A structurally diverse mixed-metal complex with mixed bridging ligands [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12: Modulating orbital energetics within a supramolecular architecture

A structurally diverse supramolecular complex, [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12, has been prepared (bpy = 2,2′-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, and dpq = 2,3-bis(2-pyridyl)quinoxaline). The supramolecular assembly contains four light absorbing osmium metal centers coupled to two ruthenium metal centers linked by two different bridging ligands (BL) capped by bpy terminal ligands. This supramolecule possesses a lowest unoccupied molecular orbital (LUMO) localized on the central μ-dpq bridging ligand (BL) and a highest occupied molecular orbital (HOMO) localized on the terminal Os centers, providing significant spatial separation of these donor and acceptor orbitals. This hexametallic complex absorbs throughout the visible region due to overlapping singlet metal-to-ligand charge transfer (MLCT) transitions from the Os and Ru chromophores to each π-acceptor ligand. The Os based 3MLCT bands extend into the near-infrared. The light absorbing and redox properties for this hexametallic complex have been elucidated using smaller model fragments and spectroelectrochemistry.