Polynuclear polypyridine complexes incorporating Ru(II), Os(II), and Pt(II): decanuclear dendrimeric antennas.
The "complexes as metal/complexes as ligand" strategy has been used to prepare new polynuclear heterometallic complexes containing two, 3, 4, and ten metal units. The metal ions employed are Ru(2+), Os(2+), and Pt(2+); the bridging ligands are 2,3- and 2,5-dpp (dpp = bis(2-pyridyl)pyrazine), and the terminal ligands are Cl(-) and bpy (bpy = 2,2'-bipyridine). [Os(bpy)(2)(mu-2,3-dpp)Ru[(mu-2,3-dpp)PtCl(2)](2)](PF(6))(4) (OsRuPt(2)) and [Os[(mu-2,3-dpp)Ru[(mu-2,3-dpp)PtCl(2)](2)](3)](PF(6))(8) (OsRu(3)Pt(6)), which have a dendritic structure, are the first examples of polynuclear complexes based on the dpp bridging ligand simultaneously containing three different metals. All of the new compounds feature absorption spectra with intense ligand-centered transitions in the UV region and metal-to-ligand charge transfer (MLCT) bands in the visible region. The complexes are luminescent both at room temperature in acetonitrile solution and at 77 K in butyronitrile rigid matrix. OsRuPt(2) and OsRu(3)Pt(6) luminesce in the near-infrared spectral region at 975 and 875 nm, respectively, at room temperature. This indicates that the emitting state is a (formally triplet) MLCT involving Os(2+) and the bridging ligand mu-2,3-dpp and that all the absorbed energy is efficiently channeled to the single Os-based unit. OsRu(3)Pt(6) appears to be the first decanuclear species displaying such efficient antenna effect.