Unstable intermediates. Part 183. An electron spin resonance study of radicals formed in irradiated sodium and potassium nitrite

Abstract

Exposure of K[NO₂] to ⁶⁰Co γ-rays at 77 K gives approximately equal yields of NO₂˙ and [NO₂˙]^2– radicals, by simple electron transfer. On annealing at >77 K the e.s.r. features characteristic of these radicals are lost, largely by recombination to give [NO₂]^– ions. However, relatively low yields of a two-nitrogen centre previously described as [N₂O₄^–] are then detected. This is stable at room temperature, and is exclusively formed on exposure at this temperature. Similar results have been obtained from Na[NO₂], except that the parallel features for [NO₂]^2– are extremely broad and hence identification is tentative. These results are discussed in the light of previous conclusions. In particular, it is suggested that the two-nitrogen species is probably [N₂O₄]^3–. The structure of this novel radical is discussed qualitatively. When the nitrites are doped with nitrate ions in low concentration the behaviour at 77 K remains unchanged, but, on annealing, [NO₃]^2– ions are formed in addition to the two-nitrogen centre. This result confirms the primary formation of [NO₂]^2– in the sodium salt and shows that the electron affinity of [NO₃]^– is greater than that of [NO₂]^–.