Preparation, Spectroscopic, and Electrochemical Characterization of Metal(Ii) Complexes with Schiff Base Ligands Derived from Chitosan: Correlations of Redox Potentials with Hammett Parameters

The chitosan-(Fe(II), Co(II), and Cu(II)) complexes were prepared by mixing chitosan (Chi) powder with a salicylaldehyde (Sal, 5-hydrogen (-H)) and their 5-bromo (-Br), 5-chloro (-Cl), 5-methoxy (-OCH3), 5-fluoro (-F), 5-methyl (-CH3), and 5-nitro (-NO2) derivatives (groups R) and mixing these with FeCl2 and CuCl2 in ethanol and with Co(CH3COO)2 solutions in butanol at 80°C over 8 h in heterogeneous phase, followed by extraction with ethanol and butanol, respectively. The complexes were characterized by FTIR and UV-vis spectroscopy, elemental analysis, and cyclic voltammetry. A linear correlation between the metal formal potential versus the Hammett parameters of the substituents was observed. The electron-withdrawing groups shift the redox potential to positive values, as a result of lowering the energy of the highest occupied molecular orbital. The formal potential was used as a measurement for the driving force of chitosan complexes for redox reactions. © 2014 Taylor & Francis.