ELECTRONIC STRUCTURE IN THE INTERVALENCE TRANSFER ABSORPTION BAND OF A MIXED-VALENCE DIMER.

Article abstract of DOI:10.1021/ja00351a031

Electronic structure has been observed in the intervalence transfer (IT) absorption band of the weakly coupled mixed-valence dimer left bracket (bpy)//2ClO s**I** I(PPh//2Ph//2P)O//s**I**I**ICl(bpy)//2 right bracket **3** plus (bpy is 2,2 prime -bipyridine). The origin of the structure lies in the large spin-orbit (SO) coupling constant ( lambda //O//s) for osmium which leads to well separated SO states for the Os**I**I**I d pi **5 electronic configuration. For Os**I**I**I-bpy monomers, low-energy d pi transitions between the SO states are observed in the near-infrared (near-IR). Optical electron transfer in the mixed-valence dimer results in the formation of a 'new' Os(III) site in one of three possible SO states (1E prime . 2E prime , or 3E prime ), and hence the IT manifold should contain three components separated by the energy differences between the SO states at the Os(III) site. In addition to the expected d pi -d pi absorption bands, the spectrum of the Os(II)-Os(III) dimer in the near-IR shows two broad, solvent-dependent bands which are assignable to IT transitions. The bands are separated in energy by approximately the energy difference between the two lowest SO states as expected.