Unstable intermediates. Part LXXIX. Electron spin resonance studies of the effect of environment upon the hyperfine parameters for CO2– and NO2

Abstract

Exposure of alkali and alkaline-earth metal formates to ⁶⁰Co γ-radiation gave e.s.r. spectra characteristic of CO₂^– radicals. These results are compared with those previously published for CO₂^– in various matrices and with a range of results for NO₂ in different environments. Both radicals rotate or librate extensively, but after these movements have been quenched or allowed for, the effect of the environment upon the spin-density distributions and 2p/2s could be gauged. The results for CO₂^– were markedly dependent upon the nature of the host lattice, but those for the isoelectronic NO₂ radical were almost independent of environment. This difference is presumed to be a result of the negative charge of the former radical and of the consequent large crystal fields that it experiences.

The e.s.r. spectra of γ-irradiated alkali-metal formates exhibit well resolved hyperfine coupling to the cation nuclei. Trends in the spin-densities derived therefrom are discussed.