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)](3)}(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)](2+) with [Ru(bpy)(2)Cl-2] and by reaction of [Ru(bpy)(2)(tpphz)](2+) with [Ru(DMSO)(4)Cl-2]. The large distance between the chiral centers allows full H-1 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)](2+) (1 x 10(-4) M acidic solution) and [(bpy)(2)Ru(tpphz)Ru(bpy)(2)](4+) 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.