Preparation, spectroscopic, and electrochemical characterization of metal(II) complexes with Schiff base ligands derived from chitosan: correlations of redox potentials with Hammett parameters

Abstract

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 (-OCH 3 ), 5-fluoro (-F), 5-methyl (-CH 3 ), and 5-nitro (-NO 2 ) derivatives (groups R) and mixing these with FeCl 2 and CuCl 2 in ethanol and with Co(CH 3 COO) 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.

Structural Characterization of BIAN Type Molecules Used in Viscosity Reduction of Alkyl Magnesium Solutions

“…Figure 9 c shows the 1500–1800 cm −1 region of the spectrum of the i-Pr-BIAN and BOMAG in heptane solution under argon, where a double band at 1624 and 1614 cm −1 is visible, but there is none at 1670 cm −1 , as seen in i-Pr-BIAN, or 1664 cm −1 , as in the quenched (alkylated) i-Pr-BIAN (compare to Figure 8 d). Such shifts to lower wavenumbers have already been reported for C = N double bonds interacting with platinum [ 41 ], palladium [ 42 ], ands chromium [ 43 ], as well as iron, cobalt, and copper [ 44 ], are attributed to a decrease in the C = N bond order, due to the coordination of the metal with the imine lone pair, thus proving the interaction of the magnesium in the BOMAG chains with the C = N bind of the BIAN.…”