Relativistic electronic structure of staggered and eclipsed conformations of octachlorodiosmate(III)

Symmetry-adapted angular momentum basis functions have been generated for the D_4d* and D_4h* molecular double point groups. These basis functions are used to obtain the relativistic molecular orbitals for the staggered (D_4d) and eclipsed (D_4h) rotameric geometries of octachlorodiosmate(III) via the self-consistent field Dirac Scattered-Wave (SCF-DSW) method. Double-point-group symmetry arguments and relativistic molecular orbital calculations for the Os₂Cl₈ ^2- ions indicate that the molecular orbitals involving the σ, iπ, δ, and δ* metal-metal bond components remain nondegenerate in both conformations. Spin-orbit interaction splits the π bond component of both conformers by about 0.35 eV and removes the orbital degeneracy involving the δ and δ* bond components of the staggered conformer. Double-point-group arguments and the results of DSW calculations on the staggered conformer allow us to reassign the two lowest absorption bands seen in the visible spectrum as being primarily metal-metal based.