Spin-Orbit Interactions in Osmium Complexes

Osmium compounds with the Os 5d 4 electron configuration and an octahedral environment of neighboring atoms attract much attention due to the influence of the spin-orbit interaction on the appearance of magnetic properties in materials. X-ray absorption near edge structure (XANES) spectroscopy makes it possible to obtain information about the value of the spin–orbit interaction from measuring the intensity ratio of lines near the absorption edges. The influence of the spin–orbit interaction on the Os L2,3-edge XANES spectra of osmium compounds having an octahedral environment of halogen atoms is studied. Two types of systems are investigated, namely, isolated osmium clusters in complex compounds and the OsCl4 compound containing Os polymer chains bridged by Cl atoms. Magnetic-susceptibility measurements show a nonmagnetic ground state and Van Vleck paramagnetism in the case of isolated clusters and a nonzero magnetic moment over the entire temperature range in OsCl4. As a result of measurements of the XANES spectra, high values of the line intensity ratio are obtained near the Os L3/L2 absorption edges, which is associated with the strong effect of the spin-orbit interaction on the electronic structure. The theoretical analysis of the XANES spectra of Os compounds with different ligands and outer-sphere cations shows that the electronic structure and magnetic properties depend on the spin–orbit interaction, the crystal-field splitting, the electron-pairing energy, and noncubic distortions of the Os environment.