Synthesis, characterization and study of polymeric iron(III) complexes with bidentate p-hydroxy Schiff bases as heterogeneous catalysts

The chelating Schiff base ligands 4-(naphthalen-1-yliminomethyl)-phenol (1) and 4-(naphthalen-2-yliminomethyl)-phenol (11) were obtained by condensation of alpha- or beta-naphthyl amine respectively, with p-hydroxy benzaldehyde. The reaction of the chelating ligands I and II with iron(III)nitrate in aqueous ethanol afforded new coordination polymer complexes poly- [Fe(C10H7-1-N=CH-C6H4-4-O)(3)] (III) and poly-[Fe(C10H7-2-N=CH-C6H4-4-O)(3)] (IV). The Schiff bases and their iron(III) complexes were characterized by various physico-chemical techniques. The chemical formulae of compounds were determined by elemental analyses. It was found that both of these ligands acted as bidentate bridging ligands and thus formed cross-linked hexacoordinated polymeric complexes. The coordination was ascertained from the IR, H-1 NMR and UV-Vis Spectral data of the ligand and complexes wherein, a new weak band at 472 and 466 nm were observed due to symmetry forbidden d-d transitions. The azomethine proton signals in the H-1 NMR spectra of the Schiff bases I and II observed between delta8.45 and 8.55 ppm were observed upfield shifted in the spectra of the complexes. The catalytic properties of the coordination polymers as heterogeneous catalysts were examined by liquid phase hydroxylation of phenol using H2O2 as an oxidant. It was found that these complexes provide high TOF value for the hydroxylation of phenol by H2O2. The % phenol conversion was higher with beta-Schiff base complex IV but the product distribution was almost the same with either of the complex. (C) 2004 Elsevier B.V. All rights reserved.