The reaction of cis-Ru(acac)(2)(CH3CN)(2) (acac = acetylacetonate) with 2,2'-dipyridylamine (L) in ethanolic medium resulted in facile one-pot synthesis of stable [(acac)(2)Ru-III(L)]ClO4 ([1]ClO4), trans-[(acac)(2)Ru-II(L)2] (2), trans[(acac)(2)Ru-III(L)(2)[ClO4 ([2]ClO4), and cis-[(acac)(2)Ru-II(L)(2)] (3). The bivalent congener 1 was generated via electrochemical reduction Of [1]ClO4. Although in [1](+) the dipyridylamine ligand (L) is bonded to the metal ion in usual bidentate fashion, in 2/[2](+) and 3, the unusual monodentate binding mode of L has been preferentially stabilized. Moreover, in 2/[2](+) and 3, two such monodentate L's have been oriented in the trans- and cis-configurations, respectively. The binding mode of L and the isomeric geometries of the complexes were established by their single-crystal X-ray structures. The redox stability of the Ru(II) state follows the order 1 < 2 much less than 3. In contrast to the magnetic moment obtained for [1]ClO4, mu = 1.84 mu(B) at 298 K, typical for low-spin Ru(III) species, the compound [2]ClO4 exhibited an anomalous magnetic moment of 2.71 mu(B) at 300 K in the solid state. The variable-temperature magnetic measurements showed a pronounced decrease of the magnetic moment with the temperature, and that dropped to 1.59 mu(B) at 3 K. The experimental data can be fitted satisfactorily using eq 2 that considered nonquenched spin-orbit coupling and Weiss constant in addition to the temperature-independent paramagnetism. [1]ClO4 and [2]ClO4 displayed rhombic and axial EPR spectra, respectively, in both the solid and the solution states at 77 K.