L-EDGE X-RAY-ABSORPTION AND X-RAY MAGNETIC CIRCULAR-DICHROISM OF OXYGEN-BRIDGED DINUCLEAR IRON COMPLEXES

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-ore 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 (FeFeIII)-Fe-II complexes such as [Fe-2(III,II)(salmp)(2)](-) and [Fe-2(III,II)(bpmp)(mu-O2CC2H5)2](2-) can be interpreted as the sum of distinct Fe(n) 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 [Fe2(III,II)(bpmp)(mu-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, [Fe-2(Me(3)tacn)(2)-(mu-OH)(3)](BPh(4))(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.