Two new complexestrans-(H O)[RuNO(NH ) F](NO ) F ·0.5H O (I) andtrans-[RuNO(NH ) F](ClO )Cl (II) are synthesized and characterized by single crystal X-ray diffraction. The complexes crystallized in the centrosymmetric space groupsI4/mandP2 /ndue to specific intermolecular interactions; the strongest ones are represented by N-H-O contacts. The irradiation of the complexes in the blue-light range induces the formation of Ru-ON isomers (MS1), determined by IR spectroscopy and differential scanning calorimetry (DSC). The subsequent excitation of MS1 by infrared light induces the formation of Ru-(η -(NO)) (MS2) isomers, confirmed by the same techniques. Using combined IR and DSC analysis, the activation barriers (E ) and frequency factors (lg k ) of the MS1 → GS and MS2 → GS reactions are determined. According to the kinetic parameters, the calculated lifetimes (k ) of MS1 at 300 K are 33 and 178 min forIandII, respectively. To the best of our knowledge, the thermal stability of MS1 inIIis the highest among known related complexes. The thermal stability of MS2 was found to be lower (the lifetimes are 0.12 and 0.02 s at 300 K forIandII, respectively), which is characteristic of these states. The high thermal stability of MS1 can be applied for the design of photochromic materials and to generally facilitate the investigation of the states. 3 3 4 3 1.5 1.5 2 3 4 4 1 a 0 2 −1