Y-type zeolite-encapsulated copper(II) salicylidene- p-aminobenzoic Schiff base complex: Synthesis, characterization and carbon monoxide adsorption

Abstract

Copper(II) complex with Schiff base ligand derived from salicyaldehyde and p-aminobenzoic acid was encapsulated in the intracrystalline cavities of NaY zeolite via “ship-in-the-bottle” (in situ assembling of the metal complex from smaller moieties) technique. A comparative FT-IR spectroscopic study of CO adsorption on simple Cu ion exchanged zeolite and the encapsulated complex has been carried out. Detailed characterization of the intrazeolitic complex was performed by X-ray powder diffraction, FT-IR, solid-state UV–Vis, EPR spectral studies and magnetic measurements. Additionally, surface texture and thermal analysis (TG, DTG, DTA) have provided further evidence for successful immobilization of the copper complex inside zeolite Y. The analytical data indicate that Cu(II) ions-exchanged NaY zeolite are coordinated with salicylidene- p-aminobenzoic acid (SPAB) ligand forming dinuclear structure. The structure of the moiety around Cu(II) ions in exchanged Y zeolite is changed upon complexation from tetragonal octahedral to distorted tetrahedral geometry. The EPR spectrum of the encapsulated copper complex exhibited fine structure indicating coordination of nitrogen ligand atom to the metal ion. FT-IR study of CO adsorption revealed that the peaks assigned to Cu I–CO (2156 and 2138 cm −1) species are more stable to thermal evacuation in case of Cu II(SPAB)/Y than analogous in Cu II–Y. The higher reactivity of CO chemisorption can be attributed to the higher density of charges in the complex as compared to that in Cu II–Y. Besides, carbonate, formate and carboxylic species were detected only on Cu II(SPAB)/Y at 50 °C in the region of 1800–1300 cm −1. Geminal Cu I–(CO) 2 (2180 cm −1) species is detected at equilibrium CO pressure on both Cu II–Y and Cu II(SPAB)/Y.