CARATTERIZZAZIONE DI COMPLESSI DI OSMIO TRAMITE SPETTROSCOPIE XAS/XES: ESPERIMENTI E TEORIA

For the first time RIXS maps and high resolution XANES spectra were measured for OsCl3, [Os(bpy)2(CO)Cl]+, Os3(CO)12 and [(η6-biphenyl)Os(bpy)I]+. Experiment was performed on the ID26 beamline at ESRF. The chosen method allows obtaining much more informative spectra compared to the standard TFY spectra and therefore the data published in literature concerning some of the studied samples. Analysis of RIXS maps suggests that multiplet effects are relatively weak in these systems, which justifies the use of monoelectronic approximation for the modeling of XANES spectra for these compounds. Geometry optimization of the studied complexes was performed within the DFT framework by ADF 2010 code. Obtained structural parameters showed good agreement with diffraction data, available for some samples. Optimization with different exchange-correlation potentials yielded similar results, which confirms the reliability of the method. Modeling of both TFY and HERFD XANES spectra was performed using two different approaches. The first one was based on molecular orbitals, calculated by ADF as a result of relativistic single-point calculation. Orbitals of interest were projected on the grid around the absorbing osmium atom and consequently corresponding transition matrix elements were calculated using ADFemis software. The second code used for XANES simulations was FDMNES 2010. It employs finite difference method to solve Schrödinger's equation and unlike many other XANES codes allows performing calculations beyond the muffin-tin approximation for a potential. Both methods gave similar results yielding in the good agreement with the experiment. However, the use of ADF/ADFemis tandem seems more preferable for the studied compounds, because the calculations take significantly less time, electron density distribution is calculated self-consistently and there is no uncertainty for the choice of the starting point for the spectrum (i.e. LUMO position, which is analogous to the Fermi level in FDMNES). Also it is very important that ADF is a versatile tool to study the electronic structure of matter and therefore many chemical and physical properties of the system can be calculated within it. In that case good agreement for the XANES spectrum justifies the quality of the calculated electronic structure of the complex and therefore proves the reliability of other relevant properties of the system, calculated using this package.