A conspicuous 27Al-NMR signal at 72 ppm during isomerization of Keggin Al13 ions

[Display omitted] •The study of an unknown signal in 27Al-NMR spectra of aqueous aluminum solutions.•Temperature alone induces isomerization of ε-Keggin-Al13 in the absence of glycine.•The γ-Keggin-Al13 isomer is observed in heat treated solutions without glycine. A sharp signal at 72 ppm was recent...

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Bibliographic Details
Published in:Inorganica Chimica Acta 2021-01, Vol.514, p.120014, Article 120014
Main Authors: Brunson, Kieran G., Colla, Christopher A., Oliveri, Anna F., Pan, Long, Casey, William H.
Format: Article
Language:English
Subjects:
27Al-NMR
Aluminum
Aluminum hydrolysis chemistry
Calcium
Cluster
Glycine
High temperature
Isomerization
Isomers
Keggin
NMR
Nuclear magnetic resonance
Stoichiometry
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Summary:[Display omitted] •The study of an unknown signal in 27Al-NMR spectra of aqueous aluminum solutions.•Temperature alone induces isomerization of ε-Keggin-Al13 in the absence of glycine.•The γ-Keggin-Al13 isomer is observed in heat treated solutions without glycine. A sharp signal at 72 ppm was recently observed in 27Al-NMR spectra during the isomerization of Keggin-Al13 ions in the presence of calcium and glycine [1]. It has been proposed that this signal corresponds to one of the Keggin isomers. Conversion of the most common ε-isomer of the Keggin series of molecules, having the stoichiometry [AlO4Al12(OH)24(OH2)12]7+, is enhanced by the addition of calcium and glycine [2,3]. Here we show that a 72 ppm signal can also be observed in the absence of calcium or glycine; the magnitude of which depends on aluminum concentration and temperature. Additionally, isomerization of the ε-Keggin-Al13 to the γ-Keggin-Al13 isomer was observed in the absence of calcium and glycine at elevated temperatures after several days. Calcium and glycine were previously shown to enhance rates of γ-Keggin-Al13 formation.2.
ISSN:0020-1693
1873-3255
DOI:10.1016/j.ica.2020.120014