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](CIO4)(3) and [4](CIO4)2, respectively. Single crystals of protonated material [4-H+](ClO4)(4)center dot 2H(2)O reveal a Ru-N-O bond angle of 176.1(7)degrees and triply bonded N-O with a 1.127(9) angstrom bond length. Structures were also determined for precursor compounds of [4](3+) in the form of [Ru(trpy)(Q(Cl)](ClO4)(-4).5H(2)O and [Ru(trpy)(L-H)(CH3CN)](CIO4)(3) Epsilon center dot H2O. In agreement with largely NO centered reduction, a sizable shift in nu(NO) frequency was observed on moving from [4](3+) (1953 cm(-1)) to [4](2+) (1654 cm(-1)). The Ru-II-NO center dot in isolated or electrogenerated [4](2+) exhibits an EPR spectrum with g(1) = 2.020, g(2) = 1.995, and g(3) = 1.884 in (CHCN)-C-3 at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); N-14 (NO) hyperfine splitting (A(2) = 30 G) was also observed. The plot of nu(NO) versus E degrees({Ru-NO}(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 system in the presence of OH- with k = 2.02 x 10(-4) S-1 at 303 K. In the presence of a steady flow of dioxygen gas, the Ru-II-NO center dot state in [4](2+) oxidizes to [4](3+) through an associatively activated pathway (Delta S-double dagger = -190.4 J K-1 M-1) with a rate constant (k[s(-1)]) of 5.33 x 10(-3). On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(Q(NO)](1+) ([4](2+)) undergoes facile photorelease of NO (k(No) = 2.0 x 10(-1) min(-1) and t1/2; z approximate to 3.5 min) with the concomitant formation of the solvate [Rul1(trpy)(L)(CH3CN)](2+) [2'](2+). The photoreleased NO can be trapped as an Mb-NO adduct.