Identification of a Two-Coordinate Iron(I)-Oxalate Complex

Abstract

Exotic oxidation states of the first-row transition metals have recently attracted much interest. In order to investigate the oxidation states of a series of iron-oxalate complexes, an aqueous solution of iron(III) nitrate and oxalic acid was studied by infrared free liquid matrix-assisted laser desorption/ionization as well as ionspray mass spectrometry. Here, we show that iron is not only detected in its common oxidation states +II and +III, but also in its unusual oxidation state +I, detectable in both positive-ion and in negative-ion modes, respectively. Vibrational spectra of the gas phase anionic iron oxalate complexes [Fe^III (C₂ O₄ )₂ ]^- , [Fe^II (C₂ O₄ )CO₂ ]^- , and [Fe^I (C₂ O₄ )]^- were measured by means of infrared photodissociation spectroscopy and their structures were assigned by comparison to anharmonic vibrational spectra based on second-order perturbation theory.

Keywords: IR-FL-MALDI; IRPD Spectroscopy; Iron Complexation; Iron(I); Unusual Oxidation State.