L-Edge X-ray Absorption and X-ray Magnetic Circular Dichroism of Oxygen-Bridged Dinuclear Iron Complexes

G. Peng, S. P. Cramer, J. van Elp, S. P. Cramer, H. Jang, L. Que, W. H. Armstrong

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Iron L-edge X-ray absorption and X-ray magnetic circular dichroism (XMCD) spectroscopy have been used to study the electronic structure of dinuclear iron-oxo complexes with different types of magnetic and electronic interactions between the iron sites. Trapped-valence systems exhibit L-edges with clear multiplet structure. The L-edges of trapped-valence FeIIFeIII complexes such as [FeIII, II2 (salmp)2]- and [Fe2III, II (bpmp) (μ-O2CC2H5)2]2-can be interpreted as the sum of distinct Fe (II) and Fe (III) component spectra. Furthermore, an atomic multiplet theory including adjustable ligand field splittings can successfully simulate the Fe (II) and Fe (III) X-ray absorption. Reasonable ligand field parameters are obtained by optimizing the correspondence between calculated and experimental spectra. The XMCD for the [Fe2III, II (bpmp) (μ-O2CC2H5)2]2- complex is also reported; it exhibits an interesting magnetic field dependence that reflects the weak magnetic coupling between Fe (II) and Fe (III) ions. In contrast with the trapped-valence complex spectra, the L-edge spectrum for the electronically delocalized complex, [Fe2 (Me3tacn)2- (μ-OH)3] (BPh4)2·2MeOH, exhibits a broad L-edge spectrum with poorly resolved multiplet structure. L-edge spectroscopy is capable of characterizing electron delocalization on a very fast (femtosecond) time scale, while XMCD is an alternative technique for characterizing exchange interactions.

Original languageEnglish (US)
Pages (from-to)2515-2519
Number of pages5
JournalJournal of the American Chemical Society
Issue number9
StatePublished - 1995


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