The impact of counterion on the metastable state properties of nitrosyl ruthenium complexes

International audience; In the present study four new complexes of the trans-[RuNO(NH 3) 4 F] 2+ cation with noble-metal anions [PtCl 6 ] 2-, [PdCl 4 ] 2-and [PtCl 4 ] 2-, and perchlorate anion ClO 4-were synthesized and characterized by spectroscopic (IR, UV/vis), calorimetric (DSC) and single crystal X-Ray diffraction methods. All three complexes with the platinum and palladium cations crystallize in a non-centrosymmetric structure, which is determined by N-H•••Halogen intermolecular interactions. The irradiation of the complexes by light in the spectral range of 300-420 nm induces Ru-ON isomers MS1, and the subsequent irradiation of MS1 in trans-[RuNO(NH 3) 4 F](ClO 4) 2 by 940 nm light results in Ru-(η 2-(NO) isomer MS2 formation, which were detected by IR and UV/vis-spectroscopy. For trans-[RuNO(NH 3) 4 F](ClO 4) 2 and trans-[RuNO(NH 3) 4 F][PdCl 4 ] the activation energy (E a) and frequency factors (lgk 0) of the MS1→GS transformation were determined, which are 104(1) kJ mol-1 and 15.0(2), and 112(6) kJ mol-1 and 16.0(9), respectively. It is shown, that in these complexes the MS1 isomers exhibit excellent thermal stability, trans-[RuNO(NH 3) 4 F][PdCl 4 ] exhibits the highest thermal stability known up to now. The spectroscopic analysis of ground and metastable states allows to underline two important features: i) the absorption of a counterion in the excitation range results in a decreased efficiency of light absorption of the nitrosyl complex cation and consequently leads to a decrease in metastable state population; ii) the interactions with the counterion can influence the position of absorption bands of MS1 and MS2, which requires to change the excitation wavelength for the achievement of the maximum metastable state population. Obtained results can be expanded and applied for other metastable systems, like complexes containing nitrite (NO 2-) or sulfoxide-like (SO) ligands.