Nitric Oxide Production by Visible Light Irradiation of Aqueous Solution of Nitrosyl Ruthenium Complexes

[RuIIL(NH3)4(pz)RuII(bpy)2(NO)](PF6)5 (L is NH3, py, or 4-acpy) was prepared with good yields in a straightforward way by mixing an equimolar ratio of cis-[Ru(NO2)(bpy)2(NO)](PF6)2, sodium azide (NaN3), and trans-[RuL(NH3)4(pz)] (PF6)2 in acetone. These binuclear compounds display ν(NO) at ca. 1945 cm-1, indicating that the nitrosyl group exhibits a sufficiently high degree of nitrosonium ion (NO+). The electronic spectrum of the [RuIIL(NH3)4(pz)RuII(bpy)2(NO)]5+ complex in aqueous solution displays the bands in the ultraviolet and visible regions typical of intraligand and metal-to-ligand charge transfers, respectively. Cyclic voltammograms of the binuclear complexes in acetonitrile give evidence of three one-electron redox processes consisting of one oxidation due to the Ru2+/3+ redox couple and two reductions concerning the nitrosyl ligand. Flash photolysis of the [RuIIL(NH3)4(pz)RuII(bpy)2(NO)]5+ complex is capable of releasing nitric oxide (NO) upon irradiation at 355 and 532 nm. NO production was detected and quantified by an amperometric technique with a selective electrode (NOmeter). The irradiation at 532 nm leads to NO release as a consequence of a photoinduced electron transfer. All species exhibit similar photochemical behavior, a feature that makes their study extremely important for their future application in the upgrade of photodynamic therapy in living organisms.