Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

Abstract

Recebido em 5/7/10; aceito em 17/9/10; publicado na web em 25/10/10 Herein, the immobilization of some Schiff base-copper(II) complexes in smectite clays is described as a strategy for the heterogenization of homogeneous catalysts. The obtained materials were characterized by spectroscopic techniques, mostly UV/Vis, EPR, XANES and luminescence spectroscopy. SWy-2 and synthetic Laponite clays were used for the immobilization of two different complexes that have previously shown catalytic activity in the dismutation of superoxide radicals, and disproportionation of hydrogen peroxide. The obtained results indicated the occurrence of an intriguing intramolecular redox process involving copper and the imine ligand at the surface of the clays. These studies are supported by computational calculations.

Polyethyleneimine for copper absorption II: kinetics, selectivity and efficiency from seawater

“…In retrospective comparison with literature, a Schiff-base complex appears to produce a comparable spectrum to that found here. 51,52 This correlates with the FTIR analysis which showed formation of Schiff's bases (imines) in the coating aer cross-linking. It is also consistent with the ToF-SIMS fragmentation suggesting an N-based ligand associated with copper.…”

Electron Paramagnetic Resonance Study of Copper–Ethylenediamine Complex Ion Intercalated in Bentonite

“…The values of α 2 for the enBtx samples are in the range α 2 = 0.77−0.83, indicating that around 80% of the spin population is in the copper d x 2 −y 2 orbital, suggesting a moderate covalency for the σ-bonding. A comparison of these α 2 values with those derived for Cu(pyalen) 2+ immobilized in laponite clay (α 2 = 0.82), 42 Cu(cyclam) 2+ intercalated in hectorite clays (α 2 = 0.79) and saponite (α 2 = 0.80) 41 and Cu(bis-oxazoline) immobilized in laponite (α 2 = 0.79) 40 indicates the similarity of the copper covalency of these strong ligand field copper complexes when introduced in the laminar spaces of two-dimensional inorganic matrices.…”

“…The copper ion was found to be a particularly useful probe, since it has an effective electron spin S = 1/2 and a nuclear spin I = 3/2, which allow the observation of hyperfine lines. Since Cu 2+ EPR spectra are very sensitive to symmetry and strengths of the ligand field in the immediate environment of the paramagnetic ion, the EPR data combined with optical absorption spectroscopy can be used to obtain information about the nature of the ground state of Cu 2+ ions, the covalency of the bonding between the copper 3d orbital and the ligand orbitals, and the presence of tetrahedral distortion around the metal in copper complexes. ,, …”

“…Since Cu 2+ EPR spectra are very sensitive to symmetry and strengths of the ligand field in the immediate environment of the paramagnetic ion, the EPR data combined with optical absorption spectroscopy can be used to obtain information about the nature of the ground state of Cu 2+ ions, the covalency of the bonding between the copper 3d orbital and the ligand orbitals, and the presence of tetrahedral distortion around the metal in copper complexes. 40,42,43 ■ EXPERIMENTAL SECTION Materials and Preparation of the Samples. Bentonite (Sigma) purified and converted in its Na + form used in this work is analyzed by plasma atomic absorption spectroscopy (Perkin-Elmer ICP-OES OPTIMA 1000DV) and presents the global formula Na (0.47) (Al 1.58 Fe 0.17 Mg 0.25 )(Al 0.22 Si 3.78 O 10 ) and a characteristic ion exchange capacity (cec) value, determined experimentally, 44 of 85 mequiv/100 g. CuCl 2 (Merck Co), ZnCl 2 (Merck Co), ethylenediamine (en, Aldrich Co.), and methanol (Merck Co.) were used as received.…”

Estudo de propriedades eletrônicas e estruturais de complexos de cobre

“…A literatura indica que, em geral, estes complexos não são estáveis cineticamente na forma reduzida, sendo reoxidados pelo O 2 [21], entretanto em algumas situações, o composto pode permanecer no estado reduzido, comoé o caso do [Cu(pyalen)] + ( Fig. 1.4) intercalado em estruturas lamelares [114] (anexo III). 13 Realizamos a relaxação estrutural dos ligantes sem o Cu sempre partindo da geometria do complexo.…”