Unstable intermediates. Part 146.—Electron spin resonance spectra for linear BrCN– and Br2CN radicals in irradiated cyanogen bromide crystals

Abstract

On exposure to ⁶⁰Coγ-rays at 77 K, two well defined paramagnetic centres are for med in crystalline cyanogen bromide. One, identified as BrCN^– had ⁸¹Br hyperfine and g-tensors parallel to the molecular axis and for this and other reasons is thought to be linear, with the unpaired electron in a σ* orbital largely confined to bromine and carbon. This makes an interesting contrast with the isostructural radicals FĊO and ClĊO which are reported to be strongly bent.

The other well defined radical, containing two equivalent bromine atoms, is identified as Br₂CN. A third, poorly defined radical containing two strongly coupled bromine atoms and exhibiting a large positive g-shift is tentatively identified as the cation dimer, (BrCN)⁺₂. A fourth radical, formed on exposure of solutions of cyanogen bromide in dilute solution in acetic acid to γ-rays at 77 K is tentatively identified as H(Br)CN. The structures of these new species are discussed together with possible damage mechanisms.