Abstract
The photochemical behavior of a series of trans-[Ru(NH 3) 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 (d π → NO) charge transfer (MLCT) transitions. Irradiation of aqueous solutions of these complexes with near-UV light (300–370 nm) labilizes NO, i.e., trans -[ Ru( NH 3) 4 L( NO)] 3+ → hν [ Ru( NH 3) 4 L( H 2 O)] 3++ NO Quantum yields for [Ru(NH 3) 4L(H 2O)] 3+ formation ( φ Ru(III)) are sensitive to the natures of L, λ irr and pH. The lowest quantum yields ( λ irr=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 d π → NO MLCT state in these systems.
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