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

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 a_co 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.