Site-Selective XANES and EXAFS: A Demonstration with Manganese Mixtures and Mixed-Valence Complexes

This paper presents the first demonstration that chemical shifts in X-ray fluorescence energies can be used to obtain site-selective X-ray absorption spectra. X-ray absorption spectroscopy (XAS) has become a powerful tool for probing both geometric and electronic structure. Here site-selective XANES and EXAFS using high-resolution fluorescence detection are demonstrated for a physical mixture of MnF{sub 2} and BaMn{sub 8}O{sub 16}{center_dot}2H{sub 2}O and for a Mn{sup II}Mn{sup III}{sub 2} mixed-valence complex, Mn{sub 3}O(O{sub 2}CPh){sub 6}(py){sub 2}(H{sub 2}O). There are many cases where fluorescence lines change with chemical environment; hence this method of site-selective XAS should have broad applicability. The main obstacle at the moment is signal-to-noise, but with new high-brightness synchrotron radiation sources and a larger collection solid angle, site-selective XAS using high-resolution fluorescence detection should become a more common and valuable technique. 24 refs., 2 figs.