After effects of the cobalt-57–iron-57 electron-capture reaction in hexacyanocobaltate(III) complexes

Abstract

Isomorphous hexacyanocobaltate(III) complexes with the bivalent metal cations Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺ have been labelled with ⁵⁷Co and used as Mössbauer sources. Whilst the spectrum of the complex Fe₃[⁵⁷Co(CN)₆]₂ can be resolved into a single line corresponding to the ion Fe^II(CN)₆^4– and a doublet, those of all the other sources result in two doublets, of which one corresponds to the ion Fe^III(CN)₆^3–. The extra doublet in these spectra shows that the ⁵⁷Co–⁵⁷Fe electron-capture reaction gives rise to the formation of a new ⁵⁷Fe labelled species, tentatively identified as a pentacyanide ion. The relative yield of the new species decreases with increasing ionization energy for the divalent cation. This can be understood by assuming that the observed chemical effects are due to Auger cascades followed by Coulomb fragmentation; if, however, the charge relaxation is sufficiently rapid, such fragmentation may be prevented.