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 Os{double bond, long}O 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 p_z(O) (L = oxalate or malonate) → π^*(Os{double bond, long}O) + π^*(C{double bond, long}O), and the composition of p_z(O) participate in the transition for monooxo-osmium (VI) complexes. The lowest energy absorptions of the complexes were mainly attribute to Os(d_xy) + π(L) → π^*(Os{double bond, long}O). The calculated phosphorescence emissions of the complexes were originated from ³[(π^*(Os{double bond, long}O) + π^*(L))¹((d_xy(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.