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 Ru2+, Os2+, and Pt2+; the bridging ligands are 2,3- and 2,5-dpp (dpp = bis(2-pyridyl)pyrazine), and the terminal ligands an Cl- and bpy (bpy = 2,2'-bipyridine). [Os(bpy)(2)(mu -2,3-dpp)Ru{mu -2,3-dpp)PtCl2}2] (OsRuPt2) and [Os(mu -2,3-dpp)Ru-[mu -2,3-dpp)PtCl2](2)}(3)](PF6)(8) (OsRu3Pt6), 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. OsRuPt2 and OsRu3Pt6 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 Os2+ and the bridging ligand mu -2,3-dpp and that all the absorbed energy is efficiently channeled to the single Os-based unit. OsRu3Pt6 appears to be the first decanuclear species displaying such efficient antenna effect.