Tetranuclear Tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-j]phenazineruthenium Complex: Synthesis, Wide-Angle X-ray Scattering, and Photophysical Studies.

The tetranuclear ruthenium complex {Ru(tpphz)Ru(bpy)(2)}(8+), where tpphz is tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-j]phenazine, has been synthesized by reaction of Ru(tpphz)(3) with [Ru(bpy)(2)Cl(2)] and by reaction of Ru(bpy)(2)(tpphz) with [Ru(DMSO)(4)Cl(2)]. The large distance between the chiral centers allows full (1)H NMR interpretation despite the mixture of eight stereoisomers. The tetranuclear complex was further characterized by electrospray mass spectrometry and by the wide-angle X-ray scattering technique, which confirmed the starburst geometry. The photophysical properties of the tetranuclear complex in acetonitrile were studied and compared with those of Ru(tpphz)(3) (1 x 10(-)(4) M acidic solution) and (bpy)(2)Ru(tpphz)Ru(bpy)(2) model molecules. The tetranuclear complex gives rise to a single emission, attributed to metal-to-ligand charge-transfer states involving peripheral Ru centers and tpphz bridging ligands.