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-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 Fe[sup II]Fe[sup III] complexes such as [Fe[sup III,II]2(salmp)[sub 2]][sup [minus]] and [Fe[sub 2][sup III,II](bpmp)([mu]-O[sub 2]CC[sub 2]H[sub 5])[sub 2]][sup 2[center dot]] 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 [Fe[sub 2][sup III,II](bpmp)([mu]-O[sub 2]CC[sub 2]H[sub 5])[sub 2]][sup 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[sub 2](Me[sub 3]tacn)[sub 2]-([mu]-OH)[sub 3]](BPh[sub 4])[sub 2]-2MeOH, exhibits a broad L-edge spectrum with poorly resolved multiplet structure. 35 refs., 4 figs.