Quantum chemistry study on electron structures and spectroscopic properties of monooxo- and dioxo-osmium (VI) complexes with ring ligands

The electronic geometries and spectroscopic properties of trans-dioxo- and monooxo-osmium (VI) complexes have been investigated theoretically. The geometry structures of the complexes were fully optimized using the B3LYP/LANL2DZ method for the ground state and the CIS/LANL2DZ method for the excited state. The calculated geometry parameters agree well with the available experimental data in the ground state. The bond length of OsO bond is lengthened in excited state relative to that of the ground state for trans-dioxo-osmium (VI) complexes, but shorten for monooxo-osmium (VI) complexes. Among the calculated dipole-allowed absorptions at λ > 240 nm, the intense absorptions of the complexes were mainly attributed to pz(O) (L = oxalate or malonate) → π∗(OsO) + π∗(CO), and the composition of pz(O) participate in the transition for monooxo-osmium (VI) complexes. The lowest energy absorptions of the complexes were mainly attribute to Os(dxy) + π(L) → π∗(OsO). The calculated phosphorescence emissions of the complexes were originated from 3[(π∗(OsO) + π∗(L))1((dxy(Os) + π∗(L))1] excited state. The calculation revealed that the emissions of the monooxo-osmium complexes are blue-shift compared with dioxo-osmium complexes when the ligands are same, and the lowest excited energy is higher when the ring is larger (i.e., the electron-donating groups are added) for these two kinds of the complexes.