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The Mechanism of Copper(II) Binding by Humic Acid: An Electron Spin Resonance Study of a Copper(II)—Humic Acid Complex and Some Adducts with Nitrogen Donors
Author(s) -
Boyd Stephen A.,
Sommers Lee E.,
Nelson Darrell W.,
West Douglas X.
Publication year - 1981
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1981.03615995004500040014x
Subject(s) - chemistry , electron paramagnetic resonance , adduct , copper , ethylenediamine , nitrogen , oxygen , pyridine , humic acid , inorganic chemistry , crystallography , stereochemistry , medicinal chemistry , organic chemistry , nuclear magnetic resonance , fertilizer , physics
Electron spin resonance (ESR) spectroscopy was used to study the mechanism of Cu 2+ binding by humic acid (HA) extracted from a Chalmers silt loam soil. The Cu‐HA complex and some adducts with nitrogen donors were examined. The ESR data presented showed that the addition of pyridine (py) and 1,10‐phenanthroline (phen) to the Cu‐HA complex resulted in the substitution of coordinated H 2 O ligands by the nitrogen donor ligands without displacement of HA oxygen donor ligands also coordinated to the Cu 2+ center. The addition of a more basic nitrogen donor, ethylenediamine (en), resulted in the displacement from Cu 2+ of both coordinated H 2 O ligands and HA oxygen donors, forming Cu(en) 2 2+ . The g‖ and A‖ values obtained for the py and phen adducts revealed that there were two HA oxygen donors coordinated equatorially to the Cu 2+ center in the original Cu‐HA complex. The characterization of the adducts with phen and en was consistent with the formation of a Cu 2+ chelate in the original Cu‐HA complex, where the two equatorial Cu‐HA oxygen bonds would occupy cis ‐ positions. The crystal field strength of HA oxygen donor ligands coordinated to the Cu 2+ center was stronger than that of H 2 O.