Zeolite-encapsulated transition metal chelates: synthesis and characterization

This article reviews some important recent works on the synthesis and characterization of zeolite-encapsulated transition metal complexes containing different organic ligands. Distinct methodologies of preparation, including the in situ one-pot template (IOPT) and flexible ligand methods (FLM) are described. The mode of bonding, composition, overall geometry and surface characteristics have been inferred by various physicochemical characterization techniques. Chemical analysis, spectroscopic methods [Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS) and ultraviolet-visible (UV-Vis)], scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive spectroscopy analysis of X-ray (EDAX), magnetic measurements, N-2-adsorption-desorption and thermogravimetric studies have been proven to be powerful techniques to specify these host-guest nanocomposite materials (HGNM). In some cases, Mossbauer, photoluminescence and cyclic voltammetric data are informative. Recent results dealing with the immobilization of complexes concerning aza, heterocyclic, Schiff base and hydrazone ligands are presented. A comprehensive survey of the investigated materials manifested the successful incorporation of the complexes into the zeolite matrix, without collapsing the crystalline structure of zeolite. Occasionally, some of the encapsulated complexes showed structural properties and chemical behavior which are different from those of the neat complex owing to the zeolite constraints.