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Short Strong Hydrogen Bonds can Hinder Complex Formation: A Stability and Structure Study of Copper(II) Alkyl-N-iminodiacetic Acid Complexes in Aqueous Systems and Solid State

Häggman, Leif and Cassel, Anders and Persson, Ingmar (2021). Short Strong Hydrogen Bonds can Hinder Complex Formation: A Stability and Structure Study of Copper(II) Alkyl-N-iminodiacetic Acid Complexes in Aqueous Systems and Solid State. Journal of Solution Chemistry. 50 , 203-219
[Research article]

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Abstract

In the present study the solution and coordination chemistry of copper(II)-alkyl-N-iminodiacetate systems are studied in aqueous solution by potentiometry, using ion selective copper and pH electrodes, EXAFS (extended X-ray absorption fine structure) and dye probe molecular absorption spectrophotometry. Alkyl-N-iminodiacetates with varying alkyl chain length, methyl (CH3-), n-hexyl (C6H13-), n-dodecyl (C12H25-) and n-octadecyl (C18H37-) were used to tune the amphiphilic properties of the ligands. The polar head groups have both oxygen (hard Lewis base) and nitrogen donor (border-line Lewis base) atoms. This means that metal ions with different bonding characteristics may bind these ligands differently. Furthermore, the chelating properties of the polar head group may be regulated by pH as the acid-base properties of the imine and carboxylic acid groups are different. Copper(II) forms two stable complexes with alkyl-N-iminodiacetates with short alkyl chains, present as monomers in aqueous solution, log(10)beta(1) = 11.10(2), log(10)beta(2) = 19.5(2) for methyl-N-iminodiacetate, and log(10)beta(1) = 12.22(4), log(10)beta(2) = 21.9(2) for n-hexyl-N-iminodiacetate. n-Octadecyl-N-iminodiacetic acid, present as large aggregates in acidic aqueous solution, has short strong hydrogen bonds between carboxylic acid and carboxylate groups in the surface of the aggregates, which hinder complex formation at pH values below 4, obstructs it in the pH region 4-7, while the complex formation behaves as for short-chained alkyl-N-iminodiacetates at pH > 7. The structure around copper in copper(II)-alkyl-N-iminodiacetate complexes in aqueous solution and solid state formed at different pH values and copper(II):alkyl-N-iminodiacetate ratios has been determined by EXAFS. The coordination chemistry of copper(II) shows four strong bonds in the equatorial plane, and two different Cu-O/N bond distances, ca. 0.2 angstrom apart, in the axial positions of a non-centrosymmetric tetragonally elongated octahedron.

Authors/Creators:Häggman, Leif and Cassel, Anders and Persson, Ingmar
Title:Short Strong Hydrogen Bonds can Hinder Complex Formation: A Stability and Structure Study of Copper(II) Alkyl-N-iminodiacetic Acid Complexes in Aqueous Systems and Solid State
Series Name/Journal:Journal of Solution Chemistry
Year of publishing :2021
Volume:50
Page range:203-219
Number of Pages:17
Publisher:SPRINGER/PLENUM PUBLISHERS
ISSN:0095-9782
Language:English
Publication Type:Research article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 104 Chemical Sciences > Physical Chemistry
Keywords:Alkyl-N-iminodiacetate, Copper(II), Complex formation, Structure
URN:NBN:urn:nbn:se:slu:epsilon-p-111020
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-111020
Additional ID:
Type of IDID
DOI10.1007/s10953-020-01050-7
Web of Science (WoS)000614666500001
ID Code:24373
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Department of Molecular Sciences
Deposited By: SLUpub Connector
Deposited On:02 Jun 2021 13:03
Metadata Last Modified:02 Jun 2021 13:11

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