Electronic spin structure of novel persistent neutral radical with 1,3-diazaphenalene skeleton as studied by electron-nuclear magnetic resonance spectroscopies

Novel persistent neutral π-radical with 1,3-diazaphenalene skeleton has been isolated for the first time as crystalline solids. The cw-ESR spectra of the powder sample of 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl (3) have been described by a triplet state with the spin Hamiltonian parameters of S = 1, g = 2.004, |D/hc|= 0.0167 cm -1 and |E/hc|< 10 -3 cm -1 . The temperature dependence of the triplet signal intensity was well described by a ground-state singlet dimer model with 2J/k B = -4.2 x 103 K. The similarity of the electronic structure to the parent hydrocarbon was derived from the observed parameters. The observed fine structure constants are interpreted on the basis of the two models with point dipole approximation. The degree of heteroatomic perturbation is evaluated from the π-spin density distribution obtained by local spin density functional theory.