Sulfamoyl nitrenes: singlet or triplet ground state?

Area of Science:

• Chemical Physics
• Theoretical Chemistry
• Spectroscopy

Background:

• Alkyl- and aryl-sulfonylnitrenes typically exhibit a triplet spin-state.
• Theoretical computations predicted a closed-shell singlet (CSS) ground state for simple sulfamoylnitrenes (R2NS(O)2-N) due to intramolecular nitrogen-nitrogen interactions.

Purpose of the Study:

• To experimentally investigate the ground state spin-state of simple sulfamoylnitrenes.
• To reconcile theoretical predictions with experimental observations regarding sulfamoylnitrene spin states.

Main Methods:

• Generation of sulfamoylnitrenes via laser photolysis of corresponding azides.
• Characterization of the generated species using Electron Paramagnetic Resonance (EPR) spectroscopy at 5 K.
• Analysis of vibrational modes using Infrared (IR) spectroscopy at 3 K.

Main Results:

• Experimentally, both sulfamoylnitrenes (R = H and Me) were isolated in the triplet state.
• Electron Paramagnetic Resonance (EPR) and Infrared (IR) spectroscopy confirmed the triplet spin-state at cryogenic temperatures.
• Theoretical calculations suggest the formation of the higher-energy triplet state from an initially generated CSS state via a minimum energy crossing point (MECP).

Conclusions:

• Sulfamoylnitrenes exist in the triplet state under experimental conditions, contrary to initial theoretical predictions of a singlet ground state.
• A spin-state change from closed-shell singlet (CSS) to triplet is proposed to occur through a minimum energy crossing point (MECP).
• Intramolecular nitrogen-nitrogen interactions play a crucial role in the electronic structure and spin-state determination of sulfamoylnitrenes.