Complexes of Osmium with the 2-[(Diphenylphosphanyl)-methyl]-pyridine Ligand

We report new osmium complexes based upon the 2-[(diphenylphosphanyl)-methyl]-pyridine ligand. Hexafluorophosphate salts of bis(3,4,7,8-tetramethyl-1,10-phenantholine)(2-[(diphenylphosphanyl)-methyl]-pyridine)osmium(II) (1), and bis(2-[(diphenylphosphanyl)-methyl]-pyridine)(4,7-diphenyl-1,10-phenantholine)osmium(II) (2) have been synthesized, and X-ray structures have been obtained. Indexing and unit cell refinement of both 1 and 2 indicated a monoclinic P lattice. The space groups were found to be P1̅ (No. 2) and P21/c, respectively. Both 1 and 2 were found to have the same emission at 645 nm despite the differences in structure. Through density functional theory (DFT) calculations we were able to conclude that the highest occupied molecular orbital (HOMO) of the complexes is the dxy orbital on the osmium, while the lowest unoccupied molecular orbital (LUMO) is the b1(Ψ)π* system of the phenanthroline. However, we found that dxy did not have the correct orientation to enable charge transfer to the phenanthroline, and the actual metal-to-ligand charge transfer (MLCT) transition is dxz (HOMO-1) to the π* LUMO of the phenanthroline.