Electronic structure and soft-X-ray-induced photoreduction studies of iron-based magnetic polyoxometalates of type \(M)M-5\(12)Fe-30(III) (M = Mo-VI, W-VI)
Résumé
Giant Keplerate-type molecules with a \Mo72Fe30\ core show a number of very interesting properties, making them particularly promising for various applications. So far, only limited data on the electronic structure of these molecules from X-ray spectra and electronic structure calculations have been available. Here we present a combined electronic and magnetic structure study of three Keplerate-type nanospheres-two with a \Mo72Fe30\ core and one with a \W72Fe30\ core by means of X-ray absorption spectroscopy, X-ray magnetic circular dichroism (XMCD), SQUID magnetometry, and complementary theoretical approaches. Furthermore, we present detailed studies of the Fe3+-to-Fe2+ photoreduction process, which is induced under soft X-ray radiation in these molecules. We observe that the photoreduction rate greatly depends on the ligand structure surrounding the Fe ions, with negatively charged ligands leading to a dramatically reduced photoreduction rate. This opens the possibility of tailoring such polyoxometalates by X-ray spectroscopic studies and also for potential applications in the field of X-ray induced photochemistry.