Dedicated to Prof. José A. Olabe on the occasion of his 80th birthdayThe preparation and characterization of a new ruthenium nitrosyl based on the pentadentate ligand (CH 2 py) 2 Me[9]aneN 3 (1-methyl-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane) is reported. The octahedral species contains a {RuNO} 6 fragment and can be isolated in the solid state as a PF 6 À salt. In acetonitrile, this platform allows exploring the reduction processes in 1-electron steps from {RuNO} 6 to {RuNO} 8 , with associated E°values of 0.421 V and À 0.628 V (vs. Ag/AgCl, 3 M NaCl), respectively. The {RuNO} 7 species is paramagnetic, its EPR spectrum in vitrified acetonitrile at 90 K is consistent with an S = 1 = 2 center with g = (2.0095, 1.9992, 1.8785) coupled to a 14 N nucleus, with A = (6.9, 30.24, 1.85) × 10 À 4 cm À 1 . In acidified aqueous solution, the first reduction process at 0.101 V leads to the formation of {RuNO} 7 , as in aprotic medium (acetonitrile). However, the incorporation of a second electron is coupled to a protonation process of the nitroxyl group, generating a coordinated azanone (HNO) compound with pK a (HNO) = 11.0. Spectroscopic information obtained via spectroelectrochemistry and electronic structure calculations assist in the rationalization of results. Overall, this new compound enhances the library of nitrosylated Ru species with combined redox, acid-base, and spectroscopic characterization in water and confirms experimental correlations found in related species.