An electron spin resonance study of some aryl cobalt nitroxides

Abstract

The pentacyanocobaltate(II) anion, [·Co(CN)₅]^3– reduces aromatic nitro-compounds and thereupon, behaving like a free radical, adds to aromatic nitroso-compounds to give aryl pentacyanocobalt nitroxide radical-anions, [(NC)₅Co–N(Ar)–O·]^3–, which have been characterised by their e.s.r. spectra in which the hyperfine splittings due to ¹⁴N (I= 1) and ⁵⁹Co (I= 7/2) are dominant. Several spectra have been analysed and the influence of substituents in the aromatic ring on the a_N,a_Co, and a_H splitting constants and on the g factors is discussed.

Cobalt(II)–dimethylglyoxime complexes, Co(dmg)₂XY, also react under nitrogen with aromatic nitroso-compounds and with highly chlorinated aromatic nitro-compounds to give free radicals identifiable by e.s.r. At pH 7 the cobalt(II) complex reduces ArNO to the radical (ArNHO·), at pH 8–9 there is also formed an aryl cobalt nitroxide [X(dmg)₂Co–N(Ar)–O·] for which a_N=a_Co(approx.), and at pH 12 the signal corresponds to the radical-anion (Ar–N–O·)^–.