Ab initio multireference calculation of electronic spectra of the osmium complexes, [Os(bpy)   3 ]   2 + and [Os(phen)   3 ]   2 + .

The spin-orbit coupling corrected absorption spectra of osmium complexes, [Os(bpy)   3 ]   2 + and [Os(phen)   3 ]   2 + , were calculated by using ab initio multireference perturbation method (NEVPT2) with relativistic effects taken into account throughout ZORA approximation and corresponding all-electron basis sets. For the same purpose, the time-dependent DFT techniques were used. A very good agreement between NEVPT2 and experimental spectra should be highlighted, especially for the MLCT transitions that occur in visible and near-UV regions ( 16 , 000 - 33 , 000 cm   - 1 ). Moreover, the present study offers description of excited states of titled osmium complexes and their spectra interpretation using molecular orbitals.