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

Copper(II)-loaded HEU-type zeolite crystals (CuHEU) formed by wet-chemical procedures were studied through powder X-ray diffraction (PXRD), scanning e lectron microscopy-energy dispersive spectroscopy (SEM-EDS), electron param agnetic resonance(EPR), diffuse reflectance UV-Vis spectroscopy [DRS(W-Vis) ], X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fin e structure (EXAFS) techniques. The copper in the non-stoichiometric and no n-homoionic CuHEU crystals was identified as six-coordinated cupric ions, t he Ligating atoms being both oxygen atoms of the framework basic Lewis site s 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(W-Vis), EPR and XPS techniques. The spectro scopic 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 Cu2+ ions forming a complex with the Et(2)dtc ligands supported on the surf ace of the zeolitic substrate. The surface complexation process does not af fect either the oxidation state or the tetragonally distorted octahedral sy mmetry of the copper(II) grafted onto the zeolitic material, Strong evidenc e exists indicating that the coordination process involves the nucleophilic substitution of primary coordinated water molecules by the stronger sigma- donor Et(2)dtc(-) ligands. (C) 1999 Elsevier Science B.V. All rights reserv ed.