Intrazeolitic photoreactions of Ru (bpy)₃³⁺ with methyl viologen

Abstract

Encapsulation of Ru(bpy)₃³⁺ in zeolite Y supercages at low loadings leads to a slow reaction (days) with water with eventual recovery of Ru(bpy)₃²⁺. Intermediates detected by electron paramagnetic resonance spectroscopy include covalent hydrates and hydroxylated bipyridine ligands bound to the metal center. The reaction of Ru(bpy)₃³⁺-zeolite Y with water is considerably accelerated (hours) in the presence of visible light, even though the intermediate species are similar to the reaction in the dark. The promotion of reactivity in the presence of light is attributed to the nature of visible charge-transfer bands. In the presence of ion-exchanged methyl viologen in neighboring supercages, the disappearance of Ru(bpy)₃³⁺ upon visible light photolysis is further accelerated. We propose that the enhanced reactivity is related to the reaction of the covalent hydrates and hydroxylated species of the ruthenium complex with methyl viologen. The emission and excitation spectra of the products extracted from the zeolite after photolysis of the Ru(bpy)₃³⁺ viologen sample show evidence of formation of pyridones. Previous studies have shown that pyridones are oxidation products of hydroxyl radical adducts of methyl viologen. It is proposed that hydroxyl radicals formed upon photolysis of Ru(bpy)₃³⁺-zeolite Y react with methyl viologen.