An electron spin resonance study of pentacyanocobalt(III) nitroxide radical-anions from C-nitroso-compounds, nitroparaffins, and nitrolic acids (α-nitro-oximes)

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Abstract
Aqueous potassium pentacyanocobalt(II), K3Co(CN)5, reacts immediately under nitrogen with α-substituted nitrosoparaffins and more slowly with nitro-olefins and α-halogenated nitroparaffins to give alkyl pentacyanocobalt(III) nitroxide radical-anions, {(NC)5Co–NR–O·}3–, detectable by their e.s.r. spectra which are listed and discussed. These radical-anions are unstable; under nitrogen they disappear within a very few hours and rapidly on exposure to air. Simpler nitroparaffins give similar but transient spectra on treatment with K3Co(CN)5 plus NaBH4. Aqueous K3Co(CN)5 reacts rapidly with alkyl nitrites and nitric oxide, and slowly with sodium nitrite, to give red, diamagnetic {(NC)5Co–NO}3–which by reduction gives a radical-anion thought to be {(NC)5Co–N–Ō}4–. If cyanide ions are present in excess, or are added initially, alkyl nitrites and some C-nitroso-compounds yield a radical-anion thought, from its e.s.r. spectrum, to be {(NC)5Co–N(CN)–O·}3–, nitrosyl cyanide being the probable precursor. With excess of K3Co(CN)5 the α-halogenated α-nitroso- or nitro-paraffins slowly give secondary radical-anions which have larger aco hyperfine splittings than those first formed: these are stable in air. Two series of e.s.r. spectra have been obtained from nitrolic acids (α-nitro-oximes); both show splittings due to one 59Co and two 14N atoms. These radical-anions are stable in air. No e.s.r. spectra have been obtained from N-nitrosamines. E.s.r. spectra of the stable nitroxides, R2NO·, from the nitroso-compounds examined are listed.

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