Abstract
The oxidation of Fe(NO)~2~(CO)~2~ by tetracyanoethylene (TCNE), by the nitrosonium ion (NO^+^), or by electrolysis in polar solvents was studied by EPR spectroscopy. A number of long‐lived (τ~1/2~ of the order of hours) free radicals were detected in the early stages of reaction, all having similar isotropic g‐factors and ^14,15^N hyperfine interactions. These have been identified as the mononuclear cations, Fe(NO)~2~(CO)~2−n~St~n~^+^ (St = solvent molecule). They slowly disappear and are replaced by persistent radicals (τ~1/2~ of the order of days) that show equal isotropic hyperfine interactions with four‐, six‐ or eight‐nitrogen nuclei. Infrared and EPR spectroscopic data suggest that two of these species are trinuclear nitrosyl clusters, Fe~3~(NO)~2n~(CO) (n = 3, 4), in which the unpaired spin is localized on one iron nucleus, but which are fluxional on the EPR time‐scale. The third nitrosyl radical with four equivalent NO ligands is tentatively identified as a binuclear intermediate that may be a precursor of the trinuclear clusters.