell singlet behavior, lacking diradical character.

Conclusions:

• This work presents the first definitive example of a diradical stabilized by odd-electron sigma bonds, specifically using selenium.
• The findings expand the known structural motifs for stable diradicals.
• The contrasting behavior between the selenium and sulfur analogues highlights the unique role of heavier chalcogens in stabilizing unusual bonding arrangements.