Light-induced metastable states in nitrosyl–ruthenium complexes containing ethylenediamine and oxalate ion ligands

Abstract

The metastable state which is produced by irradiation with the green-blue region of light was studied by IR and other spectroscopic techniques for solid states of newly synthesized nitrosyl–ruthenium complexes; cis-[Ru(Hox)(en)₂NO]Cl₂·EtOH, trans-[Ru(Hox)(en)₂NO]Cl₂, cis-K[Ru(ox)₂(en)NO]·3H₂O, cis-[Ru(Hox)(ox)(en)NO], and cis-K[Ru(ox)₂(en)NO] [ox = (CO₂)₂²⁻]. Continued irradiation at 77 K results in development of a photostationary state in the same way as for sodium nitroprusside. The population of the metastable state molecule in the photostationary state of each sample depends on the irradiation wavelength and reaches a maximum at 441.6 nm which is the shortest wavelength in the present study. A broad absorption band with an absorbance maximum at ≈600 nm is observed for the metastable state of a trans-[Ru(Hox)(en)₂NO]Cl₂ single crystal. The short wavelength tail of the band is considered to be involved in the photostationary equilibrium under blue light radiation. The metastable state molecules decay to the ground state at temperatures considerably higher than the two metastable molecules (MS₁ and MS₂) of sodium nitroprusside. The decay temperature of trans-[Ru(Hox)(en)₂NO]Cl₂, which is defined as the temperature at which the rate constants of the thermal decay becomes 10⁻³ s⁻¹, is 277 K, which is the highest value reached among the metastable states of nitrosyl complexes reported so far. In the Raman spectra of trans-[Ru(Hox)(en)₂NO]Cl₂, the Ru-(NO) stretching vibrations are observed at 604 cm⁻¹ and 476 cm⁻¹ for the ground and metastable state molecules, respectively.