Complex Series [Ru(tpy)(dpk)(X)]ⁿ⁺ (tpy = 2,2‘:6‘,2‘ ‘-Terpyridine; dpk = 2,2‘-Dipyridyl Ketone; X = Cl^-, CH₃CN, NO₂^-, NO⁺, NO^•, NO^-):  Substitution and Electron Transfer, Structure, and Spectroscopy

The complex framework [Ru(tpy)(dpk)]²⁺ has been used to study the generation and reactivity of the nitrosyl complex [Ru(tpy)(dpk)(NO)]³⁺ ([4]³⁺). Stepwise conversion of the chloro complex [Ru(tpy)(dpk)(Cl)]⁺ ([1]⁺) via [Ru(tpy)(dpk)(CH₃CN)]²⁺ ([2]²⁺) and the nitro compound [Ru(tpy)(dpk)(NO₂)]⁺ ([3]⁺) yielded [4]³⁺; all four complexes were structurally characterized as perchlorates. Electrochemical oxidation and reduction was investigated as a function of the monodentate ligand as was the IR and UV−vis spectroscopic response (absorption/emission). The kinetics of the conversion [4]³⁺/[3]⁺ in aqueous environment were also studied. Two-step reduction of [4]³⁺ was monitored via EPR, UV−vis, and IR (ν(NO), ν(CO)) spectroelectrochemistry to confirm the {RuNO}⁷ configuration of [4]²⁺ and to exhibit a relatively intense band at 505 nm for [4]⁺, attributed to a ligand-to-ligand transition originating from bound NO^-.