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.

Graphical Abstract

Keywords:

• Phenoxy-imino ligands
• heavy metals
• liquid-liquid extraction
• wastewater

Supplementary material

CCDC numbers 2085316 and 2085317 contain the supplementary crystallographic data for 1 and 2. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgment

The authors thank the University of Embu and the University of KwaZulu-Natal for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research leading to these results received financial support from the University of Embu, VC’s research grant-2019.