Paramagnetic diruthenium(III) complexes (acac)(2)Ru-III(mu-OC2H5)(2)Ru-III(acac)(2) (6) and [(acac)(2)Ru-III(mu-L)Ru-III(acac)(2)]-(ClO4)(2), [7](ClO4)(2), were obtained via the reaction of binucleating bridging ligand, N,N,N',N'-tetra(2-pyridyl)-1,4-phenylenediamine [(NC5H4)(2)-N-C6H4-N-(NC5H4)(2), L] with the monomeric metal precursor unit (acac)(2)Ru-II(CH3CN)(2) in ethanol under aerobic conditions. However, the reaction of L with the metal fragment Ru-II(bpy)(2)(EtOH)(2)(2+) resulted in the corresponding [(bpy)(2)Ru-II (mu-L) Ru-II(bpy)(2)](ClO4)(4), [8](ClO4)(4), Crystal structures of L and 6 show that, in each case, the asymmetric unit consists of two independent half-molecules. The Ru-Ru distances in the two crystallographically independent molecules (F and G) of 6 are found to be 2.6448(8) and 2.6515(8) Angstrom, respectively. Variable-temperature magnetic studies suggest that the ruthenium(III) centers in 6 and [7](ClO4)(2) are very weakly antiferromagnetically coupled, having J = -0.45 and -0.63 cm(-1), respectively. The g value calculated for 6 by using the van Vleck equation turned out to be only 1.11, whereas for [7](ClO4)(2), the g value is 2.4, as expected for paramagnetic Ru(III) complexes. The paramagnetic complexes 6 and [7](2+) exhibit rhombic EPR spectra at 77 K in CHCl3 (g(1) = 2.420, g(2) = 2.192, g(3) = 1.710 for 6 and g(1) = 2.385, g(2) = 2.177, g(3) = 1.753 for [7](2+)). This indicates that 6 must have an intermolecular magnetic interaction, in fact, an antiferromagnetic interaction, along at least one of the crystal axes. This conclusion was supported by ZINDO/1-level calculations. The complexes 6, [7](2+), and [8](4+) display closely spaced Ru(III)/Ru(II) couples with 70, 110, and 80 mV separations in potentials between the successive couples, respectively, implying weak intermetallic electrochemical coupling in their mixed-valent states. The electrochemical stability of the Ru(II) state follows the order: [7](2+) < 6 < [8](4+). The bipyridine derivative [8](4+) exhibits a strong luminescence [quantum yield (phi) = 0.18] at 600 nm in EtOH/MeOH (4:1) glass (at 77 K), with an estimated excited-state lifetime of approximately 10 mus.