Geometry of Zn(II) complexes with dissolved organic matter: X-ray studies at variable pH

The structure of Zn(II) complexes with dissolved organic matter (DOM) is an important consideration in developing molecular-level models of Zn(II) speciation, but recent reports favoring the tetrahedral geometry differ from earlier findings that geometry was largely octahedral. In general, the prese...

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Bibliographic Details
Published in:Toxicological and environmental chemistry 2013, Vol.95 (1), p.38-44
Main Authors: Mousavi, Aliyar, Marts, Amy R, Tierney, David L, Cabaniss, Stephen E
Format: Article
Language:English
Subjects:
absorption
Binding
Derivatives
Dissolved organic matter
DOM
EXAFS
Fine structure
freshwater
Ligands
Organic chemicals
Speciation
spectroscopy
Spectrum analysis
Tetrahedra
thiols
X-radiation
X-rays
XANES
Zinc
Zn(II)
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Summary:The structure of Zn(II) complexes with dissolved organic matter (DOM) is an important consideration in developing molecular-level models of Zn(II) speciation, but recent reports favoring the tetrahedral geometry differ from earlier findings that geometry was largely octahedral. In general, the presence of thiolate ligands favors the tetrahedral geometry, while O and N ligands favor the octahedral geometry. This work presents extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopic results, indicating an octahedral geometry over the pH range of 5–9 for a freshwater DOM isolate. Changes in XANES derivatives as a function of pH can be explained in terms of ligand protonation and/or changing ligand groups. Tetrahedral Zn(II)–DOM geometry may be restricted to binding environments containing thiol groups.
ISSN:1029-0486
0277-2248
1029-0486
DOI:10.1080/02772248.2012.734620