Phenoxy-imino ligands: coordination chemistry and binding properties with copper(II) cations

Abstract

Reactions of 2-[{(2-hydroxyethyl)imino}methyl]phenol (L1) and 2-[1-{2-(diethylamino)ethylimino}ethyl]phenol (L3) with copper(II) nitrate yielded monometallic complexes [CuNO3(L1)] (1) and [CuNO3(L3)] (2), respectively. The solid-state structures of 1 and 2 confirmed the κ3-O,N,O’ and κ3-O,N,N’ tridentate binding mode of L1 and L3, respectively. The phenoxy-imino ligands 2-[{(2-hydroxyethyl)imino}methyl]phenol (L1), 2-[{(2-(diethylamino)ethylimino}-methyl]phenol (L2), 2-[1-{2-(diethylamino)ethylimino}ethyl]phenol (L3) and 2-[(2-mercaptoethylimino)methyl]phenol (L4) were also used as model chelating agents for liquid-liquid extraction of copper(II), zinc(II), cadmium(II) and lead(II) cations from water using dichloromethane as the organic solvent. The relative affinities of these chelating ligands for copper(II), zinc(II), cadmium(II) and lead(II) by liquid-liquid extraction were found to be in the order copper(II) > zinc(II) > cadmium(II) > lead(II) in line with the hard-soft acid-base interaction. The ligands L1-L4 showed extraction efficiencies ranging from 75% to 99% for copper(II), 72% to 97% for zinc(II), 64% to 87% for cadmium(II) and 51% to 74% for lead(II). The extraction protocol was successfully applied to sewage effluent.