Advanced X-ray spectroscopy experiments can contribute to elucidation of the mechanism of water oxidation in biological (tetra-manganese complex of Photosystem II) and artificial systems. Although the electronic structure of the catalytic metal site is of high interest, it is experimentally not easily accessible. Therefore, we and other researchers are working towards a comprehensive approach involving a combination of methods, namely (1) quantitative analysis of X-ray absorption near-edge structure (XANES) spectra collected at the K-edge and, in the long run, at the L-edge of manganese; (2) high-resolution X-ray emission spectroscopy (XES) of K alpha and K beta lines, (3) two-dimensional resonant inelastic X-ray scattering (RIXS) spectra. Collection of these spectroscopic data sets requires state-of-the-art synchrotron radiation facilities as well as experimental strategies to minimize the radiation-induced modifications of the samples. Data analysis requires the use and development of appropriate theoretical tools. Here, we present exemplary data collected for three multi-nuclear synthetic Mn complexes with the Mn ions in the oxidation states II, III, and IV, and for Mn-VII of the permanganate ion. Emission spectra are calculated for the Mn-VII ion using both multiple-scattering (MS) approach and time-dependent density functional theory (TDDFT).
