X-ray crystallography identifies the aromatic donor group D = 2,5-dimethoxy-4-methylphenyl to be a suitable redox center for the construction of organic mixed-valence crystals owing to its large structural change attendant upon I e oxidation to the cation-radical (D.+). The combination of cyclic voltammetry, dynamic ESR line broadening, and electronic (NIR) spectroscopy allows the intervalence electron transfer between the redox centers in the mixed-valence system D-br-D.+ [where br can be an aliphatic trimethylene or an aromatic (poly)phenylene bridge] to be probed quantitatively. Independent measures of the electronic coupling matrix element (H) for D/D.+ electron exchange via Mulliken-Hush theory accord with the X-ray crystallographic data-both sufficient to consistently identify the various D-br-D-.+ according to the Robin-Day classification. Thus, the directly coupled biaryl D-D.+ is a completely delocalized cation in class III with the charge distributed equally over both redox centers. The trimethylene-and biphenylene-bridged cations D(CH2)(3)D.+ and D(ph)(2)D.+ with highly localized charge distributions are prototypical class II systems involving moderately coupled redox centers with H approximate to 400 cm(-1). The borderline region between class II/III is occupied by the phenylene-bridged cation D(ph)D.+ and the X-ray, CV, and NIR analyses yield ambivalent H values (which we believe to be) largely a result of an unusually asymmetric (20/80) charge distribution that is polarized between the D/D.+ redox centers.