Control of physicochemical properties and catalytic activity of tris(2,2′-bipyridine)iron(ii) encapsulated within the zeolite Y cavity by alkaline earth metal cations

Abstract

A series of materials containing the tris(2,2′-bipyridine)iron(II) (Fe(bpy)₃²⁺) complex inside zeolite Y cavities with alkaline earth metals (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) as charge compensating cations have been synthesized via a “ship in the bottle” method. The influence of the alkaline earth metal cations on the physicochemical properties and catalytic activity was investigated. The successful formation of the Fe(bpy)₃²⁺ complex was verified by XRD, diffuse-reflectance UV-vis spectroscopy, and Fe K-edge XAFS measurements. The BET surface area and the Fe content decreased in the presence of the larger alkaline earth metal, but the intensity of the MLCT adsorption band of Fe(bpy)₃²⁺ increased with the heavier cation. The electron density of the Fe atoms decreased, and the average interatomic bond distance Fe–N/O and the coordination number increased with the heavier alkaline earth metal cation. The encapsulation of Fe(bpy)₃²⁺ resulted in the creation of a photocatalytic system able to oxidize styrene to benzaldehyde and styrene oxide under visible light irradiation (λ > 430 nm) in the presence of molecular oxygen.