Unstable intermediates. Part 174. Electron spin resonance spectrum of tetraoxodinitrate(1–) formed by radiolysis of dinitrogen tetraoxide

Abstract

Exposure of crystalline N2O4 to 60Co γ-rays at 77 K gives three distinct paramagnetic centres, A, B, and C. The e.s.r. spectrum for A is characteristic of NO2˙ in a variety of subtly different sites, and that for B, which shows the presence of two equivalent nitrogen atoms, is assigned to the species [N2O4]–. The third centre, C, which is poorly defined, also contains two equivalent nitrogen atoms and is tentatively identified as [N2O4]+. Solutions of N2O4 in methanol (CD3OD) give centres A and B′. The e.s.r. parameters for B are related to those for B′, and it is suggested that they are the same species, with centre B undergoing a minor libratory motion. Theunpairedelectron in centre B ([N2O4]–) is in a σ* orbital having a smaller 2p : 2s ratio and a higher spin density on nitrogen than in the corresponding orbital of NO2, from which it is derived. It is concluded that the electron is strongly confined to the two nitrogen atoms in [N2O4]– and probably in [N2O4]+, which also appears to have a σ structure.