A series of cobalt complexes of ligands based on the 2-(arylazo)pyridine architecture have been synthesized, and the precise structure and stoichiometry of the complexes depend critically on the identity of substituents in the 2, 4, and 6 positions of the phenyl ring. The 2-(arylazo)pyridine motif can support either Co-II complexes with neutral ligands, (CoCl2)-Cl-II(L-a)(2) (1), (CoCl2)-Cl-II(L-c)(2) (3), [(CoCl)-Cl-II(L-b)(2)](2) (PF6)(2) (5[PF6](2)), or Co-III complexes of reduced 2-(arylazo)pyridine ligand radical anions, L center dot-, (CoCl)-Cl-III(Lb center dot-)(2) (2), (CoCl)-Cl-III(Lc center dot-)(2) (4), and (CoMe)-Me-III(Lb center dot-)2 (6). All three members of the latter class are based on approximately trigonal-bipyramidal CoX-(L center dot-)(2) architectures [L = 2-(arylazo)pyridine] with two azo nitrogen atoms and the X ligand (X = Cl or Me) in the equatorial plane and two pyridine nitrogen atoms occupying axial positions. Density functional theory suggests that the electronic structure of the Co-III complexes is also dependent on the identity of X: the strong sigma-donor methyl gives a low-spin (S = 0) configuration, while the sigma/pi-donor chloro gives an intermediate-spin (S = 1) local configuration. In certain cases, one-electron reduction of the (CoX2L2)-X-II complex leads to the formation of (CoX)-X-III(L center dot-)(2); i.e., reduction of one ligand induces a further one-electron oxidation of the metal center with concomitant reduction of the second ligand.