AbstractThe Ru complex [Ru^II(bda‐κ‐N²O²)(N‐NH₂)₂] (1; bda²⁻=2,2′‐bipyridine‐6,6′‐dicarboxylate, N‐NH₂=4‐(pyridin‐4‐yl)aniline) was used as a synthetic intermediate to prepare new Ru^II and Ru^III bda complexes that contain NO⁺, MeCN, or H₂O ligands. In acidic solution complex 1 reacts with an excess of NO⁺ (generated in situ from sodium nitrite) to form a new Ru complex in which the aryl amine ligand N−NH₂ is transformed into a diazonium salt [N‐N₂⁺=4‐(pyridin‐4‐yl)benzenediazonium)] together with the formation of a new Ru(NO) moiety in the equatorial zone, to generate [Ru^II(bda‐κ‐N²O)(NO)(N‐N₂)₂]³⁺ (2³⁺). Here the bda²⁻ ligand binds in a κ‐N²O tridentate manner with a dangling carboxylate group. Similarly, complex 1 can also react with a coordinating solvent, such as MeCN, at room temperature to give [Ru^II(bda‐κ‐N²O)(MeCN)(N‐NH₂)₂] (3). In acidic aqueous solutions, a related reaction occurs in which solvent water coordinates to the Ru center to form {[Ru^II{bda‐κ‐(NO)³}(H₂O)(N‐NH₃)₂](H₂O)_n}²⁺ (4²⁺) and is strongly hydrogen‐bonded with additional water molecules in the second coordination sphere. Furthermore, under acidic conditions the aniline ligands are also protonated to form the corresponding anilinium cationic ligands N‐NH₃⁺. Additionally, the one‐electron oxidized complex {[Ru^III{bda‐κ‐(NO)^3.5}(H₂O)(N‐NH₃)₂](H₂O)_n}³⁺ (5³⁺) was characterized, in which the fractional value in the κ notation indicates the presence of an additional contact to the pseudo‐octahedral geometry of the Ru center. The coordination modes of the complexes were studied in the solid state and in solution through single‐crystal XRD, X‐ray absorption spectroscopy, variable‐temperature NMR spectroscopy, and DFT calculations. While κ‐N²O is the main coordination mode for 2³⁺ and 3, an equilibrium that involves isomers with κ‐N²O and κ‐NO² coordination modes and neighboring hydrogen‐bonded water molecules is observed for 4²⁺ and 5³⁺.