Photochemical reactions of trans-[Ru(NH3)4L(NO)]3+ complexes

The photochemical behavior of a series of trans-[Ru(NH3)4L(NO)]3+ complexes, where L=nitrogen bound imidazole, L-histidine, 4-picoline, pyridine, nicotinamide, pyrazine, 4-acetylpyridine, or triethylphosphite is reported. In addition to ligand localized absorption bands (<300 nm), the electronic spectra of these complexes are dominated by relatively low intensity bands assigned as ligand field (LF) and metal to ligand (dπ → NO) charge transfer (MLCT) transitions. Irradiation of aqueous solutions of these complexes with near-UV light (300–370 nm) labilizes NO, i.e., Quantum yields for [Ru(NH3)4L(H2O)]3+ formation (φRu(III)) are sensitive to the natures of L, λirr and pH. The lowest quantum yields (λirr=310 nm) were found for L = imidazole (0.03) and L-histidine (0.04), while much higher values were found for L=P(OEt)3 (0.30). Irradiation at longer wavelengths does not induce photochemical reactivity. These results are interpreted in terms of the expected reactivities of dπ → NO MLCT state in these systems.