Paramagnetic transition-metal carbonyls and cyanides. Part 9. An electron spin resonance study of the radiolysis of some iron carbonyls : the anions [Fe(CO)5]– and [Fe(CO)4]–

Abstract

Exposure of dilute solutions of [Fe(CO)5] in 2-methyltetrahydrofuran to 60Co γ-rays at 77 K resulted in electron addition to give species A. On annealing, this rapidly decomposed to give species B, which was stable up to the softening point of the glass. Irradiation of Na2[Fe(CO)4] at 77 K gave directly species B, which is therefore identified as [Fe(CO)4]–. This suggests that A is [Fe(CO)5]– or [Fe(CO)4]– with a non-equilibrium structure. The form of the g-tensor components of both these 3d9 complexes requires a 3dz21 assignment for the unpaired electron on iron. When [Fe(CO)5] enriched in 13CO was studied, no well defined splittings were detected in the strongly broadened features of species A and B, but estimates of hyperfine coupling from the enhanced widths could be made. No radical anions were detected in irradiated solutions of [Fe2(CO)9], but [Fe3(CO)12] gave clear features for the anion [Fe3(CO)12]–, together, probably, with weak features for [Fe3(CO)11]–. Irradiation of dilute solutions of [Fe(CO)5] in trichlorofluoromethane gave a species thought to be [Fe(CO)5]+, despite the fact that its e.s.r. spectrum differs considerably from that assigned to this cation in [Cr(CO)6].