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 (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)](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.

The bis(pentaammineruthenium(II)) complex of dicyanonorbornadiene has been prepared and characterized. Its photochemical conversion into a dicyanoquadricyclane complex by irradiation in methanol has been followed by UV−visible spectroscopy, IR spectroscopy, 1H NMR spectroscopy, and cyclic voltammetry. The dicyanonorbornadiene complex exhibits an intervalence transition in the 1000−1600 nm range when oxidized to the ruthenium(II)−ruthenium(III) state. This allows the determination of the effective coupling V ab through the dicyanonorbornadiene ligand, which is found as 0.023 eV. No such band is observed in the case of the dicyanoquadricyclane complex. These results show the possibility to modulate an intramolecular electron transfer process by using a photoisomerizable bridging ligand.