Solvation and Speciation of Cobalt(II). A Theoretical X-Ray Absorption and RIXS Study

Abstract The X-ray spectroscopic signatures of solvated Co2+ ions mimicking the aqueous solution of CoCl2 are investigated accounting for multiconfigurational as well as spin-orbit coupling effects. To this end the RASSCF/RASSI methodology with second order corrections due to dynamical correlation (RASPT2) is employed. Emphasis is put on the identification of spectral signatures of different species in octahedral, [Co(H2O)6-xClx](2-x)+, and tetrahedral, [Co(H2O)4-xClx](2-x)+, coordination. X-ray absorption spectra show distinct differences in the L3 band only. Here, the best agreement between theory and experiment is obtained for the hexaaqua complex [Co(H2O)6]2+. For better identification of particular species it is proposed to use RIXS spectroscopy, which shows pronounced species-dependent inelastic features.