Copper(II)-loaded HEU-type zeolite crystals: characterization and evidence of surface complexation with N,N-diethyldithiocarbamate anions

Abstract Copper(II)-loaded HEU-type zeolite crystals (CuHEU) formed by wet-chemical procedures were studied through powder X-ray diffraction (PXRD), scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), electron paramagnetic resonance (EPR), diffuse reflectance UV–Vis spectroscopy [DRS(UV–Vis)], X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques. The copper in the non-stoichiometric and non-homoionic CuHEU crystals was identified as six-coordinated cupric ions, the ligating atoms being both oxygen atoms of the framework basic Lewis sites and water molecules. The resulting Cu(II) complexes adopt a tetragonally distorted octahedral symmetry. Treating the CuHEU material with an aqueous solution of N , N -diethyldithiocarbamato ligands (Et 2 dtc − ) results in the product CuHEU–Et 2 dtc, the structure and properties of which were studied by means of PXRD, SEM–EDS, DRS(UV–Vis), EPR and XPS techniques. The spectroscopic investigation of the material revealed the presence of both CuS and CuO coordination bonds in a novel type of coordination sphere around the Cu 2+ ions forming a complex with the Et 2 dtc ligands supported on the surface of the zeolitic substrate. The surface complexation process does not affect either the oxidation state or the tetragonally distorted octahedral symmetry of the copper(II) grafted onto the zeolitic material. Strong evidence exists indicating that the coordination process involves the nucleophilic substitution of primary coordinated water molecules by the stronger σ-donor Et 2 dtc − ligands.