Spectroscopic Characterization and Reactivity of Triplet and Quintet Iron(IV) Oxo Complexes in the Gas Phase

Abstract

Closely structurally related triplet and quintet iron(IV) oxo complexes with a tetradentate aminopyridine ligand were generated in the gas phase, spectroscopically characterized, and their reactivities in hydrogen-transfer and oxygen-transfer reactions were compared. The spin states were unambiguously assigned based on helium tagging infrared photodissociation (IRPD) spectra of the mass-selected iron complexes. It is shown that the stretching vibrations of the nitrate counterion can be used as a spectral marker of the central iron spin state. At full stretch: The stretching vibrations of the nitrate counterions of gaseous iron(IV) oxo complexes are used for spin-state assignment. It opens a route to compare hydrogen-atom- and oxygen-atom-transfer reactions of the isolated triplet- and quintet-state complexes under well-defined gas-phase conditions.