ESR Study of High-Spin Nitrenes with s-Triazine Skeleton

Electronic and molecular structures of mononitrene 1 and bisnitrene 2 derived from 2,4,6-triazide-s-triazine 4 by photolysis have been studied by powder-pattern and single-crystal ESR spectroscopy. The experimentally determined fine-structure parameters D and E were 1.402 and 0.011 cm−1 for 1 (S = 1), and 0.280 and 0.058 cm−1 for 2 (S = 2), respectively. These values are much larger than those of phenylnitrenes (S = 1) and m-phenylenebisnitrenes (S= 2). The fine-structure parameters of bisnitrene 2 were interpreted by a semiempirical model considering dominant one-center spin-spin interactions at the monovalent nitrogen atoms, indicating that the π-electron spins are more localized on the monovalent nitrogen atoms and that the π-delocalization effect is hampered by introducing heteroatoms into the π-conjugation system