Metal – Aminopolycarboxylic Acid Complexes. II. Studies of Triethylenetetraaminehexaacetic Acid and its Lead(II) Complexes in Aqueous Solution by Proton Magnetic Resonance Spectroscopy

Autor:	J. B. Westmore, P. Letkeman
Rok vydání:	1971
Předmět:	Aqueous solution Organic Chemistry Inorganic chemistry Protonation General Chemistry Catalysis Proton magnetic resonance Metal chemistry.chemical_compound chemistry visual_art visual_art.visual_art_medium Aminopolycarboxylic acid Spectroscopy Equilibrium constant
Zdroj:	Canadian Journal of Chemistry. 49:2086-2095
ISSN:	1480-3291 0008-4042
DOI:	10.1139/v71-339
Popis:	Nuclear magnetic resonance (n.m.r.) spectroscopy was used to determine the preferred protonation sites in TTHA. For its 1:1 complex with Pb(II) the following equilibrium constants for protonation were obtained (triethylenetetraaminehexaacetic acid ≡ H6A)[Formula: see text]The non-protonated complex is considered to have four coplanar (or nearly coplanar) metal–nitrogen bonds with the center carboxylate groups coordinated above and below this plane, and with the terminal carboxylate groups playing only a small part in the coordinate bonding. The first and second protonations of the complex occur preferentially at the terminal and center nitrogen atoms, respectively, on the same side of the complex, accompanied by breaking of the respective metal–nitrogen bonds. This causes partial unwrapping of the complex from one side. Rapid interconversion between configurations in which unwrapping and rewrapping occurs first from one side of the molecule and then from the other leads to simplified n.m.r. spectra.
Databáze:	OpenAIRE
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