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

Abstract

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.

Keywords: NEVPT2; absorption spectra; bpy phen; multireference; osmium complexes.