Nitrosyl complexes with {Ru-NO}6 and {Ru-NO}7 configurations have been isolated in the framework of [Ru(trpy)(L)(NO)] n+ [trpy = 2,2′:6′,2″-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline] as the perchlorate salts [4](ClO 4)3 and [4](ClO4)2, respectively. Single crystals of protonated material [4-H+](ClO4) 4·2H2O reveal a Ru-N-O bond angle of 176.1(7)° and triply bonded N-O with a 1.127(9) Å bond length. Structures were also determined for precursor compounds of [4]3+ in the form of [Ru(trpy)(L)(Cl)](ClO4)·4.5H2O and [Ru(trpy)-(L-H)(CH3CN)](ClO4)3·H 2O. In agreement with largely NO centered reduction, a sizable shift in ν(NO) frequency was observed on moving from [4]3+ (1953 cm -1) to [4]2+ (1654 cm-1). The Ru II-NO• in isolated or electrogenerated [4] 2+ exhibits an EPR spectrum with g1 = 2.020, g2 = 1.995, and g3 = 1.884 in CH3CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); 14N (NO) hyperfine splitting (A2 = 30 G) was also observed. The plot of ν(NO) versus E°({RuNO}6 → {RuNO}7) for 12 analogous complexes [Ru(trpy)(L′)(NO)] n+ exhibits a linear trend. The electrophilic Ru-NO+ species [4]3+ is transformed to the corresponding Ru-NO 2- system in the presence of OH- with k = 2.02 × 10-4 s-1 at 303 K. In the presence of a steady flow of dioxygen gas, the RuII-NO• state in [4] 2+ oxidizes to [4]3+ through an associatively activated pathway {ΔS‡ = -190.4 J K-1 M-1) with a rate constant (k[s-1]) of 5.33 × 10-3. On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)]2+ ([4]2+) undergoes facile photorelease of NO (kNO = 2.0 × 10-1 min-1 and t 1/2 ≈ 3.5 min) with the concomitant formation of the solvate [RuII(trpy)(L)(CH3CN)]2+ [2′] 2+. The photoreleased NO can be trapped as an Mb-NO adduct. © 2008 American Chemical Society.}, keywords={imidazole derivative; metal; nitrogen oxide; phenanthroline derivative; pyridine derivative; ruthenium, article; chemical structure; chemistry; conformation; spectrophotometry, Imidazoles; Metals; Models, Molecular; Molecular Conformation; Nitrogen Oxides; Phenanthrolines; Pyridines; Ruthenium; Spectrophotometry}, correspondence_address1={Kaim, W.; Institut für Anorganische Chemie, Pfaffenwaldring 55, D-70550 Stuttgart, Germany; email: kaim@iac.uni-stuttgart.de}, issn={00201669}, coden={INOCA}, pubmed_id={18311917}, language={English}, abbrev_source_title={Inorg. Chem.}, document_type={Article}, source={Scopus},