The novel ligand 4,4′-dicyanamidobiphenyl dianion (bp 2− ) has been synthesized and characterized by 13 C NMR spectroscopy, cyclic voltammetry, and crystallography. The crystal structure of [Ph 4 As] 2 [bp]•H 2 O showed that bp 2− is approximately planar with a dihedral angle of 8.2° between phenyl ring planes and the cyanamide groups in an anti conformation. The water of crystallization is asymmetrically hydrogen bonded between cyanamide groups of adjacent bp 2− ions. The crystal data for C 62 H 48 N 4 As 2 + H 2 O are monoclinic crystal system and space group P2 1 /c with a = 12.998(5) Å, b = 13.465(4) Å, c = 28.703(13) Å, β = 98.94(3)°, V = 4963(3) Å 3 and Z = 4. The structure was refined by using 4555 reflections with I > 2.5σ(I) to an R factor of 0.058. The complex, [{(NH 3 ) 5 Ru) 2 (μ-bp)][X] 4 , where X = tosylate or PF 6 − ions, was also synthesized and characterized by 1 H NMR spectroscopy, cyclic voltammetry, spectroelectrochemistry, and temperature-dependent magnetic susceptibility measurements. From cyclic voltammetry measurements, the comproportionation constants to form the mixed-valence complex [{(NH 3 ) 5 Ru) 2 (μ-bp)] 3+ were estimated to be 4.1, 16, and 22 in water, acetonitrile, and nitromethane, respectively. The trend and magnitude of K c suggests solvent valence trapping of a weakly coupled Class II ion. The MMCT band of the mixed-valence complex had to be deconvoluted from the low-energy LMCT band and had the following properties in acetonitrile, ν max = 8400 cm −1 , ε max = 3300 M −1 cm −1 , and Δν 1/2 = 3300 cm −1 . The weak superexchange mediating properties of bp 2− compared to 1,4-dicyanamidobenzene dianion were suggested to arise from the larger barrier to the formation of the radical anion bp − . Key words: cyanamido, mixed valence, superexchange, ruthenium.