Spin Density Distribution in a Nitroxide Biradical Containing 13C-Enriched Acetylene Groups in the Bridge: DFT Calculations and EPR Investigation

Abstract

A specially synthesized nitroxide biradical R₆-¹³C≡C-p-C₆H₄–C≡¹³C-R₆, B3, where R₆ = 1-oxyl-2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine nitroxide, has been studied by electron paramagnetic resonance spectroscopy, and electron-nuclear double resonance (ENDOR). Spin density distribution and hyperfine splitting (hfs) constant on ¹³C atoms calculations for biradical B3 were carried out using B3LYP and PBE0 functionals and several different basis sets including N07 family and were compared with the experimental value of the hfs constant on ¹³C atoms, measured from ENDOR spectra of B3. The mechanism of the intramolecular electron spin exchange in B3 biradical is discussed.